Q: Given the following reactions and their equilibrium constants: $$\mathrm{A \rightleftharpoons B}$$, $$K_1 = 2.0$ $$\mathrm{B \rightleftharpoons C}$$, K_2$ = 3.0$$ What is the equilibrium constant $$K$$ for the reaction $$\mathrm{A \rightleftharpoons C}$$?

$$K = K_1$ \times K_2$ = 2.0 \times 3.0 = 6.0$$

Q: For the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)}$$, $$K_c = 4.0 at a $$certain temperature. If the total number of moles of gas decreases during the reaction, which of the following correctly relates $$K_p$$ and $$K_c$$?

$$K_p = K_c(RT$$)^{\Delta n}$$, where $$\Delta n = \text{moles of gaseous products} - \text{moles of gaseous reactants}$$

Q: If the equilibrium concentration of $$\mathrm{NO_2$} in $$the reaction $$\mathrm{2NO_2(g) \rightleftharpoons N_2O_4(g)} is$$ $$0.20\ \mathrm{M}$$ and $$K_c = 5.0 at a $$certain temperature, what is the equilibrium concentration of $$\mathrm{N_2O_4} if$$ $$[\mathrm{NO_2$}] is $$the only reactant initially present at $$0.50\ \mathrm{M}$$?

$$[\mathrm{N_2O_4}] = K_c \times [\mathrm{NO_2$}]^2 = 5.0 \times (0.20)^2$ = 0.20\ \mathrm{M}$$

Question 1

Which of the following best describes a dynamic equilibrium in a chemical reaction?

Accepted Answer

The forward and reverse reactions occur at the same rate, so the concentrations of reactants and products remain constant over time.

Question 2

For the reaction $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$, the equilibrium constant $$K_c is$$ $$0.50 at a $$certain temperature. If the equilibrium concentrations are $$[\mathrm{N_2$}] = 0.20\ \mathrm{M}$$, $$[\mathrm{H_2$}] = 0.30\ \mathrm{M}$$, and $$[\mathrm{NH_3$}] = 0.40\ \mathrm{M}$$, what is the value of the reaction quotient $$Q_c$$?

Accepted Answer

$$Q_c = \dfrac{[\mathrm{NH_3$}]^2}{[\mathrm{N_2$}][\mathrm{H_2$}]^3} = \dfrac{(0.40)^2$}{(0.20)(0.30)^3$} = 29.6$$

Question 3

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

Accepted Answer

The reaction mixture contains mostly products at equilibrium.

Question 4

Given the following reactions and their equilibrium constants:

$$\mathrm{A \rightleftharpoons B}$$, $$K_1 = 2.0$

$$\mathrm{B \rightleftharpoons C}$$, K_2$ = 3.0$$

What is the equilibrium constant $$K$$ for the reaction $$\mathrm{A \rightleftharpoons C}$$?

Accepted Answer

$$K = K_1$ 	imes K_2$ = 2.0 	imes 3.0 = 6.0$$

Question 5

For the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)}$$, $$K_c = 4.0 at a $$certain temperature. If the total number of moles of gas decreases during the reaction, which of the following correctly relates $$K_p$$ and $$K_c$$?

Accepted Answer

$$K_p = K_c(RT$$)^{\Delta n}$$, where $$\Delta n = 	ext{moles of gaseous products} - 	ext{moles of gaseous reactants}$$

Question 6

A reaction mixture has $$Q_c = 0.10$$ and $$K_c = 1.0. $$Which statement is correct about the direction the reaction will proceed to reach equilibrium?

Accepted Answer

The reaction will proceed in the forward direction to form more products.

Question 7

If the equilibrium concentration of $$\mathrm{NO_2$} in $$the reaction $$\mathrm{2NO_2(g) \rightleftharpoons N_2O_4(g)} is$$ $$0.20\ \mathrm{M}$$ and $$K_c = 5.0 at a $$certain temperature, what is the equilibrium concentration of $$\mathrm{N_2O_4} if$$ $$[\mathrm{NO_2$}] is $$the only reactant initially present at $$0.50\ \mathrm{M}$$?

Accepted Answer

$$[\mathrm{N_2O_4}] = K_c 	imes [\mathrm{NO_2$}]^2 = 5.0 	imes (0.20)^2$ = 0.20\ \mathrm{M}$$

Question 8

Which of the following changes will shift the equilibrium of the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)} to $$the right, according to Le Chatelier’s Principle?

Accepted Answer

Removing $$\mathrm{SO_3$}$$ gas.

Question 9

Which of the following is a Bronsted-Lowry acid?

Accepted Answer

$$\mathrm{HCl}$$

Question 10

Which of the following is a strong acid?

Accepted Answer

$$\mathrm{$$HNO_3$$}$$

Question 11

Which proton is most likely to be donated by acetic acid ($$\mathrm{CH_3COOH}) $$when it reacts with a base?

Accepted Answer

The hydrogen attached to the oxygen in the carboxyl group ($$\mathrm{COOH})$$

Question 12

Given the following $$K_a$$ values for three acids:

Acid A: $$K_a = 1.0 	imes 10$$^{-5}$$

Acid B: K_a = 2.0$$ 	imes $$10^{-7}$$

Acid C: $$K_a = 5.0 	imes 10$$^{-4}$$

Rank the acids from strongest to weakest.

Accepted Answer

C \u003e A \u003e B

Question 13

What is the correct $$K_a$$ expression for the weak acid $$\mathrm{HA} in $$water?

Accepted Answer

$$K_a = \dfrac{[\mathrm{H_3O^+}][\mathrm{A^-}]}{[\mathrm{HA}]}$$

Question 14

What is the conjugate base of $$\mathrm{$$HCO_3$$^-}$$?

Accepted Answer

$$\mathrm{CO_3$^{2-}}$$

Question 15

Which of the following reactions represents the reaction of ammonia ($$\mathrm{NH_3$}) $$with water as a Bronsted-Lowry acid-base reaction?

Accepted Answer

$$\mathrm{NH_3$ + H_2O \rightarrow NH_4$^+ + OH^-}$$

Question 16

A solution has a pH of 3.5. Which statement is correct?

Accepted Answer

The solution is acidic.

Question 17

If $$K_w = 1.0 	imes 10$$^{-14}$$ at 25$$^\circ$$C, what is the $$[\mathrm{OH^-}]$$ in a solution with $$[\mathrm{H_3O^+}] = 1.0 	imes $$10^{-5}$$\ \mathrm{M}$$?

Accepted Answer

$$[\mathrm{OH^-}] = \dfrac{K_w}{[\mathrm{H_3O^+}]} = \dfrac{1.0 	imes 10$$^{-14}$$}{1.0 	imes 10$$^{-5}$$} = 1.0 	imes 10$$^{-9}$$\ \mathrm{M}$$

Question 18

A $$0.10\ \mathrm{M}$$ solution of a weak acid $$\mathrm{HA}$$ has a pH of $$3.0. $$What is the $$K_a of $$the acid?

Accepted Answer

$$K_a = \dfrac{[\mathrm{H_3O^+}]^2}{[\mathrm{HA}] - [\mathrm{H_3O^+}]} = \dfrac{(1.0 	imes 10$$^{-3}$$)^2$$}{0.10 - 1.0 	imes $$10^{-3}$$} \approx 1.0 	imes $$10^{-5}$

Chemical Equilibrium and Acids & Bases: Study Notes for General Chemistry

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