Q: What happens to the equilibrium constant $$K if $$the direction of a chemical equation is reversed?

$$K is $$inverted ($$K_{\text{new}} = 1/K_{\text{original}}).$$

Q: A reaction mixture at equilibrium contains $$[A] = 0.2\ \mathrm{M}$$, $$[B] = 0.5\ \mathrm{M}$$, and $$[C] = 0.1\ \mathrm{M}$$ for the reaction $$A(g) + 2B(g) \rightleftharpoons 3C(g). $$What is the value of the equilibrium constant $$K$$?

$$K = \frac{[C]^3}{[A][B]^2} = \frac{(0.1)^3$}{0.2 \times (0.5)^2$}$$

Question 1

For the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$$, the equilibrium constant $$K is $$given by $$K = \frac{[NO_2$]^2}{[N_2O_4]}. If$$ $$K \u003e 1$$, what does this indicate about the position of equilibrium?

Accepted Answer

The equilibrium favors the products.

Question 2

If the equilibrium constant for a reaction is $$K = 2.5 	imes 10$$^{-5}$$, what can you conclude about the relative concentrations of products and reactants at equilibrium?

Accepted Answer

Reactants are favored over products.

Question 3

What happens to the equilibrium constant $$K if $$the direction of a chemical equation is reversed?

Accepted Answer

$$K is $$inverted ($$K_{	ext{new}} = 1/K_{	ext{original}}).$$

Question 4

Given the following two reactions and their equilibrium constants:

$$2NOBr(g) \rightleftharpoons 2NO(g) + Br_2$(g),\ K_1$ = 0.014$$

$$Br_2(g$$) + $$Cl_2(g$$) \rightleftharpoons 2BrCl(g),\ $$K_2 = 7.2$

What is the equilibrium constant for the reaction:

2$$NOBr(g) + $$Cl_2(g$$) \rightleftharpoons 2NO(g) + 2BrCl(g)$$?

Accepted Answer

$$K = 0.014 	imes 7.2$$

Question 5

For the reaction $$CaCO_3(s$$) \rightleftharpoons CaO(s) + $$CO_2(g$$)$$, which of the following is the correct expression for the equilibrium constant K$?

Accepted Answer

$$K = [CO_2$]$$

Question 6

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 7

If the equilibrium constant for $$A(g) \rightleftharpoons B(g) is$$ $$K_1$$, what is the equilibrium constant for $$2A(g) \rightleftharpoons 2B(g)$$?

Accepted Answer

$$K_1^2$

Question 8

Consider the following reaction at equilibrium:

$$3Fe(s) + 4H_2O(g) \rightleftharpoons Fe_3O_4(s) + 4H_2(g)$$

Which of the following would NOT affect the value of the equilibrium constant $$K$$?

Accepted Answer

Adding more $$Fe(s).$$

Question 9

Given the following reactions:

$$N_2(g) + 3H_2(g$$) \rightleftharpoons 2NH_3(g),\ $$K_1$$

$$2NH_3(g) \rightleftharpoons N_2$(g) + 3H_2(g),\ K_2$

What is the relationship between K_1$ and K_2$?

Accepted Answer

$$K_2 = 1$$/$$K_1$$

Question 10

A chemist combines the following two reactions:

$$A(g) \rightleftharpoons B(g),\ K_1$

B(g$$) \rightleftharpoons C(g),\ $$K_2$$

What is the equilibrium constant for the overall reaction $$A(g) \rightleftharpoons C(g)$$?

Accepted Answer

$$K_1$$ 	imes $$K_2$$

Question 11

For the reaction $$2NO_2(g) \rightleftharpoons N_2O_4(g)$$, the equilibrium constant is $$K = \frac{[N_2O_4]}{[NO_2$]^2}. If $$the reaction is written as $$N_2O_4(g) \rightleftharpoons 2NO_2(g)$$, what is the new equilibrium constant?

Accepted Answer

$$1/K$$

Question 12

Which of the following is NOT included in the equilibrium constant expression for the reaction $$CaCO_3(s$$) \rightleftharpoons CaO(s) + $$CO_2(g$$)$$?

Accepted Answer

$$[$$CaCO_3$$]$$

Question 13

A reaction has $$K = 1.0 	imes 10^3$ at a certain temperature. Which statement best describes the composition of the equilibrium mixture?

Accepted Answer

The mixture contains mostly products.

Question 14

For the reaction $$2NOBr(g) \rightleftharpoons 2NO(g) + Br_2$(g)$$, the equilibrium constant is $$K = \frac{[NO]^2[Br_2$]}{[NOBr]^2}. If $$the initial concentration of $$NOBr is $$increased, what happens to the value of $$K$$?

Accepted Answer

It remains the same.

Question 15

Which of the following best describes the law of mass action for a heterogeneous equilibrium involving $$CaCO_3(s$$) \rightleftharpoons CaO(s) + $$CO_2(g$$)$$?

Accepted Answer

$$K = [CO_2$]$$

Question 16

A reaction mixture at equilibrium contains $$[A] = 0.2\ \mathrm{M}$$, $$[B] = 0.5\ \mathrm{M}$$, and $$[C] = 0.1\ \mathrm{M}$$ for the reaction $$A(g) + 2B(g) \rightleftharpoons 3C(g). $$What is the value of the equilibrium constant $$K$$?

Accepted Answer

$$K = \frac{[C]^3}{[A][B]^2} = \frac{(0.1)^3$}{0.2 	imes (0.5)^2$}$$

Question 17

Which of the following changes will NOT affect the position of equilibrium for the reaction $$CaCO_3(s$$) \rightleftharpoons CaO(s) + $$CO_2(g$$)$$?

Accepted Answer

Adding more $$CaCO_3(s$$)$$.

Question 18

For the reaction $$2NO_2(g) \rightleftharpoons N_2O_4(g)$$, if the equilibrium constant is $$K = 4.0 at a $$certain temperature, what is the value of $$K$$ for the reaction $$N_2O_4(g) \rightleftharpoons 2NO_2(g)$$?

Accepted Answer

$$K = 0.25$$

Equilibrium Constants and Heterogeneous Equilibria

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