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