Q: For the reaction $$2\text{NO}_2(g) \rightleftharpoons 2\text{NO}(g) + \text{O}_2(g)$$, which is the correct expression for the equilibrium constant $$K$$?

$$K = \dfrac{[\text{NO}]^2[\text{O}_2]}{[\text{NO}_2]^2}$$

Q: Consider the reaction $$\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$$ with $$K = 5.6 \times 10^5$. What is the equilibrium constant for the reverse reaction?

$$K_{\text{reverse}} = \dfrac{1}{5.6 \times 10^5$}$$

Q: Which of the following changes will NOT affect the position of equilibrium for the reaction $$\text{CaCO}_3(s) \rightleftharpoons \text{CaO}(s) + \text{CO}_2(g)$$?

Adding more $$\text{CaCO}_3(s)$$

Q: For the reaction $$\text{N}_2\text{O}_4(g) \rightleftharpoons 2\text{NO}_2(g)$$ with $$K_c = 0.36 at$$ $$100^\circC$$, if the initial concentration of $$\text{NO}_2 is$$ $$0.100\ \text{M}$$ and $$[\text{N}_2\text{O}_4] = 0$$, in which direction will the reaction proceed?

To the left, forming more $$\text{N}_2\text{O}_4$$

Q: For the reaction $$\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$$, $$K_c = 6.2 \times 10^2$ at 25$$^\circ$$C. What is the value of K_p$ at this temperature? (Assume R = 0.08206$$\ \text{L} \cdot \text{atm} / \text{mol} \cdot \text{K}$$ and T = 298$$\ \text{K}$$)

$$K_p = K_c \times (RT$$)^{\Delta n}$$, where $$\Delta n = 0$$; so K_p = K_c$

Question 1

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

Accepted Answer

The rates of the forward and reverse reactions are equal.

Question 2

For the reaction $$2	ext{NO}_2(g) ightleftharpoons 2	ext{NO}(g) + 	ext{O}_2(g)$$, which is the correct expression for the equilibrium constant $$K$$?

Accepted Answer

$$K = \dfrac{[	ext{NO}]^2[	ext{O}_2]}{[	ext{NO}_2]^2}$$

Question 3

A reaction mixture contains only products at the start. What is the value of the reaction quotient $$Q$$ and in which direction will the reaction proceed?

Accepted Answer

$$Q = \infty$$; reaction proceeds in reverse.

Question 4

Consider the reaction $$	ext{N}_2(g) + 3	ext{H}_2(g) ightleftharpoons 2	ext{NH}_3(g)$$ with $$K = 5.6 	imes 10^5$. What is the equilibrium constant for the reverse reaction?

Accepted Answer

$$K_{	ext{reverse}} = \dfrac{1}{5.6 	imes 10^5$}$$

Question 5

Which of the following changes will NOT affect the position of equilibrium for the reaction $$	ext{CaCO}_3(s) ightleftharpoons 	ext{CaO}(s) + 	ext{CO}_2(g)$$?

Accepted Answer

Adding more $$	ext{CaCO}_3(s)$$

Question 6

For the reaction $$2	ext{SO}_2(g) + 	ext{O}_2(g) ightleftharpoons 2	ext{SO}_3(g)$$, what is the effect of decreasing the volume of the reaction vessel?

Accepted Answer

The equilibrium shifts to the left, toward fewer moles of gas.

Question 7

Given the reaction $$	ext{CO}(g) + 2	ext{H}_2(g) ightleftharpoons 	ext{CH}_3	ext{OH}(g)$$, if the initial concentrations are $$[	ext{CO}] = 0.500\ 	ext{M}$$, $$[	ext{H}_2] = 1.00\ 	ext{M}$$, and $$[	ext{CH}_3	ext{OH}] = 0.00\ 	ext{M}$$, and at equilibrium $$[	ext{CO}] = 0.15\ 	ext{M}$$, what is the value of $$K_c$$?

Accepted Answer

$$K_c = 26$$

Question 8

Which statement about the effect of a catalyst on a chemical equilibrium is correct?

Accepted Answer

A catalyst speeds up both the forward and reverse reactions equally, but does not change the position of equilibrium.

Question 9

For the reaction $$	ext{N}_2	ext{O}_4(g) ightleftharpoons 2	ext{NO}_2(g)$$ with $$K_c = 0.36 at$$ $$100^\circC$$, if the initial concentration of $$	ext{NO}_2 is$$ $$0.100\ 	ext{M}$$ and $$[	ext{N}_2	ext{O}_4] = 0$$, in which direction will the reaction proceed?

Accepted Answer

To the left, forming more $$	ext{N}_2	ext{O}_4$$

Question 10

Which of the following best explains why the equilibrium constant $$K$$ has no units?

Accepted Answer

Because the units cancel due to the stoichiometry of the balanced equation.

Question 11

For the reaction $$	ext{H}_2(g) + 	ext{I}_2(g) ightleftharpoons 2	ext{HI}(g)$$, $$K_c = 6.2 	imes 10^2$ at 25$$^\circ$$C. What is the value of K_p$ at this temperature? (Assume R = 0.08206$$\ 	ext{L} \cdot 	ext{atm} / 	ext{mol} \cdot 	ext{K}$$ and T = 298$$\ 	ext{K}$$)

Accepted Answer

$$K_p = K_c 	imes (RT$$)^{\Delta n}$$, where $$\Delta n = 0$$; so K_p = K_c$

Question 12

Which of the following statements about Le Châtelier’s principle is correct?

Accepted Answer

Adding a reactant shifts the equilibrium toward the products.

Question 13

A reaction is exothermic. What is the effect of increasing the temperature on the equilibrium position and the value of $$K$$?

Accepted Answer

The equilibrium shifts left and $$K$$ decreases.

Question 14

Which of the following is the correct equilibrium constant expression for the reaction $$4	ext{HCl}(g) + 	ext{O}_2(g) ightleftharpoons 2	ext{H}_2	ext{O}(l) + 2	ext{Cl}_2(g)$$?

Accepted Answer

$$K_c = \dfrac{[	ext{Cl}_2]^2}{[	ext{HCl}]^4[	ext{O}_2]}$$

Question 15

If the equilibrium constant $$K$$ for a reaction is much less than 1, which of the following is true?

Accepted Answer

The reaction is reactant-favored at equilibrium.

Question 16

For the reaction $$2	ext{H}_2	ext{S}(g) ightleftharpoons 2	ext{H}_2(g) + 	ext{S}_2(g)$$ with $$K_c = 1.67 	imes 10$$^{-7}$$ at 800$$^\circ$$C, why is the 5% approximation valid when solving for equilibrium concentrations?

Accepted Answer

Because the change in concentration ($$x) is $$much smaller than the initial concentration.

Question 17

Which of the following best describes the effect of adding an inert gas at constant volume to a reaction at equilibrium?

Accepted Answer

It has no effect on the position of equilibrium.

Question 18

Fetal hemoglobin has a larger equilibrium constant for binding $$	ext{O}_2$$ than adult hemoglobin. What is the physiological significance of this difference?

Accepted Answer

Fetal hemoglobin binds $$	ext{O}_2$$ more efficiently, allowing $$	ext{O}_2 to be $$transferred from the mother to the fetus.

Chapter 15: Chemical Equilibrium – Structured Study Notes

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