What does one mole count?

Exactly 6.02214076 × 10^23 representative particles.

What does a peak in an element's mass spectrum represent?

An isotope with a particular mass-to-charge ratio; for singly charged monatomic ions, the position tracks isotopic mass.

What does an empirical formula show?

The lowest whole-number ratio of the elements' atoms in a compound.

How does a mixture differ from a pure substance at the particle level?

A mixture contains chemically distinct representative units in variable proportions; a pure substance contains one element or compound with fixed composition. Different isotopes do not make an elemental sample a mixture.

Which particles make up an atom's nucleus?

Protons and neutrons. Electrons occupy the space outside the nucleus.

What does a larger binding energy on a PES spectrum mean?

More energy is required to remove that electron, so it is held more strongly by the nucleus.

How does atomic radius generally change across a period and down a group?

It decreases from left to right as effective nuclear charge rises, and it increases down a group as additional electron shells increase distance and shielding.

What typical ion charge do Group 1 metals form?

+1, by losing their one valence electron.

How do you convert moles to particles?

Multiply by Avogadro's number: particles = moles × 6.022 × 10^23 mol^-1.

How is average atomic mass estimated from isotope data?

Add each isotopic mass multiplied by its fractional abundance.

How is an element's mass percent in a compound calculated?

Divide the mass contributed by that element by the compound's molar mass, then multiply by 100%.

How can measured elemental composition reveal a sample's purity?

Compare the measured mass fraction with the fraction expected for the pure compound; a mismatch indicates another component.

How do you build a ground-state electron configuration with the Aufbau principle?

For ordinary ground states, move through the periodic table in atomic-number order, filling each s, p, d, or f block as it appears. The subshell capacities are s², p⁶, d¹⁰, and f¹⁴. For example, Br is [Ar] 4s² 3d¹⁰ 4p⁵.

What does the relative area or height of an ideal PES peak indicate?

The relative number of electrons in the corresponding subshell.

How does first ionization energy generally change across a period and down a group?

It increases from left to right as effective nuclear charge rises, and it decreases down a group as distance and shielding make a valence electron easier to remove.

Why do elements in the same group form similar compounds?

Their ground-state valence patterns repeat, including which outer subshells are full or partly full. That leads to similar bonding and typical ion charges.

How do you convert a sample's mass to moles?

Divide its mass by its molar mass: n = m/M.

Which mass-spectrum interpretation lies outside the usual single-element model used in this deck?

Assigning peaks in mixtures or peaks from multiply charged or polyatomic species; the standard model uses singly charged monatomic ions of one element.

What does the law of definite proportions state?

Every pure sample of a given compound has the same element mass ratios.

Why can two samples of the same mixture have different compositions?

Mixture components are physically combined, so their relative amounts are not fixed by a chemical formula.

How does Coulomb's law connect charge and separation to attraction?

Attraction grows with the magnitude of the charge product and decreases with the square of the separation distance.

Which PES electrons usually appear at the highest binding energy?

Core electrons closest to the nucleus, because they feel the strongest nuclear attraction.

How does electron affinity generally change across a period and down a group?

Electron gain generally becomes more favorable from left to right across a period and less favorable down a group as distance and shielding increase. Stable subshell patterns create substantial exceptions.

Why are alkali metals generally more reactive down the group?

Their valence electron is farther from the nucleus and easier to remove.

How many moles are in 18.0 g of H₂O?

About 0.999 mol. Use 18.0 g ÷ 18.02 g mol^-1.

An element is 75% isotope 10 and 25% isotope 11; what is its average atomic mass?

10.25 u. Calculate (0.75 × 10) + (0.25 × 11).

A compound is 40.0% C, 6.7% H, and 53.3% O by mass; what is its empirical formula?

CH₂O. For a 100 g sample, convert each mass to moles and divide by the smallest amount.

A 10.0 g impure sample contains 8.5 g of the target compound; what is its mass-percent purity?

85%. Calculate (8.5 g ÷ 10.0 g) × 100%.

Which electrons are removed first when a transition metal forms a cation?

Electrons in the occupied orbital with the highest principal quantum number: 4s before 3d. For example, Fe²⁺ is [Ar] 3d⁶.

A PES spectrum has peaks proportional to 2, 2, and 6 electrons; which configuration fits?

1s² 2s² 2p⁶, the configuration of Ne.

How does electronegativity generally change across a period and down a group?

It increases from left to right across a period and decreases down a group as atomic size and shielding increase.

What empirical formula results from Al³⁺ and O²⁻?

Al₂O₃, because two Al³⁺ ions balance three O²⁻ ions.

How does a particle's mass in atomic mass units relate to its molar mass?

The numerical value is the same: a molecular or formula-unit mass of x u corresponds to a molar mass of x g mol^-1.

What does the tallest isotope peak usually indicate in a simple mass spectrum?

The most abundant isotope, assuming comparable detection response and singly charged ions.

How much oxygen is present in 25.0 g of a compound that is 32.0% oxygen by mass?

8.00 g O. Multiply 25.0 g by 0.320.

What does a particle diagram with two unbonded species in changing ratios represent?

A mixture, because more than one particle type is present and the ratio is not fixed in a formula unit.

What distinguishes valence electrons from core electrons?

Valence electrons are available for bonding or ion formation; main-group valence electrons occupy the outermost shell, while transition metals may also use (n−1)d electrons. Core electrons mainly shield nuclear charge.

Why can PES peak groups reveal an atom's occupied subshells?

Electrons in different subshells require distinct removal energies, producing separate binding-energy groups.

How do ion radii compare with neutral atoms and within an isoelectronic series?

Cations are smaller than their neutral atoms, while anions are larger. Among species with the same electron count, more protons pull the electrons closer and produce the smaller radius.

What formula is expected for a compound between a Group 2 metal M and a Group 17 nonmetal X?

MX₂, because M forms M²⁺ and X forms X⁻.

When is a covalent bond considered nonpolar?

When the bonded atoms have identical or very similar electronegativities, so the shared electron density is distributed approximately evenly.

Why does a bonded pair of atoms have an equilibrium bond length?

At that separation, attractive and repulsive interactions balance at minimum potential energy.

How are particles arranged in an ionic solid?

Cations and anions occupy a repeating three-dimensional lattice held by electrostatic attraction.

What model explains bonding in a metal?

Positive metal cores are held together by attraction to mobile, delocalized valence electrons.

How do you construct a Lewis diagram?

Count total valence electrons, adding electrons for a negative charge and subtracting them for a positive charge. Choose a skeleton, connect atoms with single bonds, complete terminal duets or octets, and place remaining electrons on the central atom. Add multiple bonds if needed, then check the electron total and formal charges.

What does resonance mean in a molecule or ion?

Resonance uses two or more valid Lewis diagrams with the same atom arrangement but different electron placement. The actual electron distribution is a hybrid; equivalent contributors have equal weight.

What determines molecular shape in VSEPR theory?

Electron domains around the central atom arrange to minimize repulsions.

How does an ionic bond differ from a covalent bond?

Ionic bonding is attraction among oppositely charged ions in an extended structure; covalent bonding uses shared electron density between atoms.

What happens to potential energy when bonded atoms are pushed much closer than equilibrium?

Potential energy rises sharply because nucleus–nucleus and electron–electron repulsions dominate.

Why are many ionic solids brittle?

A shifted lattice can align like charges, creating strong repulsion that splits the crystal.

What molecular shapes arise from two electron domains with no lone pairs and from three domains with zero or one lone pair?

Two bonding domains give linear with a 180° angle. Three domains with no lone pairs give trigonal planar with 120° angles; replacing one bond with a lone pair gives bent with an angle slightly below 120°.

AP Chemistry Flashcards: Complete 9-Unit Course Review

Review all nine AP Chemistry units with 450 cards covering concepts, models, equations, calculation setup, and laboratory reasoning.

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Carte: 450 carte
Versione: 2
Pubblicato: 26 agosto 2026
Ultimo aggiornamento: 10 settembre 2026
Licenza: Common knowledge · CC0 1.0
Lingue del pubblico: en
Materia: Chemistry
Livello: AP Chemistry
Tag: advanced-chemistry, advanced-chem-u1, advanced-chem-u2, advanced-chem-u3, advanced-chem-u4, advanced-chem-u5, advanced-chem-u6, advanced-chem-u7, advanced-chem-u8, advanced-chem-u9

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Informazioni su questo mazzo

Review AP® Chemistry through 450 independently written English flashcards arranged in the course's nine-unit sequence. The deck moves from atomic structure and compound structure through properties of substances and mixtures, reactions, kinetics, thermochemistry, equilibrium, acids and bases, and thermodynamics and electrochemistry. Prerequisites come before dependent models and calculations.

What the cards practice

The cards use five recall paths: concept to explanation; model or representation to interpretation; equation to meaning and use; short setup to a result with units and reasoning; and laboratory observation to a chemical conclusion. They cover definitions, relationships, conditions, contrasts, particle and energy models, focused calculation steps, measurements, errors, and visible changes.

Selected reverse and contrast prompts appear only when the reverse direction has one clear standalone target. The deck excludes mechanical permutations, graph-dependent prompts that require a missing figure, copied test formats, long multipart derivations, and visual recall tied to third-party figures. The review scheduler handles long-term spacing after installation.

See the official AP Chemistry course page for College Board's current course requirements.

The Common knowledge · CC0 1.0 label applies only to the independently written prompts, answers, examples, organization, metadata, and inherited original cover, to the extent applicable rights exist. It does not claim ownership of scientific facts or equations.

This is an independent, unofficial study aid. It is not affiliated with, endorsed by, sponsored by, or official material from College Board or the AP Program. AP® is a trademark registered by the College Board, which is not affiliated with, and does not endorse, this product. No College Board examination questions, answer choices, scoring materials, curriculum text, logos, or trade dress were copied.

Carte in questo mazzo

Carta 1
Domanda
What does one mole count?
Risposta
Exactly 6.02214076 × 10^23 representative particles.
Carta 2
Domanda
What does a peak in an element's mass spectrum represent?
Risposta
An isotope with a particular mass-to-charge ratio; for singly charged monatomic ions, the position tracks isotopic mass.
Carta 3
Domanda
What does an empirical formula show?
Risposta
The lowest whole-number ratio of the elements' atoms in a compound.
Carta 4
Domanda
How does a mixture differ from a pure substance at the particle level?
Risposta
A mixture contains chemically distinct representative units in variable proportions; a pure substance contains one element or compound with fixed composition. Different isotopes do not make an elemental sample a mixture.
Carta 5
Domanda
Which particles make up an atom's nucleus?
Risposta
Protons and neutrons. Electrons occupy the space outside the nucleus.
Carta 6
Domanda
What does a larger binding energy on a PES spectrum mean?
Risposta
More energy is required to remove that electron, so it is held more strongly by the nucleus.
Carta 7
Domanda
How does atomic radius generally change across a period and down a group?
Risposta
It decreases from left to right as effective nuclear charge rises, and it increases down a group as additional electron shells increase distance and shielding.
Carta 8
Domanda
What typical ion charge do Group 1 metals form?
Risposta
+1, by losing their one valence electron.
Carta 9
Domanda
How do you convert moles to particles?
Risposta
Multiply by Avogadro's number: particles = moles × 6.022 × 10^23 mol^-1.
Carta 10
Domanda
How is average atomic mass estimated from isotope data?
Risposta
Add each isotopic mass multiplied by its fractional abundance.
Carta 11
Domanda
How is an element's mass percent in a compound calculated?
Risposta
Divide the mass contributed by that element by the compound's molar mass, then multiply by 100%.
Carta 12
Domanda
How can measured elemental composition reveal a sample's purity?
Risposta
Compare the measured mass fraction with the fraction expected for the pure compound; a mismatch indicates another component.
Carta 13
Domanda
How do you build a ground-state electron configuration with the Aufbau principle?
Risposta
For ordinary ground states, move through the periodic table in atomic-number order, filling each s, p, d, or f block as it appears. The subshell capacities are s², p⁶, d¹⁰, and f¹⁴. For example, Br is [Ar] 4s² 3d¹⁰ 4p⁵.
Carta 14
Domanda
What does the relative area or height of an ideal PES peak indicate?
Risposta
The relative number of electrons in the corresponding subshell.
Carta 15
Domanda
How does first ionization energy generally change across a period and down a group?
Risposta
It increases from left to right as effective nuclear charge rises, and it decreases down a group as distance and shielding make a valence electron easier to remove.
Carta 16
Domanda
Why do elements in the same group form similar compounds?
Risposta
Their ground-state valence patterns repeat, including which outer subshells are full or partly full. That leads to similar bonding and typical ion charges.
Carta 17
Domanda
How do you convert a sample's mass to moles?
Risposta
Divide its mass by its molar mass: n = m/M.
Carta 18
Domanda
Which mass-spectrum interpretation lies outside the usual single-element model used in this deck?
Risposta
Assigning peaks in mixtures or peaks from multiply charged or polyatomic species; the standard model uses singly charged monatomic ions of one element.
Carta 19
Domanda
What does the law of definite proportions state?
Risposta
Every pure sample of a given compound has the same element mass ratios.
Carta 20
Domanda
Why can two samples of the same mixture have different compositions?
Risposta
Mixture components are physically combined, so their relative amounts are not fixed by a chemical formula.
Carta 21
Domanda
How does Coulomb's law connect charge and separation to attraction?
Risposta
Attraction grows with the magnitude of the charge product and decreases with the square of the separation distance.
Carta 22
Domanda
Which PES electrons usually appear at the highest binding energy?
Risposta
Core electrons closest to the nucleus, because they feel the strongest nuclear attraction.
Carta 23
Domanda
How does electron affinity generally change across a period and down a group?
Risposta
Electron gain generally becomes more favorable from left to right across a period and less favorable down a group as distance and shielding increase. Stable subshell patterns create substantial exceptions.
Carta 24
Domanda
Why are alkali metals generally more reactive down the group?
Risposta
Their valence electron is farther from the nucleus and easier to remove.
Carta 25
Domanda
How many moles are in 18.0 g of H₂O?
Risposta
About 0.999 mol. Use 18.0 g ÷ 18.02 g mol^-1.
Carta 26
Domanda
An element is 75% isotope 10 and 25% isotope 11; what is its average atomic mass?
Risposta
10.25 u. Calculate (0.75 × 10) + (0.25 × 11).
Carta 27
Domanda
A compound is 40.0% C, 6.7% H, and 53.3% O by mass; what is its empirical formula?
Risposta
CH₂O. For a 100 g sample, convert each mass to moles and divide by the smallest amount.
Carta 28
Domanda
A 10.0 g impure sample contains 8.5 g of the target compound; what is its mass-percent purity?
Risposta
85%. Calculate (8.5 g ÷ 10.0 g) × 100%.
Carta 29
Domanda
Which electrons are removed first when a transition metal forms a cation?
Risposta
Electrons in the occupied orbital with the highest principal quantum number: 4s before 3d. For example, Fe²⁺ is [Ar] 3d⁶.
Carta 30
Domanda
A PES spectrum has peaks proportional to 2, 2, and 6 electrons; which configuration fits?
Risposta
1s² 2s² 2p⁶, the configuration of Ne.
Carta 31
Domanda
How does electronegativity generally change across a period and down a group?
Risposta
It increases from left to right across a period and decreases down a group as atomic size and shielding increase.
Carta 32
Domanda
What empirical formula results from Al³⁺ and O²⁻?
Risposta
Al₂O₃, because two Al³⁺ ions balance three O²⁻ ions.
Carta 33
Domanda
How does a particle's mass in atomic mass units relate to its molar mass?
Risposta
The numerical value is the same: a molecular or formula-unit mass of x u corresponds to a molar mass of x g mol^-1.
Carta 34
Domanda
What does the tallest isotope peak usually indicate in a simple mass spectrum?
Risposta
The most abundant isotope, assuming comparable detection response and singly charged ions.
Carta 35
Domanda
How much oxygen is present in 25.0 g of a compound that is 32.0% oxygen by mass?
Risposta
8.00 g O. Multiply 25.0 g by 0.320.
Carta 36
Domanda
What does a particle diagram with two unbonded species in changing ratios represent?
Risposta
A mixture, because more than one particle type is present and the ratio is not fixed in a formula unit.
Carta 37
Domanda
What distinguishes valence electrons from core electrons?
Risposta
Valence electrons are available for bonding or ion formation; main-group valence electrons occupy the outermost shell, while transition metals may also use (n−1)d electrons. Core electrons mainly shield nuclear charge.
Carta 38
Domanda
Why can PES peak groups reveal an atom's occupied subshells?
Risposta
Electrons in different subshells require distinct removal energies, producing separate binding-energy groups.
Carta 39
Domanda
How do ion radii compare with neutral atoms and within an isoelectronic series?
Risposta
Cations are smaller than their neutral atoms, while anions are larger. Among species with the same electron count, more protons pull the electrons closer and produce the smaller radius.
Carta 40
Domanda
What formula is expected for a compound between a Group 2 metal M and a Group 17 nonmetal X?
Risposta
MX₂, because M forms M²⁺ and X forms X⁻.
Carta 41
Domanda
When is a covalent bond considered nonpolar?
Risposta
When the bonded atoms have identical or very similar electronegativities, so the shared electron density is distributed approximately evenly.
Carta 42
Domanda
Why does a bonded pair of atoms have an equilibrium bond length?
Risposta
At that separation, attractive and repulsive interactions balance at minimum potential energy.
Carta 43
Domanda
How are particles arranged in an ionic solid?
Risposta
Cations and anions occupy a repeating three-dimensional lattice held by electrostatic attraction.
Carta 44
Domanda
What model explains bonding in a metal?
Risposta
Positive metal cores are held together by attraction to mobile, delocalized valence electrons.
Carta 45
Domanda
How do you construct a Lewis diagram?
Risposta
Count total valence electrons, adding electrons for a negative charge and subtracting them for a positive charge. Choose a skeleton, connect atoms with single bonds, complete terminal duets or octets, and place remaining electrons on the central atom. Add multiple bonds if needed, then check the electron total and formal charges.
Carta 46
Domanda
What does resonance mean in a molecule or ion?
Risposta
Resonance uses two or more valid Lewis diagrams with the same atom arrangement but different electron placement. The actual electron distribution is a hybrid; equivalent contributors have equal weight.
Carta 47
Domanda
What determines molecular shape in VSEPR theory?
Risposta
Electron domains around the central atom arrange to minimize repulsions.
Carta 48
Domanda
How does an ionic bond differ from a covalent bond?
Risposta
Ionic bonding is attraction among oppositely charged ions in an extended structure; covalent bonding uses shared electron density between atoms.
Carta 49
Domanda
What happens to potential energy when bonded atoms are pushed much closer than equilibrium?
Risposta
Potential energy rises sharply because nucleus–nucleus and electron–electron repulsions dominate.
Carta 50
Domanda
Why are many ionic solids brittle?
Risposta
A shifted lattice can align like charges, creating strong repulsion that splits the crystal.
Carta 51
Domanda
What molecular shapes arise from two electron domains with no lone pairs and from three domains with zero or one lone pair?
Risposta
Two bonding domains give linear with a 180° angle. Three domains with no lone pairs give trigonal planar with 120° angles; replacing one bond with a lone pair gives bent with an angle slightly below 120°.
Carta 52
Domanda
Why are metals electrically conductive as solids?
Risposta
Their delocalized electrons can move through the solid when an electric field is applied.
Carta 53
Domanda
How is formal charge calculated for an atom in a Lewis diagram?
Risposta
Formal charge = valence electrons − nonbonding electrons − half the bonding electrons.
Carta 54
Domanda
Why can't electronegativity difference alone classify a bond as ionic or covalent?
Risposta
Bonding lies on a continuum. A larger difference means more ionic character, but the element types and especially the compound's properties give the best classification.
Carta 55
Domanda
Which shapes and bond-angle trends arise as lone pairs replace bonds in four electron domains?
Risposta
Four bonds give tetrahedral with ideal 109.5° angles. One lone pair gives trigonal pyramidal with smaller angles; two lone pairs give bent with typically smaller angles again because lone pairs repel more strongly than bonding pairs.
Carta 56
Domanda
What feature of a potential-energy curve represents bond dissociation energy?
Risposta
The energy difference from the curve's minimum to the separated-atoms limit.
Carta 57
Domanda
When does an ionic compound conduct electricity?
Risposta
When molten or dissolved so its ions can move; not as a rigid solid lattice.
Carta 58
Domanda
What is a substitutional alloy?
Risposta
An alloy in which atoms of a similar size replace some host-metal atoms in the lattice.
Carta 59
Domanda
How do two, three, and four electron domains map to hybridization?
Risposta
Two domains map to sp, three to sp², and four to sp³, with ideal angles of 180°, 120°, and 109.5°. Hybridization involving d orbitals is outside this deck’s scope.
Carta 60
Domanda
What usually makes one resonance contributor more favorable than another?
Risposta
Smaller formal-charge magnitudes, appropriate negative charge on more electronegative atoms, and complete valence shells where applicable.
Carta 61
Domanda
How many sigma and pi bonds are in single, double, and triple bonds?
Risposta
A single bond has one sigma bond; a double has one sigma and one pi bond; a triple has one sigma and two pi bonds. Head-on sigma overlap is stronger than side-by-side pi overlap.
Carta 62
Domanda
Why is a polar covalent bond polar?
Risposta
Unequal electronegativity creates an uneven sharing of electron density and partial charges.
Carta 63
Domanda
Which molecular shapes arise as lone pairs replace bonds in five electron domains?
Risposta
Five bonds give trigonal bipyramidal; four bonds and one lone pair give seesaw; three bonds and two lone pairs give T-shaped; two bonds and three lone pairs give linear.
Carta 64
Domanda
How do ionic charge and ionic radius affect attraction between ions?
Risposta
Larger charge magnitudes and smaller ionic radii produce stronger attraction because the charge product increases and the ion centers are closer.
Carta 65
Domanda
Why do ionic solids often have high melting points?
Risposta
Many strong Coulombic attractions throughout the lattice must be overcome to free the ions.
Carta 66
Domanda
What is an interstitial alloy?
Risposta
A smaller atom occupies holes between host-metal atoms, often making lattice layers harder to slide.
Carta 67
Domanda
What shape has six bonding domains and no lone pairs on the central atom?
Risposta
Octahedral.
Carta 68
Domanda
Which elements commonly form incomplete octets in stable Lewis diagrams?
Risposta
Hydrogen forms a duet, and electron-deficient central atoms such as boron or beryllium can have fewer than eight electrons.
Carta 69
Domanda
How do bond order and atomic size affect covalent bond length and strength?
Risposta
Within a comparable bond family, higher bond order gives shorter, stronger bonds. Larger bonded atoms generally give longer bonds, which are often weaker because their orbitals overlap less effectively.
Carta 70
Domanda
What bonding model best fits a sample that is malleable and conducts as a solid?
Risposta
Metallic bonding with mobile, delocalized electrons and nondirectional attractions.
Carta 71
Domanda
What shape has six electron domains, five bonds, and one lone pair?
Risposta
Square pyramidal.
Carta 72
Domanda
Which lattice should have stronger attractions: MgO or NaCl, assuming similar separations?
Risposta
MgO, because the charge product for Mg²⁺ and O²⁻ is larger than for Na⁺ and Cl⁻.
Carta 73
Domanda
Why are pure metals often malleable?
Risposta
Metal cores can shift while the mobile electron sea maintains nondirectional attraction instead of exposing fixed like-charge planes.
Carta 74
Domanda
What is the best Lewis structure for CO₂?
Risposta
O=C=O, with two lone pairs on each oxygen and no formal charges.
Carta 75
Domanda
What shape has six electron domains, four bonds, and two opposite lone pairs?
Risposta
Square planar.
Carta 76
Domanda
What limitation does an odd total number of valence electrons create for a Lewis diagram?
Risposta
At least one electron must remain unpaired, so not every atom can have a complete paired-electron octet.
Carta 77
Domanda
What does a higher bond order do to a bond's potential-energy curve?
Risposta
It generally places the minimum at a shorter internuclear distance and makes the well deeper, corresponding to a shorter bond and a larger bond-dissociation energy.
Carta 78
Domanda
When can a carbon–carbon double bond produce geometric isomers?
Risposta
When each carbon has two different substituents. The pi bond restricts rotation, so distinct spatial arrangements can persist.
Carta 79
Domanda
When may a third-period central atom exceed an octet in a Lewis diagram?
Risposta
When the valid electron count and lower formal charges favor an expanded valence shell, as in species such as SF₆.
Carta 80
Domanda
How do you decide whether a molecule with polar bonds is polar overall?
Risposta
Add the bond-dipole vectors using the molecular shape; symmetry may cancel them, while an asymmetric arrangement leaves a net dipole.
Carta 81
Domanda
Which interparticle forces act between all atoms and molecules?
Risposta
London dispersion forces, caused by temporary and induced dipoles.
Carta 82
Domanda
What four broad solid types does this deck compare?
Risposta
Ionic, metallic, molecular, and covalent-network solids.
Carta 83
Domanda
How do gas particles differ from liquid particles?
Risposta
Gas particles are much farther apart and move independently; liquid particles stay close but can move past one another.
Carta 84
Domanda
What relationship connects pressure, volume, amount, and temperature for an ideal gas?
Risposta
PV = nRT, with absolute temperature in kelvins and units consistent with R.
Carta 85
Domanda
What does temperature measure in kinetic molecular theory?
Risposta
The particles' average translational kinetic energy.
Carta 86
Domanda
What two ideal-gas assumptions fail most clearly for real gases?
Risposta
Particles have nonzero volume and experience intermolecular attractions.
Carta 87
Domanda
How is molarity defined?
Risposta
Moles of solute per liter of solution: M = n/V.
Carta 88
Domanda
What must a correct particulate diagram of NaCl(aq) show?
Risposta
Separated Na⁺ and Cl⁻ ions in a 1:1 ratio, each surrounded by oriented water molecules.
Carta 89
Domanda
Which separation method removes an insoluble solid from a liquid?
Risposta
Filtration: the solid stays as residue while the liquid passes as filtrate.
Carta 90
Domanda
What does “like dissolves like” mean at the particle level?
Risposta
A solute tends to dissolve when new solute–solvent attractions can compete with the attractions disrupted in the pure substances.
Carta 91
Domanda
What happens when matter absorbs electromagnetic radiation?
Risposta
Its particles move to an allowed higher-energy state when the photon energy matches the energy gap.
Carta 92
Domanda
Which equations connect photon energy, frequency, and wavelength?
Risposta
E = hν and c = λν.
Carta 93
Domanda
What is the Beer–Lambert law?
Risposta
A = εbc: absorbance equals molar absorptivity at the chosen wavelength times path length times concentration.
Carta 94
Domanda
What molecular features generally strengthen London dispersion forces?
Risposta
More electrons and a more polarizable cloud strengthen temporary dipoles; greater contact area and accessible π-electron density can also strengthen the attraction.
Carta 95
Domanda
Why do molecular solids usually have low melting points and fail to conduct electricity?
Risposta
Distinct molecules are held together by relatively weak intermolecular forces, while their valence electrons stay localized in bonds and lone pairs.
Carta 96
Domanda
How do particles move in a solid?
Risposta
They vibrate about fixed positions and do not translate past one another.
Carta 97
Domanda
What graph shapes connect V or P with T(K) or n for an ideal gas?
Risposta
All four are straight lines through the origin: V versus T(K) at fixed n and P; P versus T(K) at fixed n and V; V versus n at fixed P and T; and P versus n at fixed V and T.
Carta 98
Domanda
At the same temperature, which gas has the greater average molecular speed: He or Xe?
Risposta
He. Both have the same average kinetic energy, but KE = ½mv² means the lower-mass particles move faster.
Carta 99
Domanda
Why do real gases deviate more at high pressure?
Risposta
Particles are crowded, so their own volume is no longer negligible compared with the container volume.
Carta 100
Domanda
Which relationship describes dilution when solute amount is conserved?
Risposta
M₁V₁ = M₂V₂.
Carta 101
Domanda
Why does an aqueous ionic solution conduct electricity?
Risposta
Dissolved ions are mobile and carry charge through the solution.
Carta 102
Domanda
Which property lets simple distillation separate two liquids?
Risposta
A sufficient difference in volatility or boiling point, so the vapor is enriched in the more volatile component.
Carta 103
Domanda
Why are many ionic compounds soluble in water but poorly soluble in a nonpolar solvent?
Risposta
Water can form strong ion–dipole attractions that stabilize separated ions; a nonpolar solvent cannot provide comparable attractions.
Carta 104
Domanda
Which molecular transition is commonly associated with microwave absorption?
Risposta
A transition between quantized rotational energy levels.
Carta 105
Domanda
What frequency corresponds to a 600. nm photon?
Risposta
5.00 × 10^14 s^-1. Use ν = c/λ with 600. nm = 6.00 × 10^-7 m.
Carta 106
Domanda
What is the absorbance to two significant figures when ε = 2.0 × 10² L mol^-1 cm^-1, b = 1.00 cm, and c = 0.0020 M?
Risposta
0.40. Use A = εbc.
Carta 107
Domanda
What conditions allow hydrogen bonding between two molecules?
Risposta
One molecule must donate an H covalently bonded to N, O, or F, and the other must provide a lone pair on N, O, or F. A molecule can be a donor, an acceptor, or both.
Carta 108
Domanda
Why are covalent-network solids often very hard with high melting points?
Risposta
A continuous network of strong covalent bonds must be disrupted to deform or melt the solid.
Carta 109
Domanda
Why do a substance's solid and liquid phases usually have similar molar volumes?
Risposta
Their particles remain in close contact in both phases, even though liquid particles can move past one another.
Carta 110
Domanda
How is a gas mixture's total pressure related to its component pressures?
Risposta
Ptotal = ΣPi; each partial pressure is the pressure that component would exert alone in the same volume and temperature.
Carta 111
Domanda
What microscopic events create gas pressure?
Risposta
Gas particles collide with container walls and transfer momentum.
Carta 112
Domanda
Why do intermolecular attractions matter more for gases at low temperature?
Risposta
Particles move more slowly, so attractions can alter their paths and promote condensation.
Carta 113
Domanda
What is the final concentration after 50.0 mL of 2.00 M solution is diluted to 200.0 mL?
Risposta
0.500 M. Use M₂ = M₁V₁/V₂.
Carta 114
Domanda
What must a particulate representation of a solution communicate?
Risposta
The relative concentrations of its components and the particle-level interactions among those components.
Carta 115
Domanda
What causes components to separate in chromatography?
Risposta
They differ in attraction to the stationary phase and the mobile phase, so they travel at different rates.
Carta 116
Domanda
Why are many polar molecular solutes soluble in water?
Risposta
Dipole attractions or hydrogen bonds with water can replace the solute–solute and water–water attractions disrupted during mixing.
Carta 117
Domanda
Why does an atom produce discrete spectral lines?
Risposta
Its electrons can occupy only quantized energy levels, so only photons matching allowed energy differences are absorbed or emitted.
Carta 118
Domanda
How does photon energy change when frequency doubles?
Risposta
It doubles because E = hν.
Carta 119
Domanda
Why is a calibration curve useful in spectrophotometry?
Risposta
It relates measured absorbance to known concentrations, letting an unknown concentration be read by interpolation within the linear range.
Carta 120
Domanda
How does an ion–dipole attraction form, and how does it compare with dipole–dipole attraction?
Risposta
An ion attracts the oppositely charged end of a polar molecule. Ion–dipole attractions tend to be stronger than dipole–dipole attractions.
Carta 121
Domanda
Which solid type is usually both conductive and malleable?
Risposta
A metallic solid, because its delocalized electrons move and its nondirectional bonding tolerates layer shifts.
Carta 122
Domanda
How does a crystalline solid differ from an amorphous solid?
Risposta
A crystalline solid has long-range repeating order; an amorphous solid lacks that long-range periodic arrangement.
Carta 123
Domanda
How is a gas component's partial pressure found from mole fraction?
Risposta
Pi = XiPtotal.
Carta 124
Domanda
How does heating a fixed-volume gas affect its pressure in the ideal model?
Risposta
Pressure rises because faster particles collide with the walls more forcefully and frequently.
Carta 125
Domanda
Why can attractions make a real gas's measured pressure lower than the ideal prediction?
Risposta
Attractions pull approaching particles away from the walls, reducing momentum transfer during wall collisions.
Carta 126
Domanda
How many moles of ions result from complete dissolution of 0.20 mol CaCl₂?
Risposta
0.60 mol ions: 0.20 mol Ca²⁺ plus 0.40 mol Cl⁻.
Carta 127
Domanda
How should water orient around Cl⁻ in a particle model?
Risposta
Its partially positive hydrogen ends point toward Cl⁻.
Carta 128
Domanda
Can filtration separate dissolved components of a liquid solution?
Risposta
No. Dissolved particles pass through the filter with the solvent; filtration only retains an insoluble solid.
Carta 129
Domanda
Why do nonpolar molecular solutes often dissolve in nonpolar solvents?
Risposta
Both rely mainly on compatible London dispersion forces, so mixing can replace the attractions disrupted in the separate substances.
Carta 130
Domanda
What does a shorter absorbed wavelength imply about an energy transition?
Risposta
A larger energy gap because E = hc/λ.
Carta 131
Domanda
What is the energy of a photon with frequency 5.0 × 10^14 s^-1?
Risposta
3.3 × 10^-19 J. Multiply by Planck's constant: E = (6.626 × 10^-34 J·s)(5.0 × 10^14 s^-1).
Carta 132
Domanda
How does doubling cuvette path length affect absorbance in the linear Beer–Lambert range?
Risposta
Absorbance doubles if concentration and molar absorptivity stay constant.
Carta 133
Domanda
How can noncovalent interactions affect a large biomolecule?
Risposta
Attractions between molecules or between different regions of the same molecule help set its shape, which strongly affects its properties and function.
Carta 134
Domanda
Why does an ionic solid usually fail to conduct as a solid?
Risposta
Its ions are fixed in lattice positions. The same substance conducts when molten or dissolved because the ions can then move.
Carta 135
Domanda
Why does a gas have no definite shape or volume?
Risposta
Its widely spaced particles move constantly and experience minimal interparticle attraction, so they spread through the available container.
Carta 136
Domanda
What graph shapes show the inverse pressure–volume relationship for a fixed amount of ideal gas at constant temperature?
Risposta
A plot of P against V is a decreasing curve, while P against 1/V is a straight line through the origin.
Carta 137
Domanda
At the same temperature, do different ideal gases have different average kinetic energies?
Risposta
No. Average translational kinetic energy depends only on absolute temperature.
Carta 138
Domanda
Under which conditions is ideal-gas behavior most accurate?
Risposta
Low pressure and high temperature, where particles are far apart and attractions matter least.
Carta 139
Domanda
What particle-level feature distinguishes a solution from a heterogeneous mixture?
Risposta
A solution—whether solid, liquid, or gas—is uniform throughout; a heterogeneous mixture has regions or phases with different compositions.
Carta 140
Domanda
How should water orient around Na⁺ in a particulate model?
Risposta
Its partially negative oxygen end points toward Na⁺.
Carta 141
Domanda
In paper chromatography, why does one solute spot travel farther than another?
Risposta
It interacts more strongly with the mobile phase or more weakly with the stationary phase. With known phase polarities, that travel difference can reveal relative solute polarity.
Carta 142
Domanda
What energy competition helps explain whether an ionic solid dissolves?
Risposta
The energy needed to separate lattice ions competes with the energy released when ion–solvent attractions form.
Carta 143
Domanda
Which molecular motions commonly absorb infrared radiation?
Risposta
Bond vibrations whose changing dipole can interact with the radiation.
Carta 144
Domanda
Why must wavelength be converted to meters in c = λν when c is in m s^-1?
Risposta
Consistent units are required so meters cancel correctly and frequency comes out in s^-1.
Carta 145
Domanda
How can fingerprints on a cuvette affect a visible-light absorbance reading?
Risposta
They can absorb or scatter extra light, making measured absorbance too high and the inferred concentration too high.
Carta 146
Domanda
What causes and controls the strength of dipole–dipole attractions?
Risposta
Opposite partial charges on neighboring polar molecules attract. Strength increases with larger molecular dipoles and depends on how favorably the dipoles are oriented.
Carta 147
Domanda
Why is graphite conductive and soft while diamond is insulating and hard?
Risposta
Graphite has delocalized electrons within its sheets, so it conducts, and its layers can slide, so it is soft. Diamond has a rigid three-dimensional network of localized covalent bonds, making it hard and insulating.
Carta 148
Domanda
Why are gases much more compressible than liquids?
Risposta
Gas particles have large empty spaces between them; liquid particles are already close together.
Carta 149
Domanda
What volume does 0.500 mol CO₂ occupy at 1.00 atm and 300. K if it behaves ideally?
Risposta
12.3 L. Use V = nRT/P = (0.500 mol)(0.08206 L atm mol^-1 K^-1)(300. K)/(1.00 atm).
Carta 150
Domanda
Why does a lighter gas effuse faster than a heavier gas at the same temperature?
Risposta
Its particles have a higher average speed because equal average kinetic energy is shared by less mass.
Carta 151
Domanda
How does finite particle volume affect a real gas at very high pressure?
Risposta
The free volume available for particle motion is smaller than the container volume assumed by the ideal model.
Carta 152
Domanda
How should 250.0 mL of 0.100 M NaCl be prepared from solid NaCl?
Risposta
Dissolve 0.0250 mol NaCl, or 1.46 g, then dilute to exactly 250.0 mL in a volumetric flask.
Carta 153
Domanda
What changes in a particle diagram when a solution is diluted without losing solute?
Risposta
The solute-particle count stays constant while solvent volume and particle spacing increase.
Carta 154
Domanda
Why is fractional distillation better than simple distillation for liquids with close boiling points?
Risposta
Repeated vaporization–condensation steps enrich the vapor in the more volatile component more effectively.
Carta 155
Domanda
Why are oil and water usually immiscible?
Risposta
Water's strong hydrogen-bond network isn't replaced by equally strong water–oil attractions, so the substances separate into phases.
Carta 156
Domanda
Which molecular transition is commonly associated with ultraviolet or visible absorption?
Risposta
A transition between electronic energy levels.
Carta 157
Domanda
Which photon carries more energy, blue light or red light?
Risposta
Blue light, because it has shorter wavelength and higher frequency.
Carta 158
Domanda
Why is absorbance often measured at the wavelength of maximum absorbance in Beer–Lambert analysis?
Risposta
It gives the largest concentration-sensitive signal, and the flat top near the maximum makes small wavelength-setting errors less influential.
Carta 159
Domanda
What creates a dipole–induced-dipole attraction, and what controls its strength?
Risposta
A permanent dipole distorts a nearby nonpolar particle's electron cloud and creates an attractive temporary dipole. A larger permanent dipole and a more polarizable nonpolar partner make the attraction stronger.
Carta 160
Domanda
How do stronger intermolecular forces affect vapor pressure, boiling point, and melting point?
Risposta
They lower vapor pressure and raise boiling point. Melting point often rises too, but the trend is less direct because melting rearranges rather than fully separates particles.
Carta 161
Domanda
How do particles behave in a liquid?
Risposta
They stay in close contact while moving and colliding continuously. Temperature and interparticle attractions affect their arrangement and motion.
Carta 162
Domanda
Why must Celsius temperature be converted to kelvins in gas-law calculations?
Risposta
Gas-law proportionalities require an absolute temperature scale whose zero corresponds to zero extrapolated thermal motion.
Carta 163
Domanda
How does raising temperature change a Maxwell–Boltzmann speed distribution?
Risposta
The distribution broadens, its peak lowers and shifts right, and a larger fraction of particles have high speed.
Carta 164
Domanda
Why does the ideal-gas model treat collisions as elastic?
Risposta
It assumes total kinetic energy is conserved in particle–particle and particle–wall collisions.
Carta 165
Domanda
How many moles of solute are in 75.0 mL of a 0.400 M solution?
Risposta
0.0300 mol. Multiply 0.400 mol L^-1 by 0.0750 L.
Carta 166
Domanda
For equal solution volumes drawn at the same scale, what shows which solution is more concentrated?
Risposta
The more concentrated diagram contains more solute particles in that equal volume.
Carta 167
Domanda
How do differences in intermolecular attractions let distillation separate a liquid solution?
Risposta
They give the components different vapor pressures, so the vapor is enriched in the more volatile component.
Carta 168
Domanda
What comparison helps predict whether two liquids will be miscible?
Risposta
Liquids with similar types and strengths of intermolecular attractions are more likely to mix uniformly.
Carta 169
Domanda
How can an absorption spectrum help identify a substance?
Risposta
Its allowed energy gaps produce a characteristic pattern of absorbed wavelengths that can be compared with known spectra.
Carta 170
Domanda
How does absorbing or emitting a photon change an atom's or molecule's energy?
Risposta
Absorption raises the species' energy by exactly the photon energy; emission lowers it by the same amount.
Carta 171
Domanda
What macroscopic evidence can support that a chemical reaction occurred?
Risposta
Evidence can include gas formation, precipitate formation, a persistent color change, or an energy change, interpreted with particle-level changes.
Carta 172
Domanda
What does a net ionic equation include?
Risposta
Only the dissolved or reacting species that undergo chemical change; spectator ions are omitted.
Carta 173
Domanda
What must a correct particulate reaction diagram conserve?
Risposta
The number of atoms of every element and the total charge.
Carta 174
Domanda
What distinguishes a chemical change from a physical change?
Risposta
A chemical change rearranges bonds into new substances; a physical change alters state or arrangement without changing chemical identity.
Carta 175
Domanda
What does a balanced equation's coefficient ratio provide?
Risposta
The mole ratio among reacting and produced species.
Carta 176
Domanda
What is the equivalence point of a titration?
Risposta
The point where titrant and analyte have reacted in the stoichiometric ratio given by the balanced equation.
Carta 177
Domanda
What defines a precipitation reaction?
Risposta
Aqueous ions combine to form a sparingly soluble solid.
Carta 178
Domanda
What happens in a Brønsted–Lowry acid–base reaction?
Risposta
A proton transfers from the acid (donor) to the base (acceptor). In aqueous solution, H₂O can play either role.
Carta 179
Domanda
What does oxidation mean in a redox reaction?
Risposta
Loss of electrons and an increase in oxidation number.
Carta 180
Domanda
What particle-level change confirms that a process is chemical?
Risposta
Atoms rearrange into new combinations, producing substances with different compositions.
Carta 181
Domanda
Which ions are spectators when AgNO₃(aq) reacts with NaCl(aq)?
Risposta
Na⁺ and NO₃⁻. The net ionic reaction is Ag⁺(aq) + Cl⁻(aq) → AgCl(s).
Carta 182
Domanda
How does a particulate diagram reveal the limiting reactant?
Risposta
After forming the maximum product allowed by the ratio, none of the limiting reactant remains while excess reactant particles do.
Carta 183
Domanda
Is melting ice a chemical or physical change?
Risposta
A physical change. H₂O molecules remain H₂O while their arrangement and motion change.
Carta 184
Domanda
How is the limiting reactant identified from given amounts?
Risposta
Convert each reactant to the same product amount using the balanced equation; the smaller product amount identifies the limiting reactant.
Carta 185
Domanda
How does an endpoint differ from an equivalence point?
Risposta
The endpoint is an observed signal such as indicator color change; the equivalence point is the exact stoichiometric condition.
Carta 186
Domanda
How is complete combustion of a hydrocarbon in excess oxygen classified, and what products form?
Risposta
It is a redox combustion reaction that forms CO₂ and H₂O.
Carta 187
Domanda
What are the conjugate acid and conjugate base in NH₃ + H₂O ⇌ NH₄⁺ + OH⁻?
Risposta
NH₄⁺ is the conjugate acid of NH₃, and OH⁻ is the conjugate base of H₂O.
Carta 188
Domanda
What does reduction mean in a redox reaction?
Risposta
Gain of electrons and a decrease in oxidation number.
Carta 189
Domanda
Which common changes are physical rather than chemical?
Risposta
Phase changes and the formation or separation of mixtures are physical when each substance keeps its composition.
Carta 190
Domanda
How are strong soluble electrolytes written in a complete ionic equation?
Risposta
As separated aqueous ions; solids, liquids, gases, and weak electrolytes stay intact.
Carta 191
Domanda
A diagram starts with six A particles and four B₂ particles for 2A + B₂ → 2AB; what remains after completion?
Risposta
One B₂ remains. Six A consume three B₂ and form six AB.
Carta 192
Domanda
Why is dissolving NaCl in water normally classified as a physical change?
Risposta
Na⁺ and Cl⁻ separate and become hydrated, but retain their chemical identities. Removing the water recovers NaCl; the shift from ion–ion to ion–dipole attractions does not by itself form a new substance.
Carta 193
Domanda
What mass of AgCl can form from 25.0 mL of 0.200 M AgNO₃ mixed with excess Cl⁻?
Risposta
0.717 g AgCl. The 1:1 reaction gives 0.00500 mol AgCl; multiply by 143.32 g mol^-1.
Carta 194
Domanda
What calculation finds unknown analyte moles at equivalence?
Risposta
Use titrant moles, n = MV, then apply the balanced-reaction mole ratio.
Carta 195
Domanda
Which feature identifies an acid–base, redox, or precipitation reaction?
Risposta
Acid–base reactions transfer protons, redox reactions change oxidation numbers through electron transfer, and precipitation reactions form a sparingly soluble solid.
Carta 196
Domanda
What is the net ionic equation for strong acid–strong base neutralization?
Risposta
H⁺(aq) + OH⁻(aq) → H₂O(l).
Carta 197
Domanda
What is the oxidation number of sulfur in SO₄²⁻?
Risposta
+6. Four oxygens contribute -8 total, so sulfur must be +6 to give -2 overall.
Carta 198
Domanda
Why can gas bubbles alone be ambiguous evidence of reaction?
Risposta
Bubbles may also come from boiling or dissolved gas escaping, so the context and particle identities must support a chemical change.
Carta 199
Domanda
How is melting ice represented as a balanced physical-change equation?
Risposta
H₂O(s) → H₂O(l). The formula and atom count stay the same because only the physical state changes.
Carta 200
Domanda
What does a particle diagram show when no reaction occurs after two aqueous ionic solutions mix?
Risposta
All ions remain separated and solvated, with no new bonded particles, precipitate, or gas.
Carta 201
Domanda
Why is rusting iron a chemical change?
Risposta
Iron atoms form new iron-oxide substances through electron transfer and new bonding.
Carta 202
Domanda
For 2H₂O₂(aq) → 2H₂O(l) + O₂(g), what volume of O₂ forms from 0.100 mol H₂O₂ at 298 K and 1.00 atm?
Risposta
1.22 L O₂. The mole ratio gives 0.0500 mol O₂, then V = nRT/P.
Carta 203
Domanda
A 25.0 mL monoprotic acid sample requires 20.0 mL of 0.150 M NaOH; what is the acid concentration?
Risposta
0.120 M. At 1:1 equivalence, moles acid = 0.0200 L × 0.150 M, then divide by 0.0250 L.
Carta 204
Domanda
Which salts does the minimum solubility rule in this deck treat as soluble?
Risposta
All salts containing Na⁺, K⁺, NH₄⁺, or NO₃⁻ are treated as soluble in water.
Carta 205
Domanda
How are the strengths of a conjugate acid and its conjugate base related?
Risposta
A stronger acid has a weaker conjugate base, and a stronger base has a weaker conjugate acid.
Carta 206
Domanda
How are oxidation and reduction half-reactions combined into one balanced equation?
Risposta
Multiply them so electrons lost equal electrons gained, add the half-reactions, then cancel electrons and any identical species on both sides.
Carta 207
Domanda
How do molecular, complete ionic, and net ionic equations differ?
Risposta
Molecular equations keep compounds intact, complete ionic equations split strong soluble electrolytes, and net ionic equations remove spectators. All three conserve atoms and charge.
Carta 208
Domanda
How should coefficients change particle counts in a reaction diagram?
Risposta
They set whole-particle ratios while preserving each particle's chemical formula.
Carta 209
Domanda
Is separating a mixture by distillation a chemical or physical change?
Risposta
A physical change. Components change phase and location but keep their chemical identities.
Carta 210
Domanda
What equation results from Cu → Cu²⁺ + 2e⁻ and Ag⁺ + e⁻ → Ag?
Risposta
Cu + 2Ag⁺ → Cu²⁺ + 2Ag. Multiply the silver half-reaction by 2 and cancel 2e⁻; both atom counts and net charge then match.
Carta 211
Domanda
How is average reaction rate found from a reactant concentration?
Risposta
Use the negative concentration change divided by elapsed time, adjusted by its stoichiometric coefficient when comparing species rates.
Carta 212
Domanda
What does a rate law express?
Risposta
It shows how the measured rate depends on reactant concentrations. In rate = k[A]^m[B]^n, m and n are the orders in A and B, and m + n is the overall order.
Carta 213
Domanda
A plot of ln[A] versus time is linear; what is the order in A and its integrated rate law?
Risposta
First order: ln[A]t = ln[A]0 − kt, so the plot's slope is −k.
Carta 214
Domanda
What is an elementary reaction?
Risposta
A single step in a mechanism whose rate law follows directly from its reactant molecularity.
Carta 215
Domanda
What two collision conditions are needed for reaction?
Risposta
Sufficient collision energy and a productive molecular orientation.
Carta 216
Domanda
What does activation energy represent on a reaction-energy profile?
Risposta
The energy difference from the reactants to the transition state. The reaction coordinate tracks the step's structural progress, not elapsed time.
Carta 217
Domanda
What must the elementary steps of a valid mechanism do when added?
Risposta
Cancel intermediates and reproduce the overall balanced reaction.
Carta 218
Domanda
How is a proposed mechanism tested against kinetics?
Risposta
Its derived rate law must agree with the experimentally measured rate law.
Carta 219
Domanda
What does a pre-equilibrium approximation assume?
Risposta
A fast reversible step reaches equilibrium before a later slow step consumes its intermediate.
Carta 220
Domanda
What does each peak on a multistep energy profile represent?
Risposta
A transition state for one elementary step.
Carta 221
Domanda
How does a catalyst increase reaction rate?
Risposta
It provides an alternate mechanism with a lower activation-energy pathway.
Carta 222
Domanda
Why does crushing a solid reactant usually increase its reaction rate?
Risposta
Crushing increases exposed surface area, so more reactant particles can collide with the other reactant each second.
Carta 223
Domanda
How is reaction order found from initial-rate data?
Risposta
Compare trials where one reactant concentration changes while the others stay constant, then match the rate factor to the concentration factor.
Carta 224
Domanda
A plot of [A] versus time is linear; what is the order in A and its integrated rate law?
Risposta
Zero order: [A]t = [A]0 − kt, so the plot's slope is −k.
Carta 225
Domanda
What is the rate law for the elementary step 2A + B → products?
Risposta
rate = k[A]²[B]. This inference is valid because the step is elementary.
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Carta 226
Domanda
How does raising temperature change a Maxwell–Boltzmann energy distribution and reaction rate?
Risposta
The distribution shifts and broadens toward higher energies, so a larger fraction of collisions exceeds the activation-energy threshold and can react.
Carta 227
Domanda
How is ΔH read from a reaction-energy profile?
Risposta
ΔH = energy of products − energy of reactants.
Carta 228
Domanda
What is a reaction intermediate?
Risposta
A species formed in one mechanism step and consumed in a later step, so it cancels from the overall equation.
Carta 229
Domanda
Why can't overall reaction coefficients usually supply rate-law exponents?
Risposta
The overall equation hides the mechanism; exponents come from experiment unless the reaction is a stated elementary step.
Carta 230
Domanda
How does pre-equilibrium remove an intermediate from a rate law?
Risposta
Use the fast-step equilibrium relation to express the intermediate concentration in terms of stable reactants.
Carta 231
Domanda
What does each valley between peaks represent on a multistep profile?
Risposta
A reaction intermediate.
Carta 232
Domanda
Does a catalyst change ΔH or the equilibrium constant?
Risposta
No. It changes the pathway and rates, not reactant/product energies or the equilibrium composition.
Carta 233
Domanda
For 2A → B, how are disappearance of A and appearance of B related?
Risposta
Reaction rate = -(1/2)Δ[A]/Δt = Δ[B]/Δt.
Carta 234
Domanda
How do the units of k depend on a rate law's overall order?
Risposta
They must make the rate unit M s^-1: zero order uses M s^-1, first order s^-1, and second order M^-1 s^-1.
Carta 235
Domanda
A plot of 1/[A] versus time is linear; what is the order in A and its integrated rate law?
Risposta
Second order: 1/[A]t = 1/[A]0 + kt, so the plot's slope is +k.
Carta 236
Domanda
What is molecularity?
Risposta
The number of reacting particles in an elementary step, such as unimolecular or bimolecular.
Carta 237
Domanda
How does raising temperature affect k in the qualitative Arrhenius model?
Risposta
k increases, often sharply, because a larger fraction of collisions can reach the transition state. Arrhenius-equation calculations are outside this deck’s scope.
Carta 238
Domanda
A reactant falls from 0.80 M to 0.50 M in 30. s; what is its average disappearance rate to two significant figures?
Risposta
0.010 M s^-1. Use -(0.50 − 0.80) M ÷ 30. s.
Carta 239
Domanda
How does a catalyst differ from an intermediate in a mechanism?
Risposta
A catalyst is consumed early and regenerated later; an intermediate is formed early and consumed later.
Carta 240
Domanda
For 2NO₂ → NO₃ + NO (slow), followed by NO₃ + CO → NO₂ + CO₂ (fast), what rate law is predicted?
Risposta
rate = k[NO₂]². The first step is elementary and rate-limiting, so its molecularity sets the observed rate law.
Carta 241
Domanda
On a multistep reaction-energy profile, which feature often identifies the rate-determining step?
Risposta
The step with the largest activation barrier measured from its preceding valley to its peak.
Carta 242
Domanda
If changing [B] leaves rate unchanged, what is the order in B?
Risposta
Zero order, so [B]^0 = 1 in the measured rate law.
Carta 243
Domanda
What mechanism changes can binding, acid–base, or surface catalysis introduce?
Risposta
They can orient reactants, lower activation barriers, or create new bound, protonated, or deprotonated intermediates and elementary steps; the catalyst is regenerated.
Carta 244
Domanda
What is special about a first-order reaction's half-life?
Risposta
It is constant and independent of starting concentration: t1/2 = ln 2/k. Radioactive decay is a common first-order example.
Carta 245
Domanda
Why is a termolecular elementary collision uncommon?
Risposta
Three particles must collide simultaneously with suitable energy and orientation, which is much less probable than one- or two-particle events.
Carta 246
Domanda
On a reaction-energy profile, how are reverse activation energy, forward activation energy, and ΔH related?
Risposta
Ea,reverse = Ea,forward − ΔH. The reverse barrier is measured from products to the same transition state.
Carta 247
Domanda
Why can correct orientation matter even above the activation energy?
Risposta
The colliding reactive sites must align so old bonds can break and new bonds can form along the reaction pathway.
Carta 248
Domanda
How does detecting a proposed reaction intermediate affect a mechanism claim?
Risposta
It supports a mechanism that contains that intermediate, but it doesn't prove that mechanism is unique.
Carta 249
Domanda
For 2NO ⇌ N₂O₂ (fast equilibrium), followed by N₂O₂ + O₂ → 2NO₂ (slow), what observed rate law results?
Risposta
rate = kobs[NO]²[O₂]. Start with rate = k₂[N₂O₂][O₂], use [N₂O₂] = K[NO]² from the fast equilibrium, then substitute.
Carta 250
Domanda
What does the highest point of a one-step energy profile represent?
Risposta
The transition state, an unstable arrangement at the top of the activation barrier.
Carta 251
Domanda
What sign does q have for an endothermic system?
Risposta
Positive, because the system absorbs heat from the surroundings.
Carta 252
Domanda
How does an exothermic reaction appear on an enthalpy diagram?
Risposta
Products lie below reactants, so ΔH is negative.
Carta 253
Domanda
What condition defines thermal equilibrium?
Risposta
Objects in contact have the same temperature, so there is no net heat transfer.
Carta 254
Domanda
What equations relate heat capacity and temperature change to heat transfer?
Risposta
Use q = mcΔT with specific heat capacity, or q = nCₘΔT with molar heat capacity.
Carta 255
Domanda
Why is temperature constant during a phase-change plateau?
Risposta
Added or removed energy changes interparticle potential energy instead of average kinetic energy.
Carta 256
Domanda
What does ΔHrxn describe?
Risposta
The heat absorbed or released at constant pressure for the reaction exactly as written under the stated conditions.
Carta 257
Domanda
How is reaction enthalpy estimated from average bond enthalpies?
Risposta
ΔHrxn ≈ Σ(bonds broken) − Σ(bonds formed).
Carta 258
Domanda
What is the standard enthalpy of formation of an element in its standard state?
Risposta
Zero by definition.
Carta 259
Domanda
In a Hess’s law calculation, how should a step change when the target needs twice its reverse?
Risposta
Reverse the equation, double every coefficient, and multiply its ΔH by -2.
Carta 260
Domanda
How can energy cross a system boundary during a process?
Risposta
As heat or work. Heat transferred to or work done on the system increases its energy; heat transferred from or work done by the system decreases it.
Carta 261
Domanda
How does an endothermic reaction appear on an enthalpy diagram?
Risposta
Products lie above reactants, so ΔH is positive.
Carta 262
Domanda
How are heat gained by a system and heat lost by its surroundings related in an isolated setup?
Risposta
qsystem = -qsurroundings.
Carta 263
Domanda
In coffee-cup calorimetry, how is reaction heat related to solution heat?
Risposta
qrxn = -qsolution when calorimeter heat is negligible and pressure is constant.
Carta 264
Domanda
What heat is required to melt n moles at the melting point?
Risposta
q = nΔHfus.
Carta 265
Domanda
How does reversing a reaction change ΔH?
Risposta
It reverses the sign of ΔH.
Carta 266
Domanda
Why is breaking a bond endothermic?
Risposta
Energy must be supplied to separate atoms against their bonding attraction.
Carta 267
Domanda
How is ΔH°rxn calculated from standard enthalpies of formation?
Risposta
ΣνΔHf°(products) − ΣνΔHf°(reactants).
Carta 268
Domanda
How does multiplying an equation by 3 affect its ΔH?
Risposta
Multiply ΔH by 3 because enthalpy change scales with reaction amount.
Carta 269
Domanda
Why can an exothermic dissolution warm the solution?
Risposta
The solution warms because forming solute–solvent attractions releases more energy than is absorbed in separating the original particles. The net potential-energy decrease raises particle kinetic energy and temperature.
Carta 270
Domanda
Does an energy diagram's activation barrier determine ΔH?
Risposta
No. ΔH depends on reactant and product energy levels, while the barrier controls kinetics.
Carta 271
Domanda
Why does heat flow from a warmer object to a cooler object?
Risposta
Energy transfers through collisions until their average kinetic energies, and therefore temperatures, equalize.
Carta 272
Domanda
How much heat warms 100.0 g of water by 5.0°C?
Risposta
2.1 kJ. Use q = (100.0 g)(4.184 J g^-1 °C^-1)(5.0°C).
Carta 273
Domanda
How are the molar enthalpies of a phase change and its reverse related?
Risposta
They have equal magnitudes and opposite signs, such as ΔHcond = -ΔHvap and ΔHfreeze = -ΔHfus.
Carta 274
Domanda
How does doubling every coefficient in a thermochemical equation affect ΔH?
Risposta
It doubles ΔH.
Carta 275
Domanda
Why is forming a bond exothermic?
Risposta
Atoms move to a lower-potential-energy bonded arrangement and release energy.
Carta 276
Domanda
What formation equation defines ΔHf° for CO₂(g)?
Risposta
C(s, graphite) + O₂(g) → CO₂(g), forming exactly one mole from elements in standard states.
Carta 277
Domanda
What should happen to intermediate species when equations in a Hess’s law calculation are added?
Risposta
They cancel, leaving the target overall reaction.
Carta 278
Domanda
If the surroundings warm during a process, what is the likely sign of qsystem?
Risposta
Negative; the system likely released heat to the surroundings.
Carta 279
Domanda
For a profile with reactants at 40 kJ and products at 10 kJ, what is ΔH?
Risposta
-30 kJ for the reaction as drawn.
Carta 280
Domanda
Assuming no phase change, what determines the final temperature when two substances exchange heat in an insulated container?
Risposta
Energy conservation: q_warm + q_cool = 0. Use each substance's mass, heat capacity, and initial temperature to solve for the common final temperature.
Carta 281
Domanda
How would heat loss to the room affect an exothermic calorimetry result?
Risposta
The observed temperature rise is too small, so the calculated magnitude of released heat is too low.
Carta 282
Domanda
What heat expression covers warming a liquid without a phase change?
Risposta
q = mcΔT, not nΔHphase.
Carta 283
Domanda
If forming 1 mol of product has ΔH = -50 kJ mol^-1, what is q when 2 mol forms?
Risposta
-100 kJ. Use q = nΔH = (2 mol)(-50 kJ mol^-1).
Carta 284
Domanda
Breaking reactant bonds requires 500 kJ, and forming product bonds releases 650 kJ; what is the estimated ΔH?
Risposta
-150 kJ, from 500 − 650.
Carta 285
Domanda
For CO(g) + ½O₂(g) → CO₂(g), what is ΔH°rxn if ΔHf°[CO] = -110.5 and ΔHf°[CO₂] = -393.5 kJ mol^-1?
Risposta
-283.0 kJ. Use -393.5 - [-110.5 + ½(0)], since ΔHf°[O₂(g)] = 0.
Carta 286
Domanda
In a Hess’s law calculation, two valid steps have ΔH values +25 kJ and -60 kJ; what is the combined ΔH?
Risposta
-35 kJ, provided the equations add to the target reaction.
Carta 287
Domanda
Why is “bonds breaking releases energy” incorrect?
Risposta
Bond breaking absorbs energy; the overall reaction releases energy only when forming new bonds releases more than breaking old bonds requires.
Carta 288
Domanda
How would melting appear on an energy diagram?
Risposta
The liquid lies above the solid, so ΔHfus is positive; the diagram represents a physical, endothermic change.
Carta 289
Domanda
Can two objects at the same temperature exchange energy microscopically?
Risposta
Yes, but their energy transfers balance, so there is no net heat flow.
Carta 290
Domanda
Why must the calorimeter's heat capacity be included when it isn't negligible?
Risposta
The apparatus can absorb or release heat, so include q_cal = C_calΔT in the energy balance: q_process + q_solution + q_cal = 0.
Carta 291
Domanda
What makes chemical equilibrium dynamic?
Risposta
Forward and reverse reactions continue at equal rates even though macroscopic concentrations stay constant.
Carta 292
Domanda
For aA + bB ⇌ cC, what is the concentration-form expression for Q?
Risposta
Q = [C]^c / ([A]^a[B]^b), using current rather than necessarily equilibrium concentrations.
Carta 293
Domanda
What does K much greater than 1 indicate?
Risposta
Products predominate at equilibrium, though K says nothing about reaction speed.
Carta 294
Domanda
How does reversing a reaction change its equilibrium constant?
Risposta
K becomes 1/K.
Carta 295
Domanda
Can a reversible system reach equilibrium when it starts with only products?
Risposta
Yes, if the reverse reaction is possible. The equilibrium composition depends on temperature, initial amounts, and volume or pressure.
Carta 296
Domanda
How do Q and K predict reaction direction?
Risposta
Q < K shifts forward, Q > K shifts reverse, and Q = K means equilibrium.
Carta 297
Domanda
Which species are omitted from a heterogeneous equilibrium expression?
Risposta
Pure solids and pure liquids because their activities are effectively constant.
Carta 298
Domanda
How does increasing a dissolved reactant's concentration or a gaseous reactant's partial pressure affect equilibrium at constant temperature when other Q terms are initially unchanged?
Risposta
It lowers Q relative to K, so the system shifts toward products until Q = K again. Changing the amount of a pure solid or liquid omitted from Q does not cause this shift while that pure phase remains present.
Carta 299
Domanda
What does a flat concentration-time graph mean at equilibrium?
Risposta
Each concentration is constant, not necessarily equal to the others.
Carta 300
Domanda
For A ⇌ B in one fixed volume, a particulate model shows 16 A and 0 B initially, then 4 A and 12 B at equilibrium. What changed, what predominates, and what is Kc?
Risposta
The net change was forward: 12 A particles became 12 B particles. B predominates at equilibrium, and Kc = [B]/[A] = 12/4 = 3.0 because both counts come from the same fixed volume.
Carta 301
Domanda
What can Ksp tell you about a salt's solubility, and when can two Ksp values be compared directly?
Risposta
Ksp > 1 indicates a soluble salt. For salts with the same dissolution stoichiometry, a larger Ksp generally means greater molar solubility; across different stoichiometries, calculate molar solubility before comparing.
Carta 302
Domanda
What is the common-ion effect on solubility?
Risposta
Adding an ion already in the dissolution equilibrium usually decreases the solid's molar solubility.
Carta 303
Domanda
How does uniform dilution shift an aqueous equilibrium based on the stoichiometric powers in Q?
Risposta
It shifts toward the side with the larger sum of stoichiometric coefficients for dissolved species included in Q. If the sums are equal, dilution causes no shift by this effect; pure solids and liquids remain omitted.
Carta 304
Domanda
What happens if a reversible reaction starts with reactants only?
Risposta
The forward rate is initially largest; products form, the reverse rate grows, and the rates eventually become equal.
Carta 305
Domanda
What is the purpose of an ICE table?
Risposta
To organize initial, change, and equilibrium concentrations using reaction stoichiometry.
Carta 306
Domanda
Can a reaction with a very large K be slow?
Risposta
Yes. K describes thermodynamic equilibrium position, while rate depends on kinetics and activation energy.
Carta 307
Domanda
What happens to Q immediately after product concentration increases?
Risposta
Q increases; if it rises above K, the reaction shifts toward reactants.
Carta 308
Domanda
How does multiplying every reaction coefficient by 2 affect K?
Risposta
The new equilibrium constant is K².
Carta 309
Domanda
For A ⇌ B, Kc = 4.0 and initially [A] = 1.0 M and [B] = 0, what are the equilibrium concentrations?
Risposta
[A] = 0.20 M and [B] = 0.80 M. Let x form: Kc = x/(1.0 − x) = 4.0, so x = 0.80 M.
Carta 310
Domanda
What macroscopic properties stay constant at equilibrium?
Risposta
Properties such as concentration, color, and pressure remain constant when external conditions are fixed.
Carta 311
Domanda
How does decreasing volume shift a gaseous equilibrium?
Risposta
Toward the side with fewer moles of gas, if the two sides have different gaseous mole counts.
Carta 312
Domanda
For N₂ + 3H₂ ⇌ 2NH₃, what is Kc?
Risposta
Kc = [NH₃]² / ([N₂][H₂]³).
Carta 313
Domanda
For CaF₂(s) ⇌ Ca²⁺ + 2F⁻, how is Ksp written in terms of molar solubility s in pure water?
Risposta
Ksp = s(2s)² = 4s³ because [Ca²⁺] = s and [F⁻] = 2s.
Carta 314
Domanda
What does K much less than 1 indicate?
Risposta
Reactants predominate at equilibrium.
Carta 315
Domanda
How does decreasing a dissolved product's concentration or a gaseous product's partial pressure affect equilibrium when other Q terms are initially unchanged?
Risposta
It lowers Q and drives a net forward reaction until equilibrium returns. Changing the amount of a pure solid or liquid omitted from Q does not cause this shift while that phase remains.
Carta 316
Domanda
Does equilibrium mean the reaction has stopped?
Risposta
No. Both directions continue, but equal rates produce no net macroscopic change.
Carta 317
Domanda
Why does adding NaF reduce CaF₂ solubility?
Risposta
The added F⁻ raises Qsp, shifting the dissolution equilibrium toward solid CaF₂.
Carta 318
Domanda
For N₂ + 3H₂ ⇌ 2NH₃, what is Kp when P_N₂ = 0.50 atm, P_H₂ = 1.50 atm, and P_NH₃ = 0.25 atm?
Risposta
0.037. Use Kp = (P_NH₃)²/[(P_N₂)(P_H₂)³] = (0.25)²/[(0.50)(1.50)³]. Use equilibrium partial pressures directly; Kc↔Kp conversion isn't assessed.
Carta 319
Domanda
What happens to Q when a gaseous equilibrium mixture is compressed at constant temperature if products have fewer gas moles?
Risposta
Q falls relative to K, so the reaction shifts toward products.
Carta 320
Domanda
How do K and Q transform when a reaction is reversed, its coefficients are multiplied, or reactions are added?
Risposta
They follow the same algebra: reversing takes the reciprocal, multiplying every coefficient by c raises the value to the power c, and adding reactions multiplies their K or Q values.
Carta 321
Domanda
When is the small-x approximation acceptable?
Risposta
When x is small relative to the initial concentration and the final result confirms the neglected change is suitably small.
Carta 322
Domanda
What graph feature shows a disturbance followed by re-equilibration?
Risposta
A sudden or gradual concentration change followed by new constant plateaus while rates return to equality.
Carta 323
Domanda
If Q = 0.20 and K = 5.0, which direction is favored next?
Risposta
Forward, because Q < K.
Carta 324
Domanda
At equilibrium, are reactant and product concentrations equal?
Risposta
Not necessarily. They are constant, while forward and reverse rates are equal.
Carta 325
Domanda
CaF₂ has Ksp = 3.2 × 10^-11 in pure water; what is its molar solubility?
Risposta
2.0 × 10^-4 M. If the molar solubility is s, then [Ca²⁺] = s, [F⁻] = 2s, and Ksp = 4s³.
Carta 326
Domanda
For N₂ + 3H₂ ⇌ 2NH₃, how is Qp written?
Risposta
Qp = (P_NH₃)²/[(P_N₂)(P_H₂)³], using the current partial pressures rather than necessarily equilibrium values.
Carta 327
Domanda
How does heating shift an endothermic forward reaction?
Risposta
Toward products, and K increases because temperature changes the equilibrium constant.
Carta 328
Domanda
Why do both forward and reverse rates change as equilibrium is approached?
Risposta
As reactant and product concentrations change, the collision frequencies for the two directions change until their rates match.
Carta 329
Domanda
CaF₂ has Ksp = 3.2 × 10^-11. What is its molar solubility in 0.10 M NaF?
Risposta
About 3.2 × 10^-9 M. With [F⁻] ≈ 0.10 M, Ksp = [Ca²⁺][F⁻]² gives s = (3.2 × 10^-11)/(0.10)². The common ion lowers solubility but does not change Ksp at constant temperature.
Carta 330
Domanda
What concentration data must be used to calculate Kc?
Risposta
Equilibrium concentrations, each raised to its stoichiometric coefficient and excluding pure solids and liquids.
Carta 331
Domanda
What is a Brønsted–Lowry acid?
Risposta
A proton donor.
Carta 332
Domanda
How is pH defined?
Risposta
pH = -log[H₃O⁺].
Carta 333
Domanda
What is Ka for HA + H₂O ⇌ H₃O⁺ + A⁻?
Risposta
Ka = [H₃O⁺][A⁻]/[HA].
Carta 334
Domanda
How does stabilizing a base affect its basicity and the strength of its conjugate acid?
Risposta
It makes the base weaker and its conjugate acid stronger. A more stable base is less willing to accept H⁺.
Carta 335
Domanda
What is a Brønsted–Lowry base?
Risposta
A proton acceptor.
Carta 336
Domanda
At 25°C, what are Kw and the relationship between pH and pOH?
Risposta
Kw = [H₃O⁺][OH⁻] = 1.0 × 10^-14. Taking negative logarithms gives pH + pOH = 14.00.
Carta 337
Domanda
What is Kb for B + H₂O ⇌ BH⁺ + OH⁻?
Risposta
Kb = [BH⁺][OH⁻]/[B].
Carta 338
Domanda
Why can lowering pH increase the solubility of a salt containing a basic anion?
Risposta
H₃O⁺ consumes the anion, pulling the dissolution equilibrium toward more dissolved ions.
Carta 339
Domanda
What are conjugate acid–base pairs?
Risposta
Species that differ by exactly one proton.
Carta 340
Domanda
What is the pH of 1.0 × 10^-3 M HCl?
Risposta
3.00, assuming complete dissociation and negligible water contribution.
Carta 341
Domanda
How are pKa and pKb defined?
Risposta
pKa = -log Ka, and pKb = -log Kb.
Carta 342
Domanda
Why does acid strength increase across a row of comparable hydrides?
Risposta
Increasing electronegativity stabilizes the conjugate base and polarizes the H–A bond.
Carta 343
Domanda
What is an amphiprotic species?
Risposta
A species that can donate or accept a proton, such as HCO₃⁻.
Carta 344
Domanda
What amounts remain after a limited amount of strong base partially neutralizes weak acid HA?
Risposta
Subtract the reacted moles from HA and form the same number of moles of A⁻. The result gives the remaining HA and formed A⁻ amounts before any equilibrium or buffer-pH calculation.
Carta 345
Domanda
How are Ka, Kb, pKa, and pKb related for a conjugate pair at 25°C?
Risposta
KaKb = Kw = 1.0 × 10^-14, and pKa + pKb = pKw = 14.00.
Carta 346
Domanda
When does pH have little effect on a salt's solubility?
Risposta
When neither dissolved ion reacts appreciably with H₃O⁺ or OH⁻.
Carta 347
Domanda
How does H₂O act in HCl + H₂O → H₃O⁺ + Cl⁻ and in NH₃ + H₂O ⇌ NH₄⁺ + OH⁻?
Risposta
It acts as a base in the first reaction by accepting H⁺, and as an acid in the second by donating H⁺.
Carta 348
Domanda
After mixing weak base B with strong acid, what controls the final solution in the three stoichiometric regimes?
Risposta
Excess B leaves a B/BH⁺ buffer; equimolar amounts leave BH⁺, so the solution is acidic; excess strong acid sets the pH from the remaining H₃O⁺.
Carta 349
Domanda
What two components make a typical weak-acid buffer?
Risposta
A weak acid and a significant amount of its conjugate base.
Carta 350
Domanda
What do the successive half-equivalence pH values approximate in a diprotic weak-acid titration?
Risposta
The first approximates pKa₁ and the second approximates pKa₂ because each conjugate pair has equal concentrations at its half-equivalence point.
Carta 351
Domanda
Which acid is stronger, one with pKa 2 or pKa 5?
Risposta
The acid with pKa 2; lower pKa means larger Ka.
Carta 352
Domanda
What is the Henderson–Hasselbalch equation?
Risposta
pH = pKa + log([A⁻]/[HA]).
Carta 353
Domanda
Why are larger binary hydrides down a group often stronger acids?
Risposta
The H–A bond becomes weaker as the central atom grows, so proton release is easier.
Carta 354
Domanda
What mainly determines buffer capacity?
Risposta
The concentrations of both members of the conjugate acid–base pair. Increasing both concentrations at a fixed ratio increases capacity without changing pH; capacity is best balanced for added acid and base when their concentrations are similar.
Carta 355
Domanda
Why does acid increase CaCO₃ solubility?
Risposta
H₃O⁺ converts CO₃²⁻ to HCO₃⁻ or carbonic acid species, reducing free carbonate and driving more CaCO₃ to dissolve.
Carta 356
Domanda
What does pH < pKa imply for a weak-acid pair?
Risposta
The protonated form HA predominates over A⁻.
Carta 357
Domanda
What happens when stoichiometrically equal amounts of a monoprotic weak acid and strong base are mixed?
Risposta
The weak acid is consumed to its conjugate base; at equivalence, the solution isn't a buffer containing both forms.
Carta 358
Domanda
What is [H₃O⁺] when pH = 4.50?
Risposta
3.2 × 10^-5 M, from [H₃O⁺] = 10^-pH.
Carta 359
Domanda
What is the pH of 0.010 M Ba(OH)₂ at 25°C?
Risposta
About 12.30. Complete dissociation gives [OH⁻] = 0.020 M, so pOH = 1.70. At 25°C, pH + pOH = 14.00, so pH = 12.30.
Carta 360
Domanda
How does a buffer respond to a small amount of added strong acid?
Risposta
Its conjugate base consumes H⁺, converting to the weak acid and limiting the pH change.
Carta 361
Domanda
Why is the equivalence-point solution basic in a monoprotic weak-acid–strong-base titration?
Risposta
The conjugate base produced at equivalence reacts with water to form OH⁻, so the pH is above neutral—above 7.00 at 25°C.
Carta 362
Domanda
How is percent ionization calculated for a weak acid or weak base?
Risposta
For HA, use ([H₃O⁺]equilibrium ÷ [HA]initial) × 100%. For B, use ([BH⁺]equilibrium ÷ [B]initial) × 100%, under the usual monoprotic setup.
Carta 363
Domanda
When is Henderson–Hasselbalch useful for an initial buffer-pH calculation?
Risposta
Use it when both members of a conjugate acid–base pair are present in meaningful amounts, including after in-scope stoichiometry creates a buffer. Calculating the pH change after acid or base is added to an existing buffer is outside this deck’s scope.
Carta 364
Domanda
Why does adding oxygen atoms usually strengthen oxyacids with the same central atom?
Risposta
Extra oxygens withdraw electron density and delocalize negative charge in the conjugate base.
Carta 365
Domanda
A prepared buffer is accidentally diluted to twice its intended volume; what happens to its pH and capacity?
Risposta
Its pH stays nearly the same, and its capacity per liter is halved because both component concentrations halve. The total neutralizing moles in the sample remain unchanged.
Carta 366
Domanda
How does adding OH⁻ affect Mg(OH)₂ solubility?
Risposta
It decreases solubility through the common-ion effect, shifting Mg(OH)₂(s) ⇌ Mg²⁺ + 2OH⁻ toward the solid.
Carta 367
Domanda
A buffer has equal [A⁻] and [HA]; what is its pH?
Risposta
pH = pKa because log(1) = 0.
Carta 368
Domanda
How should a weak acid–strong base mixture be solved before equivalence?
Risposta
First use mole stoichiometry; if both HA and A⁻ remain, use the resulting buffer relation.
Carta 369
Domanda
Why can pure neutral water have a pH other than 7.00?
Risposta
Kw changes with temperature. Neutrality means [H₃O⁺] = [OH⁻], while pH = 7.00 only when Kw = 1.0 × 10^-14 at 25°C.
Carta 370
Domanda
25.0 mL of 0.200 M HCl is diluted to 100.0 mL; what is the pH?
Risposta
1.301. Dilution gives [H₃O⁺] = (0.200 M)(25.0 mL)/(100.0 mL) = 0.0500 M, so pH = -log(0.0500).
Carta 371
Domanda
How does a buffer respond to a small amount of added strong base?
Risposta
The weak acid consumes OH⁻, forming conjugate base and water.
Carta 372
Domanda
How do you find the final pH after mixing a strong acid and strong base at 25°C?
Risposta
Use H₃O⁺ + OH⁻ → 2H₂O and compare their moles. Divide excess H₃O⁺ or OH⁻ by the total volume, then calculate pH or pOH from that excess concentration. Equal moles give pH 7.00 at 25°C.
Carta 373
Domanda
What distinguishes acid strength from acid concentration?
Risposta
Strength is the equilibrium tendency to donate H⁺, reflected by Ka or pKa; concentration is the amount of acid per solution volume.
Carta 374
Domanda
If [A⁻]/[HA] = 10, how does pH compare with pKa?
Risposta
pH = pKa + 1 because log 10 = 1.
Carta 375
Domanda
Which conjugate base is more stable, one with localized or resonance-delocalized charge?
Risposta
The resonance-delocalized conjugate base, which generally corresponds to the stronger acid.
Carta 376
Domanda
Which 1.0 L buffer has greater capacity: 1.0 mol each of HA/A⁻ or 0.10 mol each at the same ratio?
Risposta
The 1.0 mol pair; both have the same initial pH, but the larger amounts neutralize more added acid or base.
Carta 377
Domanda
For BHX(s) ⇌ BH⁺ + X⁻, why can raising pH increase the salt's solubility?
Risposta
OH⁻ consumes BH⁺ to form B and H₂O, so dissolution shifts right to replace BH⁺. This is a qualitative prediction, not a pH-dependent solubility calculation.
Carta 378
Domanda
What does pH > pKa imply for a weak-acid pair?
Risposta
The deprotonated form A⁻ predominates over HA.
Carta 379
Domanda
For HA + B ⇌ A⁻ + BH⁺, which side is favored when pKa(HA) = 4 and pKa(BH⁺) = 9?
Risposta
Products are favored. Proton transfer moves toward the weaker acid–base pair, and K ≈ 10^(9 − 4) = 10^5.
Carta 380
Domanda
What is the pOH when [OH⁻] = 2.5 × 10^-4 M?
Risposta
3.60, from -log(2.5 × 10^-4).
Carta 381
Domanda
What is the pH of 0.100 M HA when Ka = 1.0 × 10^-5?
Risposta
About 3.00. The ICE setup gives Ka = x²/(0.100 − x); x ≈ 1.0 × 10^-3 M, and the 1.0% change validates the approximation.
Carta 382
Domanda
Why does a buffer fail after too much strong acid is added?
Risposta
Its conjugate base is depleted, so added H⁺ is no longer consumed effectively.
Carta 383
Domanda
What do two clear equivalence regions on an acid titration curve suggest?
Risposta
At least two distinguishable titratable protons; on a clean ideal curve with exactly two equivalence regions, this is consistent with a diprotic acid.
Carta 384
Domanda
A buffer has pKa 4.8 and [A⁻]/[HA] = 0.10; what is pH?
Risposta
3.8, from 4.8 + log(0.10).
Carta 385
Domanda
Why is HCl stronger than HF in water despite F being more electronegative?
Risposta
The H–F bond is much stronger; bond strength dominates this down-group binary-acid comparison.
Carta 386
Domanda
Why does percent ionization increase when a weak acid is diluted?
Risposta
Dilution shifts ionization toward more particles, so a larger fraction ionizes even though [H₃O⁺] decreases.
Carta 387
Domanda
A buffer contains more HA than A⁻. Which addition can it neutralize in greater amount: strong acid or strong base?
Risposta
Strong base. The larger HA reserve consumes more added OH⁻; a buffer with more A⁻ than HA instead has greater capacity for added strong acid.
Carta 388
Domanda
Why can removing a basic anion increase a salt's molar solubility without changing Ksp?
Risposta
The equilibrium shifts to replace the consumed ion; Ksp remains fixed at the same temperature.
Carta 389
Domanda
Why can an acid–base indicator change color as pH changes?
Risposta
Its protonated and deprotonated forms have different colors or other observable properties, and their relative amounts change with pH.
Carta 390
Domanda
What buffer results from mixing 1.0 mol HA with 0.40 mol OH⁻?
Risposta
0.60 mol HA and 0.40 mol A⁻ remain, forming a buffer before any equilibrium calculation.
Carta 391
Domanda
What is the pH of 0.200 M weak base B when Kb = 2.0 × 10^-5 at 25°C?
Risposta
About 11.30. The ICE setup gives Kb = x²/(0.200 − x); x ≈ 2.0 × 10^-3 M OH⁻, and the 1.0% change validates the approximation.
Carta 392
Domanda
Why does a weak acid alone not make an effective buffer?
Risposta
It lacks a substantial conjugate-base reserve to consume added strong acid.
Carta 393
Domanda
What controls pH after excess strong base passes equivalence?
Risposta
The concentration of excess OH⁻ after accounting for reaction stoichiometry and total volume.
Carta 394
Domanda
How should an indicator be chosen for a titration?
Risposta
Its color-change range should fall within the steep pH change near the equivalence point.
Carta 395
Domanda
How can a measured pH and known pKa give a conjugate-base/acid ratio?
Risposta
Rearrange Henderson–Hasselbalch: [A⁻]/[HA] = 10^(pH − pKa).
Carta 396
Domanda
Can a weak base and its conjugate acid form a buffer?
Risposta
Yes, when both are present in significant amounts.
Carta 397
Domanda
For equal-volume buffers with the same conjugate-base/acid ratio, how does adding the same amount of strong acid affect a more concentrated versus less concentrated buffer?
Risposta
The concentrated buffer changes pH less because it has greater capacity.
Carta 398
Domanda
How does equivalence-point pH compare for strong acid–strong base, weak acid–strong base, and weak base–strong acid titrations at 25°C?
Risposta
Strong acid–strong base: pH 7.00. Weak acid–strong base: above 7.00 because the conjugate base reacts with water. Weak base–strong acid: below 7.00 because the conjugate acid reacts with water.
Carta 399
Domanda
Why should mole ratios replace concentration ratios after mixing buffer solutions?
Risposta
Both components share the same final volume, so that volume cancels in [A⁻]/[HA].
Carta 400
Domanda
How does adding a little strong acid change a buffer's conjugate-base and conjugate-acid amounts?
Risposta
The conjugate base decreases and its conjugate acid increases by the amount of strong acid consumed.
Carta 401
Domanda
What does entropy measure qualitatively?
Risposta
The dispersal of matter and energy among available microstates.
Carta 402
Domanda
How is standard reaction entropy calculated?
Risposta
ΔS°rxn = ΣνS°(products) − ΣνS°(reactants).
Carta 403
Domanda
What equation gives ΔG° from ΔH° and ΔS°, and what standard states do the degree symbols assume?
Risposta
ΔG° = ΔH° − TΔS°. The standard states are pure substances, 1.0 M solutions, and gases at 1 atm or 1 bar; T is in kelvins and energy units must match.
Carta 404
Domanda
Does thermodynamic favorability guarantee a fast reaction?
Risposta
No. A favorable reaction can be slow when its activation barrier is large.
Carta 405
Domanda
What is ΔG at equilibrium?
Risposta
Zero under the current conditions because there is no net driving force.
Carta 406
Domanda
Why can an endothermic dissolution still be thermodynamically favorable?
Risposta
A sufficiently positive entropy change can make TΔS exceed positive ΔH, giving negative ΔG.
Carta 407
Domanda
How can an unfavorable reaction be driven by a favorable one?
Risposta
Couple them so their equations and ΔG values add to a negative overall ΔG.
Carta 408
Domanda
Where does oxidation occur in every electrochemical cell?
Risposta
At the anode.
Carta 409
Domanda
How are standard cell potential and standard free energy related?
Risposta
ΔG° = -nFE°cell.
Carta 410
Domanda
What equation gives cell potential under nonstandard conditions?
Risposta
E = E° − (RT/nF) ln Q. When Q = 1, ln Q = 0, so E = E°.
Carta 411
Domanda
How is electrical charge related to current and time?
Risposta
q = It.
Carta 412
Domanda
Which phase has greater molar entropy, liquid water or ice at the same temperature?
Risposta
Liquid water because its molecules have more accessible arrangements and motion.
Carta 413
Domanda
Do elements in their standard states have zero standard molar entropy?
Risposta
No. Their ΔHf° is zero, but their absolute S° values are positive above 0 K.
Carta 414
Domanda
How do the four ΔH° and ΔS° sign combinations determine thermodynamic favorability across temperature?
Risposta
ΔH° < 0 and ΔS° > 0 is favorable at every temperature; ΔH° > 0 and ΔS° < 0 is thermodynamically unfavored at every temperature. If both are positive, favorability requires high temperature; if both are negative, it requires low temperature.
Carta 415
Domanda
What does it indicate when a thermodynamically favored process does not occur at a measurable rate?
Risposta
It is under kinetic control, commonly because of a high activation energy; no measurable reaction does not mean the system is at equilibrium.
Carta 416
Domanda
How are ΔG° and K related?
Risposta
ΔG° = -RT ln K.
Carta 417
Domanda
What two contributions compete in dissolving an ionic solid?
Risposta
Enthalpy changes from separating and solvating particles, and entropy changes from their new dispersal and solvent organization.
Carta 418
Domanda
What must cancel when coupled reactions are added?
Risposta
Shared intermediates, leaving the desired net reaction.
Carta 419
Domanda
Where does reduction occur in every electrochemical cell?
Risposta
At the cathode.
Carta 420
Domanda
What sign of E°cell indicates a favorable standard galvanic reaction?
Risposta
Positive E°cell, corresponding to negative ΔG°.
Carta 421
Domanda
If Q increases for a galvanic reaction, how does E change at fixed temperature?
Risposta
E decreases according to the Nernst equation. Le Châtelier's principle does not apply to an operating cell away from equilibrium; use Q and Nernst reasoning instead.
Carta 422
Domanda
How are moles of electrons found from charge?
Risposta
Moles e⁻ = q/F, where F ≈ 96485 C mol^-1 e⁻.
Carta 423
Domanda
How does producing more gas particles usually affect system entropy?
Risposta
It increases entropy because the particles have more positional microstates.
Carta 424
Domanda
Can a dissolution with negative ΔH be unfavorable?
Risposta
Yes. A sufficiently negative entropy change at the stated temperature can make ΔG positive.
Carta 425
Domanda
When can a process with ΔH > 0 and ΔS > 0 become favorable?
Risposta
At sufficiently high temperature, when TΔS exceeds ΔH.
Carta 426
Domanda
How does a catalyst affect ΔG?
Risposta
It does not change ΔG; it lowers the activation barrier for both directions.
Carta 427
Domanda
For A → B, ΔGf°(A) = -50 kJ mol^-1 and ΔGf°(B) = -80 kJ mol^-1. What is ΔG°rxn?
Risposta
-30 kJ mol^-1. Use ΣνΔGf°(products) − ΣνΔGf°(reactants) = -80 − (-50).
Carta 428
Domanda
Why can dissolving a gas in a liquid have a negative entropy change?
Risposta
Gas particles lose much of their translational freedom when confined and solvated in the liquid.
Carta 429
Domanda
If coupled steps have ΔG values +20 kJ and -35 kJ, what is overall ΔG?
Risposta
-15 kJ, so the combined process is thermodynamically favorable under those conditions.
Carta 430
Domanda
What role does each half-cell solution play in an electrochemical cell?
Risposta
It supplies dissolved redox species at an electrode interface and carries ions within its compartment. Separate compartments prevent direct mixing while the external circuit and salt bridge connect the half-cells.
Carta 431
Domanda
How is E°cell found from standard reduction potentials?
Risposta
E°cell = E°cathode − E°anode, using both tabulated values as reductions.
Carta 432
Domanda
How does a cell's potential magnitude change as Q approaches or moves away from K, and what is E at equilibrium?
Risposta
|E| falls toward zero as Q approaches K and grows as the system moves farther from equilibrium. At equilibrium, Q = K and E = 0.
Carta 433
Domanda
How many moles of electrons pass when 1.93 × 10^5 C flows?
Risposta
2.00 mol e⁻, from q/F.
Carta 434
Domanda
How does a salt bridge maintain charge balance in a galvanic cell?
Risposta
Anions migrate toward the anode compartment and cations toward the cathode compartment, countering the net charge imbalances created by the two half-reactions.
Carta 435
Domanda
Why does raising a substance's temperature generally increase its entropy?
Risposta
Energy spreads across more accessible particle energy states, increasing the number of possible microscopic arrangements.
Carta 436
Domanda
When can a process with ΔH < 0 and ΔS < 0 be favorable?
Risposta
At sufficiently low temperature, where the unfavorable -TΔS term is small.
Carta 437
Domanda
Why can diamond persist even though graphite is more stable at standard conditions?
Risposta
Conversion has a large activation barrier, so diamond is kinetically persistent.
Carta 438
Domanda
What do the external circuit and measuring device do in an electrochemical cell?
Risposta
The circuit carries electrons from anode to cathode; a voltmeter measures potential difference, while an ammeter in series measures current.
Carta 439
Domanda
At constant temperature, how does increasing the volume available to a gas affect its entropy?
Risposta
Entropy increases because the gas particles can occupy more positions in the larger space, so more microstates are accessible.
Carta 440
Domanda
How does reversing one coupled reaction affect its ΔG?
Risposta
It reverses the sign of that reaction's ΔG.
Carta 441
Domanda
Why is n required in ΔG° = -nFE°?
Risposta
It is the moles of electrons transferred per balanced reaction, linking charge flow to reaction extent.
Carta 442
Domanda
What makes an electrolytic cell operate?
Risposta
An external power source drives a thermodynamically unfavorable redox reaction; oxidation still occurs at the anode and reduction at the cathode.
Carta 443
Domanda
In an Mⁿ⁺/M concentration cell, which half-cell is the anode: the dilute or concentrated ion solution?
Risposta
The dilute half-cell. Oxidation produces Mⁿ⁺ there, while reduction consumes Mⁿ⁺ in the concentrated half-cell, so electrons flow from dilute to concentrated as the concentrations move toward equality.
Carta 444
Domanda
How is deposited metal mass found from current and time?
Risposta
Find q = It, convert q/F to moles e⁻, use the half-reaction ratio to moles metal, then multiply by molar mass.
Carta 445
Domanda
Given product S° total 500 J mol^-1 K^-1 and reactant total 420 J mol^-1 K^-1, what is ΔS°?
Risposta
+80 J mol^-1 K^-1.
Carta 446
Domanda
How do electrode masses change in a Zn–Cu galvanic cell?
Risposta
The Zn anode loses mass as Zn → Zn²⁺ + 2e⁻, while the Cu cathode gains mass as Cu²⁺ + 2e⁻ → Cu.
Carta 447
Domanda
What is ΔG° when ΔH° = 50 kJ mol^-1, ΔS° = 0.200 kJ mol^-1 K^-1, and T = 300 K?
Risposta
-10 kJ mol^-1, from ΔG° = 50 − (300)(0.200).
Carta 448
Domanda
Why can temperature change a solid's solubility?
Risposta
Temperature changes the balance of ΔH and TΔS, so it changes the free energy of dissolution and the equilibrium constant.
Carta 449
Domanda
What does the size of ΔG° relative to RT imply about K?
Risposta
ΔG° near zero gives K near 1. When |ΔG°| is much larger than RT, K is far from 1: negative ΔG° gives K ≫ 1, while positive ΔG° gives K ≪ 1.
Carta 450
Domanda
Bubbles form at an inert cathode in acidic solution; which half-reaction can explain them?
Risposta
2H⁺ + 2e⁻ → H₂(g). Gas evolution at the cathode can be direct evidence of reduction.

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450 carte