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 $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)}$$, and the equilibrium concentrations $$[\mathrm{H_2$}] = 0.065\,M$$, $$[\mathrm{I_2$}] = 1.065\,M$$, $$[\mathrm{HI}] = 1.87\,M$$, calculate $$K_c.$$

Accepted Answer

$$K_c = \dfrac{[HI]^2}{[H_2$][I_2$]} = \dfrac{(1.87)^2$}{(0.065)(1.065)} = 50.5$$

Question 4

Which of the following changes will shift the equilibrium position of the reaction $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)} to $$the right (toward more ammonia) according to Le Chatelier’s Principle?

Accepted Answer

Removing ammonia as it forms.

Question 5

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

Accepted Answer

$$K_p = \dfrac{P_{CO_2$}}{1}$$

Question 6

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 reactants.

Question 7

Which of the following best explains why a catalyst does NOT affect the equilibrium position of a reaction?

Accepted Answer

A catalyst increases the rate of both the forward and reverse reactions equally.

Question 8

For the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)}$$, how will decreasing the volume of the container affect the equilibrium?

Accepted Answer

The equilibrium will shift to the right, toward more $$\mathrm{SO_3$}.$$

Question 9

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

Accepted Answer

$$[CO_2$] = \dfrac{1.443 - (1.025 - 0.222)}{7.50} = 0.086\,M$$

Question 10

Which of the following is TRUE regarding the effect of temperature on the equilibrium constant $$K$$?

Accepted Answer

The value of $$K$$ depends on whether the reaction is exothermic or endothermic.

Question 11

For the reaction $$\mathrm{A(g) + B(g) \rightleftharpoons C(g) + D(g)}$$, the equilibrium constant $$K_c is $$given by:

Accepted Answer

$$K_c = \dfrac{[C][D]}{[A][B]}$$

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 to the right, forming more products.

Question 13

Which of the following is NOT included in the equilibrium constant expression for a heterogeneous equilibrium?

Accepted Answer

Concentration of a pure solid.

Question 14

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

Accepted Answer

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

Question 15

Which of the following correctly relates $$K_p$$ and $$K_c$$ for the reaction $$aA(g) + bB(g) \rightleftharpoons dD(g) + eE(g)$$?

Accepted Answer

$$K_p = K_c (RT$$)^{\Delta n}$$, where $$\Delta n = (d + e) - (a + b)$$

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 constant $$K_c$$ for the binding reaction $$\mathrm{X(aq) + Y(aq) \rightleftharpoons XY(aq)}$$?

Accepted Answer

$$K_c = \dfrac{[XY]}{[X][Y]} = \dfrac{0.80}{0.20 	imes 0.20} = 20$$

Question 17

Which of the following best describes the effect of adding a catalyst to a reaction at equilibrium?

Accepted Answer

The equilibrium is reached faster, but the equilibrium concentrations remain unchanged.

Chemical Equilibrium: Principles, Calculations, and Applications

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