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 $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$, which of the following changes will shift the equilibrium toward the formation of more $$\mathrm{NH_3$}$$ according to Le Châtelier’s principle?

Accepted Answer

Removing $$\mathrm{NH_3$}$$ from the system

Question 3

Given the equilibrium $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$$, write the correct equilibrium constant expression $$K_c.$$

Accepted Answer

$$K_c = \dfrac{[NO_2$]^2}{[N_2O_4]}$$

Question 4

A reaction mixture at equilibrium contains $$[NO_2$] = 1.45\ \mathrm{M}$$ and $$[N_2O_4] = 9.91\ \mathrm{M}. $$Calculate $$K_c$$ for $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}.$$

Accepted Answer

$$K_c = 0.212$$

Question 5

Which of the following statements about equilibrium constants is TRUE?

Accepted Answer

Equilibrium constants change with temperature.

Question 6

For the reaction $$\mathrm{2NOBr(g) \rightleftharpoons 2NO(g) + Br_2$(g)}$$, if the initial concentration of $$\mathrm{NOBr} is$$ $$3.0\ \mathrm{M}$$ and $$K_c = 7.0$$, what is the equilibrium concentration of $$\mathrm{NO}$$?

Accepted Answer

$$2.6\ \mathrm{M}$$

Question 7

Which of the following will NOT affect the position of equilibrium for a reaction involving only gases?

Accepted Answer

Adding a catalyst

Question 8

For the reaction $$\mathrm{CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)}$$, a vessel contains $$0.0406$$ mol $$\mathrm{CH_3OH}$$, $$0.170$$ mol $$\mathrm{CO}$$, and $$0.302$$ mol $$\mathrm{H_2$} in$$ $$2.00 L at$$ $$500\ \mathrm{K}. $$Calculate $$K_c.$$

Accepted Answer

$$K_c = 1.98$$

Question 9

If the reaction quotient $$Q$$ for a system is less than $$K_c$$, which way will the reaction proceed to reach equilibrium?

Accepted Answer

The reaction will proceed in the forward direction.

Question 10

For the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)}$$, what effect will increasing the pressure have on the equilibrium position?

Accepted Answer

Shift toward products

Question 11

Which of the following is the correct relationship between $$K_p$$ and $$K_c$$ for a reaction where $$\Delta n = 2$$?

Accepted Answer

$$K_p = K_c(RT)^2$

Question 12

A closed system initially contains $$0.30\ \mathrm{M}$$ $$\mathrm{H_2$}$$ and $$0.20\ \mathrm{M}$$ $$\mathrm{I_2$}. At $$equilibrium, the concentration of $$\mathrm{HI} is$$ $$0.37\ \mathrm{M}. $$What is the value of $$K_c$$ for $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)}$$?

Accepted Answer

$$K_c = 79$$

Question 13

Which of the following best explains why pure solids and liquids are not included in equilibrium constant expressions?

Accepted Answer

Their concentrations are constant and do not affect the equilibrium.

Question 14

For the reaction $$\mathrm{2NO(g) + O_2$(g) \rightleftharpoons 2NO_2(g)}$$, if $$K_c is $$very large, what does this indicate about the equilibrium mixture?

Accepted Answer

Mostly products are present.

Question 15

Which of the following is a correct application of Le Châtelier’s principle to a real-world scenario?

Accepted Answer

Drying clothes faster on a windy day due to removal of water vapor.

Question 16

A catalyst is added to a reaction at equilibrium. What effect does this have?

Accepted Answer

It increases the rate at which equilibrium is achieved.

Question 17

For the reaction $$\mathrm{C(s) + CO_2$(g) \rightleftharpoons 2CO(g)}$$ with $$K_c = 5$$, if excess $$\mathrm{C} is $$allowed to react with $$1.25$$ mol $$\mathrm{CO_2$} in a$$ $$1.00 L $$vessel, what is the equilibrium concentration of $$\mathrm{CO}$$?

Accepted Answer

$$2.24\ \mathrm{M}$$

Question 18

Which of the following reactions will have its equilibrium position shifted toward products if the pressure is increased?

Accepted Answer

$$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$

Question 19

For the reaction $$\mathrm{2NO(g) + 2H_2(g) \rightleftharpoons 2H_2O(g) + N_2$(g)}$$, what will happen if the volume of the reaction mixture is reduced at constant temperature?

Accepted Answer

The equilibrium will shift toward products.

Chapter 15: Chemical Equilibrium – Core Concepts and Problem-Solving Strategies

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