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