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