Q: For the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)}$$, $$K_p = 0.33 at 1000 K. If$$ $$P_{SO_2$} = 0.16$$ atm, $$P_{O_2$} = 0.16$$ atm, and $$P_{SO_3$} = 0.25$$ atm, what is the value of $$Q_p$$?

$$Q_p = \dfrac{(0.25)^2$}{(0.16)^2$ \times 0.16} = 1.53$$

Q: A solution contains $$[CH_3COOH] = 1.65 \times 10$$^{-2}$$\ \mathrm{M}$$ and $$[CH_3COO^-] = [H^+] = 5.44 \times 10$$^{-4}$$\ \mathrm{M}. $$What is the equilibrium constant $$K$$ for the dissociation of acetic acid?

$$K = \dfrac{[CH_3COO^-][H^+]}{[CH_3COOH]} = \dfrac{(5.44 \times 10$$^{-4}$$)^2$$}{1.65 \times $$10^{-2}$$} = 1.79 \times $$10^{-5}$

Question 1

Which of the following best describes the difference between the equilibrium constant ($$K) $$and the reaction quotient ($$Q$$)?

Accepted Answer

$$K is $$calculated using equilibrium concentrations, while $$Q is $$calculated using concentrations at any point in the reaction.

Question 2

Given the reaction $$\mathrm{N_2$(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$$, if $$K_c = 0.50 at a $$certain temperature, what is the value of $$Q_c if$$ $$[N_2$] = 0.20\ \mathrm{M}$$, $$[H_2$] = 0.30\ \mathrm{M}$$, and $$[NH_3$] = 0.10\ \mathrm{M}$$?

Accepted Answer

$$Q_c = \dfrac{[NH_3$]^2}{[N_2$][H_2$]^3} = \dfrac{(0.10)^2$}{(0.20)(0.30)^3$} = 1.85$$

Question 3

If $$Q \u003e K$$ for a chemical reaction, what will happen to the system as it moves toward equilibrium?

Accepted Answer

The reaction will shift to the left, forming more reactants.

Question 4

For the reaction $$\mathrm{2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)}$$, $$K_p = 0.33 at 1000 K. If$$ $$P_{SO_2$} = 0.16$$ atm, $$P_{O_2$} = 0.16$$ atm, and $$P_{SO_3$} = 0.25$$ atm, what is the value of $$Q_p$$?

Accepted Answer

$$Q_p = \dfrac{(0.25)^2$}{(0.16)^2$ 	imes 0.16} = 1.53$$

Question 5

A solution contains $$[CH_3COOH] = 1.65 	imes 10$$^{-2}$$\ \mathrm{M}$$ and $$[CH_3COO^-] = [H^+] = 5.44 	imes 10$$^{-4}$$\ \mathrm{M}. $$What is the equilibrium constant $$K$$ for the dissociation of acetic acid?

Accepted Answer

$$K = \dfrac{[CH_3COO^-][H^+]}{[CH_3COOH]} = \dfrac{(5.44 	imes 10$$^{-4}$$)^2$$}{1.65 	imes $$10^{-2}$$} = 1.79 	imes $$10^{-5}$

Question 6

Which of the following statements about dynamic equilibrium is correct?

Accepted Answer

At dynamic equilibrium, the rates of the forward and reverse reactions are equal.

Question 7

A reaction mixture initially contains $$0.500 M$$ $$Br_2$$ and $$0.500 M$$ $$Cl_2. At $$equilibrium, $$[Br_2$] = 0.040 M$. What is the equilibrium concentration of $$BrCl$$ if the reaction is Br_2$(g) + Cl_2$(g) \rightleftharpoons 2BrCl(g)$?

Accepted Answer

$$[BrCl] = 0.46 M$$

Question 8

If the reaction quotient $$Q is $$less than the equilibrium constant $$K$$, what will happen to the concentrations of products and reactants as the system moves toward equilibrium?

Accepted Answer

The concentration of products will increase and the concentration of reactants will decrease.

Question 9

Which of the following is the correct equilibrium expression for the reaction $$aA + bB \rightleftharpoons cC + dD$$?

Accepted Answer

$$K = \dfrac{[C]^c[D]^d}{[A]^a[B]^b}$$

Question 10

A chemist wants to determine if a reaction is at equilibrium. She calculates $$Q$$ and finds $$Q = K. $$What does this indicate?

Accepted Answer

The reaction is at equilibrium.

Question 11

In a real-world scenario, why is it important for industrial chemists to monitor $$Q$$ and $$K$$ during large-scale chemical production?

Accepted Answer

To maximize product yield by adjusting conditions to favor the formation of products when $$Q \u003c K.$$

Question 12

A reaction has $$K = 2.5 	imes 10$$^{-3}$$. If the initial concentrations are $$[A] = 0.10$$ M, $$[B] = 0.10$$ M, and $$[C] = 0.10$$ M for the reaction A + B$$ ightleftharpoons C$$, what is Q$ and in which direction will the reaction proceed?

Accepted Answer

$$Q = \dfrac{[C]}{[A][B]} = \dfrac{0.10}{0.10 	imes 0.10} = 10$$; reaction shifts left.

Question 13

Which tool is most useful for systematically determining equilibrium concentrations when not all are known?

Accepted Answer

An ICE table

Question 14

For the reaction $$2NO_2(g) \rightleftharpoons N_2O_4(g)$$, if $$K_c = 4.0$$ and the initial concentrations are $$[NO_2$] = 0.60 M $$and $$[N_2O_4] = 0.20 M$$, what is the value of $$Q_c$$?

Accepted Answer

$$Q_c = \dfrac{[N_2O_4]}{[NO_2$]^2} = \dfrac{0.20}{(0.60)^2$} = 0.56$$

Equilibrium Constants, Reaction Quotients, and ICE Tables in Chemical Equilibrium

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