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