Q: For the reaction $$\mathrm{A(g) + B(g) \rightleftharpoons C(g)}$$, the initial concentrations are $$[A] = 1.0 M$$, $$[B] = 2.0 M$$, $$[C] = 0 M. At $$equilibrium, $$[C] = 0.5 M. $$What is $$K_c$$?

$$K_c = \frac{0.5}{0.5 \times 1.5}$$

Question 1

Which of the following best describes chemical equilibrium in a closed system?

Accepted Answer

The rates of the forward and reverse reactions are equal.

Question 2

For the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$$, which of the following statements is TRUE at equilibrium?

Accepted Answer

The concentrations of $$\mathrm{N_2O_4}$$ and $$\mathrm{NO_2$}$$ remain constant.

Question 3

Given the reaction $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)}$$, the equilibrium constant expression $$K_c is$$:

Accepted Answer

$$K_c = \frac{[HI]^2}{[H_2$][I_2$]}$$

Question 4

For the reaction $$\mathrm{$$CaCO_3$$(s) \rightleftharpoons CaO(s) + CO_2$(g)}$$, what is the correct equilibrium constant expression ($$K_p) in $$terms of pressure?

Accepted Answer

$$K_p = P_{CO_2$}$$

Question 5

A reaction has $$K_c = 1.2 	imes 10^5$ at a certain temperature. Which statement is correct?

Accepted Answer

The reaction mixture at equilibrium contains mostly products.

Question 6

For the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)}$$, how will the equilibrium shift if the pressure is increased by decreasing the volume?

Accepted Answer

The equilibrium will shift toward the side with fewer moles of gas.

Question 7

Which of the following changes will increase the yield of ammonia in the Haber process ($$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$; $$\Delta H = -92 kJ$$)?

Accepted Answer

Increasing the pressure.

Question 8

If $$K_c$$ for a reaction is $$0.001 at a $$certain temperature, which of the following is true?

Accepted Answer

The reaction favors the formation of reactants.

Question 9

For the reaction $$\mathrm{A(g) + B(g) \rightleftharpoons C(g)}$$, the initial concentrations are $$[A] = 1.0 M$$, $$[B] = 2.0 M$$, $$[C] = 0 M. At $$equilibrium, $$[C] = 0.5 M. $$What is $$K_c$$?

Accepted Answer

$$K_c = \frac{0.5}{0.5 	imes 1.5}$$

Question 10

Which of the following best explains the effect of a catalyst on a system at equilibrium?

Accepted Answer

A catalyst increases the rate at which equilibrium is achieved.

Question 11

For the reaction $$\mathrm{CO_2$(g) + H_2$(g) \rightleftharpoons H_2O(g) + CO(g)}$$, a mixture initially contains $$1.443$$ mol $$CO_2$$, $$0.883$$ mol $$H_2$$, and $$0.222$$ mol $$H_2O in a$$ $$7.50 L $$vessel. At equilibrium, $$1.025$$ mol $$H_2O is $$present. What is the equilibrium concentration of $$CO_2$$?

Accepted Answer

$$[CO_2$] = \frac{1.443 - 0.803}{7.50}$$

Question 12

If $$Q_c \u003c K_c$$ for a reaction mixture, what will happen as the system moves toward equilibrium?

Accepted Answer

The reaction will shift toward the products.

Question 13

Which of the following is TRUE for a heterogeneous equilibrium involving a solid and a gas?

Accepted Answer

Only the concentration (or pressure) of the gas appears in the equilibrium expression.

Question 14

For the reaction $$\mathrm{2NO_2(g) \rightleftharpoons N_2O_4(g)}$$, what will happen if the temperature is decreased, given that the reaction is exothermic?

Accepted Answer

The equilibrium will shift to the right, favoring $$\mathrm{N_2O_4}.$$

Question 15

Which equation correctly relates $$K_p$$ and $$K_c$$ for a reaction involving gases?

Accepted Answer

$$K_p = K_c(RT$$)^{\Delta n}$$

Question 16

A solution initially contains $$1.00 mM of $$protein X and $$1.00 mM of $$protein Y. At equilibrium, $$0.20 mM of $$each remains unbound. What is the equilibrium concentration of the complex XY?

Accepted Answer

$$[XY] = 0.80 mM$$

Question 17

Which of the following is a correct statement about the effect of temperature on the equilibrium constant $$K$$?

Accepted Answer

The value of $$K$$ increases for endothermic reactions as temperature increases.

Question 18

For the reaction $$\mathrm{A(g) + B(g) \rightleftharpoons C(g)}$$, doubling the concentration of A will:

Accepted Answer

Shift the equilibrium to the right.

Chemical Equilibrium: Principles, Calculations, and Applications

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