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