Q: A reaction mixture has $$[CO] = 0.27\ \mathrm{M}$$, $$[H_2$] = 0.49\ \mathrm{M}$$, and $$[CH_3OH] = 0.11\ \mathrm{M} at $$equilibrium for the reaction $$\mathrm{CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)}. $$What is the value of $$K_c$$?

$$K_c = \dfrac{[CH_3OH]}{[CO][H_2$]^2} = \dfrac{0.11}{0.27 \times (0.49)^2$} \approx 1.7$$

Question 1

Which of the following best describes dynamic equilibrium in a chemical reaction?

Accepted Answer

The rates of the forward and reverse reactions are equal.

Question 2

For the reaction $$\mathrm{H_2$(g) + I_2$(g) \rightleftharpoons 2HI(g)}$$, which expression correctly represents the equilibrium constant $$K_c$$?

Accepted Answer

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

Question 3

A reaction mixture initially contains only reactants. As the reaction proceeds toward equilibrium, what happens to the rate of the forward and reverse reactions?

Accepted Answer

The forward rate decreases and the reverse rate increases.

Question 4

Consider the reaction $$\mathrm{N_2$(g) + O_2$(g) \rightleftharpoons 2NO(g)}$$ with $$K_c$$ being a small number. What does this indicate about the position of equilibrium?

Accepted Answer

The reaction favors the reactants.

Question 5

If the equilibrium constant $$K$$ for a reaction is much greater than 1, which of the following is true?

Accepted Answer

The reaction mixture at equilibrium contains mostly products.

Question 6

For the reaction $$\mathrm{2CO(g) \rightleftharpoons CO_2$(g) + C(s)}$$, which species are included in the equilibrium constant expression?

Accepted Answer

Only $$CO(g)$$ and $$CO_2(g$$)$$

Question 7

A reaction mixture has $$[CO] = 0.27\ \mathrm{M}$$, $$[H_2$] = 0.49\ \mathrm{M}$$, and $$[CH_3OH] = 0.11\ \mathrm{M} at $$equilibrium for the reaction $$\mathrm{CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)}. $$What is the value of $$K_c$$?

Accepted Answer

$$K_c = \dfrac{[CH_3OH]}{[CO][H_2$]^2} = \dfrac{0.11}{0.27 	imes (0.49)^2$} \approx 1.7$$

Question 8

If the reaction quotient $$Q is $$less than the equilibrium constant $$K$$, what will happen to the reaction mixture?

Accepted Answer

The reaction will shift to the right, forming more products.

Question 9

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

Accepted Answer

Adding a catalyst.

Question 10

For the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$$, what will happen if more $$NO_2 is $$added to the system at equilibrium?

Accepted Answer

The reaction will shift to the left, producing more $$N_2O_4.$$

Question 11

A reaction is exothermic. According to Le Châtelier’s Principle, what will happen if the temperature is increased?

Accepted Answer

The reaction will shift to the left, forming more reactants.

Question 12

Which of the following statements about heterogeneous equilibria is correct?

Accepted Answer

Only the concentrations of gases and aqueous species are included in the equilibrium constant expression.

Question 13

If the coefficients in a balanced chemical equation are doubled, how does this affect the equilibrium constant $$K$$?

Accepted Answer

The new $$K is $$the original $$K$$ squared.

Question 14

A reaction mixture at equilibrium is disturbed by removing some product. What is the immediate effect on the rates of the forward and reverse reactions?

Accepted Answer

The forward rate increases and the reverse rate decreases.

Question 15

For the reaction $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$, what will happen if the pressure is increased by decreasing the volume?

Accepted Answer

The reaction will shift to the right, toward fewer moles of gas.

Question 16

Given the reaction $$\mathrm{A(g) \rightleftharpoons 2B(g)}$$ with initial concentrations $$[A]_0 = 1.0\ \mathrm{M}$$ and $$[B]_0 = 0.0\ \mathrm{M}$$, and $$K_c = 2.0$$, what is the equilibrium concentration of $$A$$?

Accepted Answer

$$[A] = 0.33\ \mathrm{M}$$

Question 17

Which of the following best explains why the concentrations of reactants and products remain constant at equilibrium?

Accepted Answer

The rates of the forward and reverse reactions are equal.

Question 18

If $$Q \u003e K$$ for a reaction mixture, what must happen for the system to reach equilibrium?

Accepted Answer

The reaction will shift to the left, forming more reactants.

Question 19

Which of the following is a correct application of Le Châtelier’s Principle?

Accepted Answer

Removing a product shifts the equilibrium to the right.

Chapter 16: Chemical Equilibrium – Principles, Calculations, and Applications

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