Reaction Rates and Chemical EquilibriumTest


True/False

  1. Increasing the temperature of a reaction always increases the rate of reaction.

  2. Reactions often occur in a series of steps called a "mechanism."

  3. The rate of a reaction depends on the rate of the slowest step in its mechanism.

  4. The activated complex is a low-energy, stable molecule that is formed as an intermediate step in a chemical reaction.

  5. Increasing the temperatuare of a reaction speeds up a reaction by lowering the activation energy.

  6. A catalyzed reaction follows the same mechanism as an uncatalyzed reaction.

    A burning candle reaches an identifiable state of chemical equilibrium.

  7. Temperature almost never influences the equilibrium of a reaction.

  8. For the reaction, m A + n B p C + q D, the numerator of the equilibrium constant is [C]p [D]q

  9. Increasing the temperature of the reaction, H2O (g) + C (s) + 31.4 Kcal CO (g) + H2 (g), would be a way to make more products.

  10. A catalyzed reactrion usually produces more products than an uncatalyzed reaction.

  11. If the solubility of PbCrO4 is 1.0 x 10 -4, the Ksp is 1.0 x 10 -2.

  12. Equilibrium tends to favor the side of the reaction with the least amount of randomness.

Multiple Choice (Choose the best answer.)


  1. Reaction rates are affected by concentration, collision geometry, and the presence of a catalyst. Which one of the following statements is FALSE?

    Larger concentrations of reacting particles increases the number of collisions.

    Molecules that do not collide in the correct orientation lower the reaction rate.

    The slowest step in the mechanism determines the rate.

    A catalyst increases the speeds of the reacting particles.

    A catalyst lowers the activation energy of a reaction.

    Use the potential energy diagram below to answer questions 3 - 7.

  2. What is the potential energy of the products?

    150

    200

    250

    350

    450

  3. What is the activation energy of the reaction?

    150

    200

    250

    350

    450

  4. What is the potential energy of the activated complex?

    150

    200

    250

    350

    450

  5. What is the heat of reaction?

    150

    200

    250

    350

    450

  6. The reaction is:

    catalyzed.

    uncatalyzed.

    endothermic.

    exothermic.

    None of the above.

    Use the catalyzed reaction mechanism for the decomposition of HCO2H below to answer questions 8 - 10.

    I. HCO2H + H+ HCO2H2+ (Fast)
    II. HCO2H2+ HCO+ + H2O (Slow)
    III. HCO+ CO + H+ (Fast)

  7. What is the over-all reaction for the mechanism above?

    HCO2H + H+ H2O + CO + H+

    HCO2H2+ CO + H2O + H+

    HCO2H H2O + CO

    HCO2H2+ HCO+ + H2O

    None of the above.

  8. What could be the catalyst?

    HCO2H

    H+

    HCO2H2+

    HCO+

    CO

  9. Which step is rate-determining?

    I

    II

    III

    I and III are both rate-determining.

    It is impossible to tell from the information given.

    You studied the reaction, Fe3+ + SCN- FeSCN2+ + Energy. Which of the following would shift the equilibrium to the reactants?
    Inrease [ Fe3+].

    Remove energy.

    Decrease [SCN-].

    Add energy.

    More than one of these would shift the equilibrium left.

  10. What would would be the result of increasing the pressure by decreasing the volume on the reaction:

    4 NH3 (g) + 5 O2 (g) 4 NO (g) + 6 H2O (g)

    The equilibrium would shift to the products.

    The equilibrium would shift to the reactants.

    The equilibrium would shift both directions.

    The equilibrium would not change.

    It is impossible to tell with the information given.

  11. An equilibrium constant much larger than one indicates:

    a reaction that makes lots of products.

    a reaction that does not make many products.

    a reaction that reaches equilibrium quickly.

    a reaciton that takes a long time to reach equilibrium.

    a reaction that is does not achieve equilibrium.

  12. In the following reaction at equilibrium, the concentration of each substance is [ A ] = 2 M; [B] = 2 M; [C] = 2 M; [D] = 1 M. What is the value of Keq, (the equilibrium constant)?

    2 A + B 3 C + 2 D

    0.50

    0.75

    1.0

    1.3

    5.0

  13. If in the reaction in problem 5 "A" and "C" were both solids, while "B" and "D" were both aqueous, the value of the equilibrium constant wold be:

    0.50

    0.75

    1.0

    1.3

    5.0

  14. The Ksp expression for the reaction BaF2(s) dissolving ( BaF2(s) Ba2+ (aq) + 2 F- (aq) ) woud be:

    Ksp = [Ba2+][F-]2

    Ksp = [Ba2+][2 F-]2

    Ksp =[Ba2+][2 F-]

    Ksp = [Ba2+][F-]2 / [BaF2]

    Ksp = [BaF2] / {[Ba2+][F-]2}

  15. If the Ksp for the reaction in 7 was 1.0 x 10 -6, the solubility of BaF2 (s) is:

    1.0 x 10 -6

    1.0 x 10 -3

    6.3 x 10 -3

    1.0 x 10 -2

    None of these.

  16. Examine the reaction, 3 H2 (g) + N2 (g) 2 NH3 (g) + 22 Kcal, in terms of enthalpy (energy) and entropy (randomness).

    Energy favors products while randomness favors reactants.

    Energy favors products and randomness favors products.

    Energy favors reactants and randomness favors reactants.

    Energy favors reactants while randomness favors products.

    It is impossible to analyze the reaction with the information given.

Problem Solving (Show All Work. Use significant figures.)

1. In mixture 4 in the Rate of Reaction lab, you diluted 5.0 mL of 0.20 M KI solution by adding 15 mL of distilled water. What was the concentration of the KI solution after adding the water?

2. If it took 45 seconds for the clock reaction in the Rate of Reaction lab to turn blue at 25 oC, how long would you predict the reaction would take at 15 oC? Explain your reasoning.



The questions below are based on the following reaction, which takes place in a closed container:

NO (g) + NO2 (g) N2O3 (g) + 9.6 Kcal


3. How does the rate of the forward reaction compare with the rate of the reverse reaction at equilibrium?





4. What effect does a catalyst have on the rate of the forward and reverse reactions? Explain.




5. Compare the equilibrium concentration of N2O3 (g) without a catalyst to its equilibrium concentration with a catalyst. Explain.

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