Kinetics and Equilibrium Review:
1. The reaction rate for a chemical change is best determined by
a.writing a chemical equation.
b.balancing a chemical equation.
c.predicting the ratio of products to reactants.
d.carrying out an experiment.
2. One factor that cannot be adjusted in order to improve a reaction rate is
a.temperature.
b.surface area.
c.nature of the reactant.
d.concentration.
3. An activated complex can best be described as a(n)
a.unstable arrangement of colliding particles that can rearrange to form products.
b.high-energy complex that is stable enough to isolate and characterize.
c.high-energy molecule with strong bonds and a stable structure.
d.stable molecule with a long lifetime.
4. Catalysts affect reaction rates by
a. forming an activated complex with lower energy.
b. broadening the energy barrier.
c. increasing the activation energy.
d. changing the net thermodynamics of the reaction.
5. Two molecules cannot react if there is not enough
a. kinetic energy.
b. pressure.
c. time.
d. volume.
6. A reaction with a faster rate at room temperature
a. is always an exothermic reaction.
b. is always an endothermic reaction.
c. has a small activation energy.
d. has a large activation energy.
7. Draw an energy profile for an exothermic reaction. Label reactants, products, activated
complex, and activation energy.
8. Draw an energy profile of a reaction with and without a catalyst. Compare the two reactants
with respect to the activation energy and the net energy change.
9. Explain the following statements, using collision theory:
a. Gaseous reactants react faster under high pressure than under low pressure.
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b. Ionic compounds react faster when in solution than as solids.
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c. A class of heterogeneous catalysts called surface catalysts work best as a fine powder.
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10.In which of the following reactions, described by the equations below, will an increase in
pressure have no effect on the equilibrium of the system?
a. 2NO 2 ( g ) →
← N 2O4 (g)
b. 2NOCl( g )
→
←
2NO( g ) + Cl 2 ( g )
c. H 2 O( g ) + CO( g )
d. N 2 ( g ) + 3H 2 ( g )
→
←
→
←
H 2 ( g ) + CO 2 ( g )
2NH 3 ( g )
11. At equilibrium, the rate of the forward reaction is ____________________________ the rate of the reverse reaction.
12. Name three ways that chemical equilibrium can be disturbed.
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In the space provided, predict the effect that decreasing pressure would have on each of the
following reaction systems at equilibrium.
13. H 2 ( g ) + Cl 2 ( g )
14. 3O 2 ( g )
→
←
15. CaCo 3 ( s )
→
←
2HCl( g )
2O 3 ( g )
→
←
CaO( s ) + CO 2 ( g )
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____________________________
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16. a. Compare the rates of forward and reverse reactions when equilibrium has been reached.
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b. Describe what happens to the concentrations of reactants and products when chemical
equilibrium has been reached.
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17. Consider the following equilibrium equation:
energy At equilibrium, which reaction will be favored (forward, reverse, or
neither) when
__________________ a. extra CO gas is introduced?
__________________ b. a catalyst is introduced?
__________________ c. the temperature of the system is lowered?
__________________ d. the pressure on the system is increased due to a decrease in the
container volume?
18. A key step in manufacturing sulfuric acid is represented by the following
equation:
2SO 2 ( g ) + O 2 ( g ) →
← 2SO 3 ( g ) + 100 kJ/mol
To be economically viable, this process must yield as much SO3 as possible in the shortest
possible time. You are in charge of this manufacturing process.
a. Would you impose a high pressure or a low pressure on the system? Explain your answer.
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b. To maximize the yield of SO3, should you keep the temperature high or low during the
reaction?
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c. Will adding a catalyst change the yield of SO3?
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Answers: 1d
2c
3a
4a
5a
6c
7
8
9 a. At high pressure, gas molecules are more closely packed and collide more frequently. Thus, more-effective
collisions occur per unit of time.
b. Ions in solution have more freedom of motion than do ions in a solid; therefore, they can collide with one another
more frequently.
c. The fine powder has more surface area on which reactant particles can be absorbed and, in effect, increases the
concentration of the reactants. An increase in concentration increases the number of effective collisions between
reactant particles.
10c 11 equal to 12 change in concentration, pressure, and/or temperature 13 none 14 reverse reaction is favored
15 forward reaction is favored 16a The rate of the forward reaction equals the rate of the reverse reaction.
16b The concentrations of the products and the reactants remain constant. 17a reverse 17b neither direction
17c
forward 17d reverse 18a Impose a high pressure so the reaction that produces fewer gas molecules will be
favored, which is the forward reaction in this case. 18b Keep the temperature low to favor the forward, exothermic
reaction, but not so low as to slow the rate of the forward reaction too much. 18c No, a catalyst does not change the
percentage yield.