Question 1

Which of the following best describes a system at dynamic equilibrium?

Accepted Answer

The forward and reverse reactions occur at equal rates, so the concentrations of reactants and products remain constant.

Question 2

For the reaction $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$, which of the following changes will shift the equilibrium to the right according to Le Châtelier's Principle?

Accepted Answer

Increasing the pressure by decreasing the volume of the container.

Question 3

Which of the following is the correct equilibrium constant expression for the reaction $$\mathrm{aA + bB \rightleftharpoons cC + dD}$$?

Accepted Answer

$$K_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}$$

Question 4

A reaction mixture initially contains only reactants. As the reaction proceeds toward equilibrium, what happens to the value of the reaction quotient $$Q$$?

Accepted Answer

$$Q$$ increases until it equals $$K at $$equilibrium.

Question 5

If the equilibrium constant $$K_c$$ for a reaction is much greater than 1, what does this indicate about the position of equilibrium?

Accepted Answer

The products are favored at equilibrium.

Question 6

For the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)}$$, how will increasing the temperature affect the equilibrium if the reaction is exothermic?

Accepted Answer

The equilibrium will shift to the left, favoring the formation of reactants.

Question 7

Which of the following statements about the equilibrium constant $$K_p$$ for a gaseous reaction is correct?

Accepted Answer

$$K_p is $$related to $$K_c by $$the equation $$K_p = K_c(RT$$)^{\Delta n}$$, where $$\Delta n$$ is the change in moles of gas.

Question 8

A chemist is studying the Haber process: $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}. If $$the system is at equilibrium and more $$\mathrm{H_2$} is $$added, what will happen?

Accepted Answer

The equilibrium will shift to the right, producing more $$\mathrm{NH_3$}.$$

Question 9

Which of the following is a correct assumption when using the 'small $$x$$' approximation in equilibrium calculations?

Accepted Answer

If $$K_c is $$very small and the initial concentration is much larger than $$K_c$$, the change in concentration ($$x) $$can be neglected in the denominator.

Question 10

For the reaction $$\mathrm{A(g) \rightleftharpoons B(g) + C(g)}$$, the initial concentration of $$\mathrm{A} is 1.0 M$$, and $$K_c = 0.10. At $$equilibrium, what is the approximate concentration of $$\mathrm{A} if $$the 'small $$x$$' approximation is valid?

Accepted Answer

0.95 M

Question 11

Which of the following changes will NOT affect the value of the equilibrium constant $$K$$ for a given reaction?

Accepted Answer

Changing the concentrations of reactants or products.

Question 12

A reaction has $$K_c = 1.5 	imes 10$$^{-5}$$. Which statement is true about the equilibrium mixture?

Accepted Answer

The reactants are favored at equilibrium.

Question 13

In a closed container, the following reaction is at equilibrium: $$\mathrm{2NO_2(g) \rightleftharpoons N_2O_4(g)}. $$What will happen if the volume of the container is decreased?

Accepted Answer

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

Question 14

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

Accepted Answer

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

Question 15

For the reaction $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)}$$, the equilibrium concentrations are $$[H_2$] = 0.10 M$$, $$[I_2$] = 0.10 M$$, and $$[HI] = 0.20 M. $$What is the value of $$K_c$$?

Accepted Answer

$$K_c = \frac{[HI]^2}{[H_2$][I_2$]} = \frac{(0.20)^2$}{(0.10)(0.10)} = 4.0$$

Question 16

A reaction mixture has $$Q = 5.0$$ and $$K = 2.0. $$Which direction will the reaction proceed to reach equilibrium?

Accepted Answer

The reaction will proceed to the left (toward reactants).

Question 17

Which of the following is true about the effect of temperature on the equilibrium constant $$K$$?

Accepted Answer

Increasing temperature increases $$K$$ for an endothermic reaction.

Question 18

In the Haber-Bosch process for ammonia production, why is a compromise temperature used rather than the highest possible temperature?

Accepted Answer

A high temperature increases the rate but decreases the yield of ammonia due to the exothermic nature of the reaction.

Question 19

For the reaction $$\mathrm{CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)}$$, what will happen to the equilibrium if $$\mathrm{CH_3OH} is $$removed from the system?

Accepted Answer

The equilibrium will shift to the right to produce more $$\mathrm{CH_3OH}.$$

Chemical Equilibrium and Le Châtelier’s Principle

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