Q: For the reaction $$CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)$$, $$K_c = 10.2 at 500 K. If $$the initial concentrations are $$[CO] = 0.50\,M$$, $$[H_2$] = 1.00\,M$$, and $$[CH_3OH] = 0.10\,M$$, what is the value of the reaction quotient $$Q_c$$ and in which direction will the reaction proceed to reach equilibrium?

$$Q_c = \frac{[CH_3OH]}{[CO][H_2$]^2} = \frac{0.10}{0.50 \times (1.00)^2$} = 0.20$$; the reaction will proceed to the right (toward products).

Q: A reaction mixture at equilibrium contains $$[A] = 0.20\,M$$, $$[B] = 0.30\,M$$, and $$[C] = 0.40\,M$$ for the reaction $$A(g) + 2B(g) \rightleftharpoons C(g). $$What is the value of $$K_c$$?

$$K_c = \frac{[C]}{[A][B]^2} = \frac{0.40}{0.20 \times (0.30)^2$} = 22.2$$

Question 1

For the reaction $$\mathrm{N_2O_4(g) ightleftharpoons 2NO_2(g)}$$, the equilibrium constant $$K_c at 25$$°C is $$4.6 	imes 10$$^{-3}$$. Which of the following statements best describes the composition of the equilibrium mixture?

Accepted Answer

The mixture contains mostly $$N_2O_4$$ with very little $$NO_2.$$

Question 2

Given the reaction $$2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)$$, write the correct expression for the equilibrium constant $$K_c.$$

Accepted Answer

$$K_c = \frac{[SO_3$]^2}{[SO_2$]^2[O_2$]}$$

Question 3

For the reaction $$H_2(g$$) + $$I_2(g$$) \rightleftharpoons 2HI(g)$$, the equilibrium concentrations are $$[$$H_2$$] = 0.10\,M$$, $$[$$I_2$$] = 0.10\,M$$, and $$[HI] = 0.60\,M$$. Calculate the value of K_c$.

Accepted Answer

$$K_c = \frac{[HI]^2}{[H_2$][I_2$]} = \frac{(0.60)^2$}{(0.10)(0.10)} = 36$$

Question 4

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

Accepted Answer

Changing the concentrations of reactants or products.

Question 5

For the reaction $$CO(g) + 2H_2(g) \rightleftharpoons CH_3OH(g)$$, $$K_c = 10.2 at 500 K. If $$the initial concentrations are $$[CO] = 0.50\,M$$, $$[H_2$] = 1.00\,M$$, and $$[CH_3OH] = 0.10\,M$$, what is the value of the reaction quotient $$Q_c$$ and in which direction will the reaction proceed to reach equilibrium?

Accepted Answer

$$Q_c = \frac{[CH_3OH]}{[CO][H_2$]^2} = \frac{0.10}{0.50 	imes (1.00)^2$} = 0.20$$; the reaction will proceed to the right (toward products).

Question 6

Which of the following statements about heterogeneous equilibria is correct?

Accepted Answer

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

Question 7

For the reaction $$N_2(g) + 3H_2(g$$) \rightleftharpoons 2NH_3(g)$$, K_p$ and K_c$ are related by the equation K_p = K$$_$$c(RT)^{\Delta n}. $$What is the value of $$\Delta n$$ for this reaction?

Accepted Answer

$$\Delta n = 2 - (1 + 3) = -2$$

Question 8

A reaction mixture at equilibrium contains $$[A] = 0.20\,M$$, $$[B] = 0.30\,M$$, and $$[C] = 0.40\,M$$ for the reaction $$A(g) + 2B(g) \rightleftharpoons C(g). $$What is the value of $$K_c$$?

Accepted Answer

$$K_c = \frac{[C]}{[A][B]^2} = \frac{0.40}{0.20 	imes (0.30)^2$} = 22.2$$

Question 9

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

Accepted Answer

The mixture contains mostly products.

Question 10

For the reaction $$2NO_2(g) ightleftharpoons N_2O_4(g)$$, $$K_c = 4.6 	imes 10$$^{-3}$$ at 25°C. If $$[$$NO_2$$] = 0.10\,M$$ and $$[N_2O_4] = 0.50\,M$$, is the system at equilibrium? If not, in which direction will the reaction proceed?

Accepted Answer

$$Q_c = \frac{[N_2O_4]}{[NO_2$]^2} = \frac{0.50}{(0.10)^2$} = 50$$; $$Q_c \u003e K_c$$, so the reaction will proceed to the left (toward reactants).

Question 11

Which of the following is a correct statement regarding the use of activities in equilibrium constant expressions?

Accepted Answer

The activity of a pure solid or pure liquid is taken as 1 and is not included in the equilibrium expression.

Question 12

Consider the following two reactions:

1) $$A \rightleftharpoons B$$, $$K_1

2$$) $$2A \rightleftharpoons 2B$$, $$K_2$$

What is the relationship between $$K_1$$ and $$K_2$$?

Accepted Answer

$$K_2$$ = ($$K_1)^2$

Question 13

A chemist mixes $$0.10$$ mol of $$CO_2(g$$)$$, 0.10$ mol of CO(g$$)$$, and 0.10$ mol of O_2$(g) in a$$ $$1.0 L $$vessel at $$1000 K. $$For the reaction $$CO_2(g$$) + $$H_2(g$$) \rightleftharpoons CO(g) + H_2O(g)$$, K_c = 0.64$ at 1000$ K. If $$[$$H_2$$] = 0.10$$ M and $$[H_2O] = 0.10$$ M, is the system at equilibrium?

Accepted Answer

$$Q_c = \frac{[CO][H_2O]}{[CO_2$][H_2$]} = \frac{0.10 	imes 0.10}{0.10 	imes 0.10} = 1$$; $$Q_c \u003e K_c$$, so the reaction will proceed to the left.

Question 14

For the reaction $$2SO_2(g) + O_2$(g) ightleftharpoons 2SO_3(g)$$, if the equilibrium constant $$K_c is$$ $$1.5 	imes 10^5$ at 700 K, what does this indicate about the position of equilibrium?

Accepted Answer

The reaction mixture contains mostly $$SO_3 at $$equilibrium.

Question 15

If the equilibrium constant for a reaction is $$K = 1.0 	imes 10$$^{-8}$$, which of the following best describes the reaction at equilibrium?

Accepted Answer

The reaction mixture contains mostly reactants.

Question 16

For the reaction $$H_2(g$$) + $$I_2(g$$) \rightleftharpoons 2HI(g)$$, if the equilibrium constant K_c$ is 50$ at a certain temperature, what is the value of K_c$ for the reverse reaction?

Accepted Answer

$$K_c = 1/50 = 0.02$$

Question 17

A reaction has $$K_c = 1.0 	imes 10^3$ at 298 K. If the initial concentrations are $$[A] = 1.0\,M$$, $$[B] = 1.0\,M$$, and $$[C] = 0.01\,M$$ for the reaction A(g) + B(g$$) ightleftharpoons C(g)$$, what will happen as the system moves toward equilibrium?

Accepted Answer

The concentration of $$C$$ will increase as the reaction proceeds to the right.

Question 18

Which of the following is true regarding the effect of a catalyst on the equilibrium constant $$K$$?

Accepted Answer

A catalyst has no effect on the value of $$K.$$

Chapter 15: Chemical Equilibrium – Study Notes

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