Q: For the reaction $$\mathrm{N_2O_4 (g) \rightleftharpoons 2 NO_2$ (g)}$$, $$K_c = 4.63 \times 10$$^{-3}$$ at 25$$^\circ$$C. What is K_p$ at this temperature? (R = 0.0821$$\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot $$K^{-1}$$}$$, T = 298$$\ \mathrm{K}$$)

$$K_p = K_c(RT$$)^{\Delta n}$$ = (4.63 \times 10$$^{-3}$$)(0.0821 \times 298)^1$ = 0.113$$

Question 1

Which statement best describes the concept of dynamic equilibrium as illustrated by the decomposition of $$\mathrm{N_2O_4} to$$ $$\mathrm{NO_2$} in $$the provided diagram?

Accepted Answer

At equilibrium, the rates of the forward and reverse reactions are equal, so the concentrations of $$\mathrm{N_2O_4}$$ and $$\mathrm{NO_2$}$$ remain constant.

Question 2

Given the reaction $$\mathrm{N_2O_4 (g) \rightleftharpoons 2 NO_2$ (g)}$$, which of the following is the correct equilibrium expression for $$K_c$$?

Accepted Answer

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

Question 3

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

Accepted Answer

Products are favored at equilibrium.

Question 4

For the reaction $$\mathrm{CO_2$ (g) + C (s) \rightleftharpoons 2 CO (g)}$$, which species are included in the equilibrium expression?

Accepted Answer

Only $$\mathrm{CO_2$}$$ and $$\mathrm{CO}$$

Question 5

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

Accepted Answer

$$\frac{1}{K_c}$$

Question 6

Given the reaction $$\mathrm{N_2$ (g) + 3 H_2$ (g) \rightleftharpoons 2 NH_3$ (g)}$$ with $$K_c = 1.2 at$$ $$375^\circC$$, if $$[\mathrm{N_2$}] = 1.0\ \mathrm{M}$$, $$[\mathrm{H_2$}] = 0.57\ \mathrm{M}$$, and $$[\mathrm{NH_3$}] = 1.3\ \mathrm{M}$$, what is the value of $$Q_c$$?

Accepted Answer

$$Q_c = \frac{[\mathrm{NH_3$}]^2}{[\mathrm{N_2$}][\mathrm{H_2$}]^3} = \frac{(1.3)^2$}{(1.0)(0.57)^3$} = 13.9$$

Question 7

Which change will shift the equilibrium to the right for the exothermic reaction $$\mathrm{2 SO_2$ (g) + O_2$ (g) \rightleftharpoons 2 SO_3$ (g)}$$?

Accepted Answer

Decreasing the temperature

Question 8

For the reaction $$\mathrm{N_2O_4 (g) ightleftharpoons 2 NO_2$ (g)}$$, $$K_c = 4.63 	imes 10$$^{-3}$$ at 25$$^\circ$$C. What is K_p$ at this temperature? (R = 0.0821$$\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot $$K^{-1}$$}$$, T = 298$$\ \mathrm{K}$$)

Accepted Answer

$$K_p = K_c(RT$$)^{\Delta n}$$ = (4.63 	imes 10$$^{-3}$$)(0.0821 	imes 298)^1$ = 0.113$$

Question 9

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

Accepted Answer

Adding a catalyst

Question 10

For the reaction $$\mathrm{2 NOCl (g) ightleftharpoons 2 NO (g) + Cl_2$ (g)}$$ with $$K_c = 1.6 	imes 10$$^{-5}$$, if the initial concentration of $$\mathrm{NOCl}$$ is 2.3$$\ \mathrm{M}$$ and no products are present, what is the correct setup for the equilibrium concentrations using x$?

Accepted Answer

$$[\mathrm{NOCl}] = 2.3 - 2x$$, $$[\mathrm{NO}] = 2x$$, $$[\mathrm{Cl_2$}] = x$$

Question 11

Which of the following best describes the effect of increasing pressure on the equilibrium of $$\mathrm{N_2$ (g) + 3 H_2$ (g) \rightleftharpoons 2 NH_3$ (g)}$$?

Accepted Answer

The equilibrium shifts to the side with fewer gas molecules.

Question 12

If $$Q_c \u003c K_c$$ for a reaction mixture, what will happen as the system moves toward equilibrium?

Accepted Answer

Reactants will be converted to products.

Question 13

Which of the following is true for a heterogeneous equilibrium involving solids and gases?

Accepted Answer

Only the concentrations of gases are included in the equilibrium expression.

Question 14

For the reaction $$\mathrm{A_2$ (g) + B_2$ (g) \rightleftharpoons 2 AB (g)}$$, if the equilibrium constant for the forward reaction is $$K_c$$, what is the equilibrium constant for $$\mathrm{4 AB (g) \rightleftharpoons 2 A_2$ (g) + 2 B_2$ (g)}$$?

Accepted Answer

$$\frac{1}{K_c^2$}$$

Question 15

A reaction mixture at equilibrium is disturbed by adding more product. According to Le Châtelier’s principle, what will happen?

Accepted Answer

The equilibrium will shift to produce more reactant.

Question 16

Which of the following is the correct relationship between $$K_p$$ and $$K_c$$ for the reaction $$aA (g) \rightleftharpoons bB (g)$$?

Accepted Answer

$$K_p = K_c(RT$$)^{\Delta n}$$

Chemical Equilibrium: Principles, Calculations, and Applications

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