Q: For the reaction $$2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g)$$, what is the correct equilibrium expression?

$$K_c = \frac{[\text{SO}_3]^2}{[\text{SO}_2]^2[\text{O}_2]}$$

Q: If a reaction is reversed, how is the new equilibrium constant ($$K_{\text{new}}) $$related to the original ($$K_{\text{old}}$$)?

$$K_{\text{new}} = \frac{1}{K_{\text{old}}}$$

Q: If a reaction is multiplied by 2, how is the new equilibrium constant ($$K_{\text{new}}) $$related to the original ($$K_{\text{old}}$$)?

$$K_{\text{new}} = K_{\text{old}}^2$$

Question 1

Which statement best describes chemical equilibrium in a closed system?

Accepted Answer

At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction.

Question 2

For the reaction $$2	ext{SO}_2(g) + 	ext{O}_2(g) ightleftharpoons 2	ext{SO}_3(g)$$, what is the correct equilibrium expression?

Accepted Answer

$$K_c = \frac{[	ext{SO}_3]^2}{[	ext{SO}_2]^2[	ext{O}_2]}$$

Question 3

If the equilibrium constant $$K$$ for a reaction is very large, what does this indicate about the equilibrium mixture?

Accepted Answer

The mixture contains mostly products.

Question 4

For the reaction $$	ext{CaCO}_3(s) ightleftharpoons 	ext{CaO}(s) + 	ext{CO}_2(g)$$, what is the equilibrium expression?

Accepted Answer

$$K = P$$_{	ext{CO}$$_2}$$

Question 5

Which of the following does NOT appear in the equilibrium expression for a heterogeneous equilibrium?

Accepted Answer

Concentration of pure solids

Question 6

For the reaction $$	ext{N}_2(g) + 3	ext{H}_2(g) ightleftharpoons 2	ext{NH}_3(g)$$, the equilibrium constant in terms of pressure ($$K_p) $$and concentration ($$K_c) $$are related by $$K_p = K_c(RT$$)^{\Delta n}$$. What is $$\Delta n$$ for this reaction?

Accepted Answer

$$\Delta n = -2$$

Question 7

If a reaction is reversed, how is the new equilibrium constant ($$K_{	ext{new}}) $$related to the original ($$K_{	ext{old}}$$)?

Accepted Answer

$$K_{	ext{new}} = \frac{1}{K_{	ext{old}}}$$

Question 8

A mixture of H$$_2$$, I$$_2$$, and HI each at 55 atm is introduced into a container at 783 K. If $$K = 46$$ for $$	ext{H}_2(g) + 	ext{I}_2(g) ightleftharpoons 2	ext{HI}(g)$$, what is the value of the reaction quotient $$Q$$?

Accepted Answer

$$Q = \frac{(55)^2$}{(55)(55)} = 1$$

Question 9

Given the reaction $$	ext{H}_2(g) + 	ext{I}_2(g) ightleftharpoons 2	ext{HI}(g)$$, starting with 1 atm each of H$$_2$$ and I$$_2$$, the equilibrium pressure of HI is 0.8 atm. What are the equilibrium pressures of H$$_2$$ and I$$_2$$?

Accepted Answer

0.6 atm each

Question 10

For the reaction $$	ext{H}_2(g) + 	ext{I}_2(g) ightleftharpoons 2	ext{HI}(g)$$, using the equilibrium pressures $$P_{	ext{HI}} = 0.8$$ atm, $$P_{	ext{H}_2$$} = 0.6$$ atm, P$$_{	ext{I}$$_2} = 0.6$$ atm, what is the equilibrium constant $$K$$?

Accepted Answer

$$K = \frac{(0.8)^2$}{(0.6)(0.6)} = 1.78$$

Question 11

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

Accepted Answer

The reaction favors reactants at equilibrium.

Question 12

For the reaction $$	ext{PCl}_5(g) ightleftharpoons 	ext{PCl}_3(g) + 	ext{Cl}_2(g)$$, if $$K = 33 at 250$$°C and the initial concentrations are $$[	ext{PCl}_3] = 0.050 M $$and $$[	ext{Cl}_2] = 0.015 M$$, what is the equilibrium concentration of $$	ext{PCl}_5$$?

Accepted Answer

0.00876 M

Question 13

Which of the following best describes the effect of increasing the concentration of products in a reversible reaction at equilibrium?

Accepted Answer

The reaction shifts toward the reactants.

Question 14

If a reaction is multiplied by 2, how is the new equilibrium constant ($$K_{	ext{new}}) $$related to the original ($$K_{	ext{old}}$$)?

Accepted Answer

$$K_{	ext{new}} = K_{	ext{old}}^2$$

Question 15

A reaction mixture has $$Q \u003c K. $$What will happen as the system moves toward equilibrium?

Accepted Answer

The concentration of products will increase.

Question 16

For the reaction $$	ext{CO}_2(g) + 	ext{C}(s) ightleftharpoons 2	ext{CO}(g)$$, what is the equilibrium expression?

Accepted Answer

$$K = \frac{[	ext{CO}]^2}{[	ext{CO}_2]}$$

Question 17

Which of the following is true about the equilibrium constant $$K$$?

Accepted Answer

It is constant at a given temperature.

Question 18

In a reaction vessel, 1.0 mol of N$$_2O$_4 is $$placed in a 1.0-L container and allowed to reach equilibrium: $$	ext{N}_2	ext{O}_4(g) ightleftharpoons 2	ext{NO}_2(g). If at $$equilibrium, N$$_2O$_4 is 28$$% dissociated, what is the equilibrium concentration of NO$$_2$$?

Accepted Answer

0.56 M

Chemical Equilibrium: Principles, Expressions, and Calculations

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