Q: If two reactions have equilibrium constants $$K_1$$ and $$K_2$$, and the overall reaction is the sum of the two, what is the equilibrium constant for the overall reaction?

$$K_{overall} = K_1$ \times K_2$

Question 1

For the reaction $$2\ \mathrm{SO}_2(g) + \mathrm{O}_2(g) \rightleftharpoons 2\ \mathrm{SO}_3(g)$$, which of the following is the correct equilibrium expression for $$K_c$$?

Accepted Answer

$$K_c = \frac{[\mathrm{SO}_3]^2}{[\mathrm{SO}_2]^2[\mathrm{O}_2]}$$

Question 2

A reaction mixture contains $$[\mathrm{H}_2] = 0.6\ \mathrm{atm}$$, $$[\mathrm{I}_2] = 0.6\ \mathrm{atm}$$, and $$[\mathrm{HI}] = 0.8\ \mathrm{atm} at $$equilibrium for the reaction $$\mathrm{H}_2(g) + \mathrm{I}_2(g) \rightleftharpoons 2\ \mathrm{HI}(g). $$What is the value of $$K$$?

Accepted Answer

$$K = \frac{(0.8)^2$}{(0.6)(0.6)} = 1.78$$

Question 3

For the reaction $$\mathrm{N}_2(g) + 3\ \mathrm{H}_2(g) \rightleftharpoons 2\ \mathrm{NH}_3(g)$$, if $$K_c = 0.50 at a $$certain temperature, what does this indicate about the composition of the equilibrium mixture?

Accepted Answer

The mixture contains mostly reactants.

Question 4

Which of the following statements about heterogeneous equilibrium is correct?

Accepted Answer

Only gases and aqueous species appear in the equilibrium expression.

Question 5

Given the reaction $$\mathrm{CaCO}_3(s) \rightleftharpoons \mathrm{CaO}(s) + \mathrm{CO}_2(g)$$, what is the correct equilibrium expression?

Accepted Answer

$$K = [\mathrm{CO}_2]$$

Question 6

For the reaction $$\mathrm{N}_2(g) + 3\ \mathrm{H}_2(g) \rightleftharpoons 2\ \mathrm{NH}_3(g)$$, the value of $$K_p is $$related to $$K_c by $$which equation?

Accepted Answer

$$K_p = K_c(RT$$)^{-2}$$

Question 7

If the equilibrium constant for a reaction is $$K$$, what is the equilibrium constant for the reverse reaction?

Accepted Answer

$$1/K$$

Question 8

A mixture of $$\mathrm{H}_2$$, $$\mathrm{I}_2$$, and $$\mathrm{HI}$$ each at $$55\ \mathrm{atm} is $$introduced into a container at $$783\ \mathrm{K}$$ for the reaction $$\mathrm{H}_2(g) + \mathrm{I}_2(g) \rightleftharpoons 2\ \mathrm{HI}(g)$$, where $$K = 46. $$What will happen to the concentration of HI?

Accepted Answer

HI will form from H2 and I2.

Question 9

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

Accepted Answer

The reaction will shift toward reactants.

Question 10

For the reaction $$\mathrm{PCl}_5(g) \rightleftharpoons \mathrm{PCl}_3(g) + \mathrm{Cl}_2(g)$$ with $$K = 33 at$$ $$250^\circ\mathrm{C}$$, if the initial concentrations are $$[\mathrm{PCl}_3] = 0.050\ \mathrm{M}$$ and $$[\mathrm{Cl}_2] = 0.015\ \mathrm{M}$$, what is the equilibrium concentration of $$\mathrm{PCl}_5$$?

Accepted Answer

$$0.0088\ \mathrm{M}$$

Question 11

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 12

If a reaction at equilibrium is multiplied by 2, how is the new equilibrium constant $$K_{new}$$ related to the original $$K_{old}$$?

Accepted Answer

$$K_{new} = K_{old}^2$$

Question 13

A 1.0 mol sample of $$\mathrm{N}_2O_4 is $$placed in a 1.0 L container and allowed to reach equilibrium: $$\mathrm{N}_2O_4(g) \rightleftharpoons 2\ \mathrm{NO}_2(g). If$$ $$28.0\% of$$ $$\mathrm{N}_2O_4 is $$dissociated at equilibrium, what is the value of $$K_c$$?

Accepted Answer

$$K_c = \frac{(0.56)^2$}{0.72} = 0.44$$

Question 14

Which of the following best describes the effect of increasing the concentration of a reactant in a system at equilibrium?

Accepted Answer

The reaction shifts to produce more products.

Question 15

For the reaction $$\mathrm{CO}_2(g) + \mathrm{C}(s) \rightleftharpoons 2\ \mathrm{CO}(g)$$, what is the correct equilibrium expression?

Accepted Answer

$$K = \frac{[\mathrm{CO}]^2}{[\mathrm{CO}_2]}$$

Question 16

A reaction has $$K = 1.0 	imes 10$$^{-5}$$. Which statement is true about the equilibrium mixture?

Accepted Answer

The mixture contains mostly reactants.

Question 17

If two reactions have equilibrium constants $$K_1$$ and $$K_2$$, and the overall reaction is the sum of the two, what is the equilibrium constant for the overall reaction?

Accepted Answer

$$K_{overall} = K_1$ 	imes K_2$

Question 18

Which of the following is true about the reaction quotient $$Q$$ and the equilibrium constant $$K$$?

Accepted Answer

If $$Q = K$$, the system is at equilibrium.

Chemical Equilibrium: Principles, Expressions, and Calculations

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