Aim to answer every question before checking. Missed questions point you to the sections you need most.
1. (6.1) Chemical equilibrium is:
D. Reactions continue at the molecular level, but net change is zero. Concentrations stay constant even as individual molecules keep interconverting.
2. (6.1) At equilibrium, concentrations of reactants and products:
C. "Equilibrium" does not mean "equal." The ratio set by K can favor either side.
3. (6.2) For the reaction aA + bB ⇌ cC + dD, the equilibrium expression is:
B. Products over reactants, each raised to its stoichiometric coefficient.
4. (6.2) Pure solids and pure liquids in an equilibrium expression:
A. Their concentrations do not change in a meaningful way, so they drop out of K. Gases and dissolved species carry the expression.
5. (6.3) If K is very large (K >> 1):
D. K is dimensionless; large K means [products] at equilibrium is high relative to [reactants]. This says nothing about the speed.
6. (6.3) Kp (partial pressures) and Kc (concentrations) for a gas-phase reaction relate by:
C. When Δ
ngas = 0, Kp = Kc.
7. (6.4) The reaction quotient Q:
B. Comparing Q to K predicts direction: Q < K → forward shift; Q = K → at equilibrium; Q > K → reverse shift.
8. (6.4) If Q < K for a reaction:
A. The ratio of products to reactants is too small relative to K, so the system makes more products to reach K.
9. (6.5) Le Chatelier's principle says:
D. Apply this to concentration, volume/pressure, and temperature changes to predict shifts qualitatively.
10. (6.5) Adding more reactant to an equilibrium system:
C. Q falls below K instantaneously, so the forward reaction proceeds until Q = K again.
11. (6.6) Adding product to an equilibrium system:
B. Q > K momentarily; reverse reaction is favored until Q = K.
12. (6.6) Removing a product from an equilibrium system:
A. Industrial processes (e.g., Haber-Bosch) continuously remove product to drive the reaction forward.
13. (6.7) Increasing total pressure on a gas-phase equilibrium (by decreasing volume) shifts equilibrium:
D. The system reduces pressure by forming fewer gas molecules. No shift occurs when Δ
ngas = 0.
14. (6.7) Adding an inert gas to an equilibrium system at constant volume:
C. Only the partial pressures of reacting gases matter. Inert gas raises total pressure but not partial pressures in a fixed-volume container.
15. (6.8) Raising the temperature of an equilibrium:
B. Add "heat" to the side where it belongs (reactant or product) and apply Le Chatelier.
16. (6.8) Temperature is the only disturbance that:
A. Concentration and pressure changes shift the equilibrium without changing K. Temperature changes K itself.
17. (6.9) A catalyst in an equilibrium system:
D. Catalysts lower Ea equally for the forward and reverse reactions, leaving K unchanged.
18. (6.9) Catalysts affect Ea of:
C. The energy difference between reactants and products (and thus K) is untouched; only the barrier height drops.
19. (6.10) The solubility product Ksp applies to:
B. Ksp = [ion product] at saturation. Low Ksp = low solubility. Precipitates form if the ion product exceeds Ksp.
20. (6.10) For AgCl(s) ⇌ Ag⁺(aq) + Cl⁻(aq), if molar solubility is s, then Ksp equals:
A. For 1:1 salt, Ksp = s × s = s². For MX₂ salts, Ksp = 4s³; for MX₃, Ksp = 27s⁴.
21. (6.11) The common ion effect describes:
D. A direct application of Le Chatelier. Common ion effect is also important in buffer chemistry (weak acid + its conjugate base).
22. (6.11) Adding NaCl to saturated AgCl solution:
C. Ksp does not change; [Ag⁺] at equilibrium falls because [Cl⁻] rises.
23. (6.12) An ICE table is used to:
B. Pair the ICE table with the equilibrium expression to solve for unknown equilibrium concentrations.
24. (6.12) In an ICE table, if x mol/L of reactant is consumed:
A. The "C" row of the ICE table is just stoichiometry applied to x, written with signs that reflect whether each species is consumed or produced.
