Question 1

Which statement best describes chemical equilibrium in a closed system?

Accepted Answer

The rates of the forward and reverse reactions are equal.

Question 2

For the reaction $$\mathrm{N_2O_4(g) \rightleftharpoons 2 NO_2$(g)}$$, the equilibrium constant expression is:

Accepted Answer

$$\displaystyle K_c = \frac{[NO_2$]^2}{[N_2O_4]}$$

Question 3

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

Accepted Answer

Products predominate.

Question 4

For the reaction $$\mathrm{aA + bB \rightleftharpoons cC + dD}$$, the general equilibrium constant expression is:

Accepted Answer

$$\displaystyle K_c = \frac{[C]^c [D]^d}{[A]^a [B]^b}$$

Question 5

Which of the following would NOT appear in the equilibrium constant expression for the reaction $$\mathrm{$$PbCl_2$$(s) \rightleftharpoons Pb$$^{2+}$$(aq) + 2 Cl^-(aq)}$$?

Accepted Answer

$$[$$PbCl_2$$]$$

Question 6

For the reaction $$\mathrm{N_2$(g) + O_2$(g) \rightleftharpoons 2 NO(g)}$$ with initial concentrations $$[N_2$] = 0.200\,M$$, $$[O_2$] = 0.200\,M$$, and $$[NO] = 0.00\,M$$, if $$K_c = 0.10$$, which equation would you use to solve for the equilibrium concentration of $$NO$$?

Accepted Answer

$$\displaystyle K_c = \frac{[NO]^2}{[N_2$][O_2$]}$$

Question 7

A catalyst is added to a reaction mixture at equilibrium. What is the effect on the equilibrium composition?

Accepted Answer

The equilibrium composition remains unchanged.

Question 8

For the reaction $$\mathrm{CO_2$(g) + H_2$(g) \rightleftharpoons CO(g) + H_2O(g)}$$, if $$H_2 is $$added to the system, what happens to the amount of $$CO at $$equilibrium?

Accepted Answer

It increases.

Question 9

For the reaction $$\mathrm{CO_2$(g) + H_2$(g) \rightleftharpoons CO(g) + H_2O(g)}$$, if $$H_2O is $$added to the system, what happens to the amount of $$CO at $$equilibrium?

Accepted Answer

It decreases.

Question 10

For the reaction $$\mathrm{CO_2$(g) + H_2$(g) \rightleftharpoons CO(g) + H_2O(g)}$$, if the reaction is endothermic and the temperature is raised, what happens to the amount of $$CO at $$equilibrium?

Accepted Answer

It increases.

Question 11

For the reaction $$\mathrm{CO_2$(g) + H_2$(g) \rightleftharpoons CO(g) + H_2O(g)}$$, if the container is compressed (volume decreased), what happens to the amount of $$CO at $$equilibrium?

Accepted Answer

It decreases.

Question 12

For the reaction $$\mathrm{2 H_2S(g) ightleftharpoons 2 H_2$(g) + S_2$(g)}$$ with $$K_c = 1.67 	imes 10$$^{-7}$$ at 800$$^\circ$$C, and an initial concentration $$[H_2S] = 0.0250\,M$$, which approximation is valid for solving equilibrium concentrations?

Accepted Answer

Assume $$[H_2S]$$ remains nearly constant.

Question 13

For the reaction $$\mathrm{P_4$(s) + 6 Cl_2$(g) \rightleftharpoons 4 $$PCl_3$$(l)}$$, which is the correct equilibrium constant expression?

Accepted Answer

$$\displaystyle K_c = \frac{1}{[Cl_2$]^6}$$

Question 14

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

Accepted Answer

The reaction will shift to form more products.

Question 15

In the Haber process for ammonia synthesis, what is the effect of removing ammonia ($$NH_3) $$from the system as it forms?

Accepted Answer

The equilibrium shifts to produce more $$NH_3.$$

Question 16

For a reaction where $$K_p$$ and $$K_c$$ are related by $$K_p = K_c (RT$$)^{\Delta n}$$, what does $$\Delta n$$ represent?

Accepted Answer

The difference in moles of gaseous products and reactants.

Question 17

Which of the following best describes the effect of a catalyst on a reaction at equilibrium?

Accepted Answer

It increases the rate of both forward and reverse reactions.

Question 18

A system at equilibrium is disturbed by increasing the concentration of a reactant. According to Le Châtelier’s Principle, what happens?

Accepted Answer

The equilibrium shifts to produce more products.

Chemical Equilibrium: Concepts, Calculations, and Applications

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