Q: A mixture contains $$[\mathrm{A}] = 0.20\ \mathrm{M}$$, $$[\mathrm{B}] = 0.30\ \mathrm{M}$$, and $$[\mathrm{C}] = 0.30\ \mathrm{M}$$ for the reaction $$\mathrm{A} + \mathrm{B} \rightleftharpoons \mathrm{C}. $$What is the value of $$K_c$$?

$$K_c = \dfrac{0.30}{0.20 \times 0.30}$$

Question 1

Which of the following best describes a chemical equilibrium in a closed system?

Accepted Answer

The rate of the forward reaction equals the rate of the reverse reaction, and the concentrations of reactants and products remain constant.

Question 2

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 constant expression $$K_c$$?

Accepted Answer

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

Question 3

If the equilibrium constant $$K_c$$ for a reaction is much greater than 1, what does this indicate about the position of equilibrium?

Accepted Answer

The reaction favors the formation of products.

Question 4

Consider the reaction $$\mathrm{N}_2(g) + 3\mathrm{H}_2(g) \rightleftharpoons 2\mathrm{NH}_3(g). If $$the volume of the reaction vessel is decreased at constant temperature, what will happen to the equilibrium position?

Accepted Answer

The equilibrium will shift toward the side with fewer moles of gas.

Question 5

For the reaction $$\mathrm{A}(g) + \mathrm{B}(g) \rightleftharpoons \mathrm{C}(g) + \mathrm{D}(g)$$, the equilibrium constant $$K_c is $$given by:

Accepted Answer

$$K_c = \dfrac{[\mathrm{C}][\mathrm{D}]}{[\mathrm{A}][\mathrm{B}]}$$

Question 6

A mixture contains $$[\mathrm{A}] = 0.20\ \mathrm{M}$$, $$[\mathrm{B}] = 0.30\ \mathrm{M}$$, and $$[\mathrm{C}] = 0.30\ \mathrm{M}$$ for the reaction $$\mathrm{A} + \mathrm{B} \rightleftharpoons \mathrm{C}. $$What is the value of $$K_c$$?

Accepted Answer

$$K_c = \dfrac{0.30}{0.20 	imes 0.30}$$

Question 7

Which of the following changes will NOT affect the position of equilibrium for a chemical reaction?

Accepted Answer

Adding a catalyst

Question 8

For the exothermic reaction $$2\mathrm{SO}_2(g) + \mathrm{O}_2(g) \rightleftharpoons 2\mathrm{SO}_3(g)$$, $$\Delta H = -198\ \mathrm{kJ}$$, what will happen to the equilibrium if the temperature is increased?

Accepted Answer

The equilibrium will shift toward the reactants.

Question 9

Given the reaction $$\mathrm{H}_2(g) + \mathrm{I}_2(g) \rightleftharpoons 2\mathrm{HI}(g)$$ with $$K_c = 49 at$$ $$450^\circ\mathrm{C}$$, if $$0.22$$ mol of $$\mathrm{H}_2$$, $$0.22$$ mol of $$\mathrm{I}_2$$, and $$0.66$$ mol of $$\mathrm{HI}$$ are placed in a $$1.00-L $$container, what is the value of $$Q$$ and in which direction will the reaction proceed?

Accepted Answer

$$Q = \dfrac{(0.66)^2$}{(0.22)(0.22)} = 9.0$$, reaction will proceed to the left.

Question 10

Which of the following statements about the reaction quotient $$Q is $$correct?

Accepted Answer

$$Q$$ uses initial or current concentrations and can be compared to $$K_c to $$predict the direction of the reaction.

Question 11

For the reaction $$\mathrm{CO}(g) + \mathrm{Cl}_2(g) \rightleftharpoons 2\mathrm{COCl}_2(g)$$, how does the equilibrium constant $$K_p$$ relate to $$K_c$$?

Accepted Answer

$$K_p = K_c(RT$$)^{\Delta n}$$, where $$\Delta n$$ is the change in moles of gas.

Question 12

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

Accepted Answer

Their concentrations are constant and do not affect the equilibrium.

Question 13

In the Haber process for ammonia synthesis, which condition would most favor the formation of ammonia ($$\mathrm{NH}_3$$)?

Accepted Answer

Low temperature and high pressure

Question 14

For the reaction $$\mathrm{N}_2(g) + 3\mathrm{H}_2(g) \rightleftharpoons 2\mathrm{NH}_3(g)$$, what is the effect of removing ammonia ($$\mathrm{NH}_3) $$from the reaction vessel as it forms?

Accepted Answer

The equilibrium shifts to the right, favoring more product formation.

Question 15

Which of the following is the correct relationship between standard free energy change $$\Delta G^\circ$$ and the equilibrium constant $$K$$?

Accepted Answer

$$\Delta G^\circ = -RT \ln K$$

Question 16

A catalyst is added to a system at equilibrium. What is the effect on the equilibrium concentrations of reactants and products?

Accepted Answer

Equilibrium concentrations remain unchanged; equilibrium is reached faster.

Question 17

For the reaction $$\mathrm{NO}_2(g) \rightleftharpoons \mathrm{N}_2\mathrm{O}_4(g)$$, what will happen to the equilibrium position if the pressure is increased by decreasing the volume?

Accepted Answer

The equilibrium will shift toward $$\mathrm{N}_2\mathrm{O}_4.$$

Question 18

If the reaction $$\mathrm{A}(g) + \mathrm{B}(g) \rightleftharpoons \mathrm{C}(g) is at $$equilibrium and the volume of the container is suddenly doubled, what will happen to the concentrations and the direction of the shift?

Accepted Answer

Concentrations decrease and the reaction shifts to the left.

Chemical Equilibrium: Principles, Expressions, and Calculations

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