Question 1

For the reaction $$2\ \mathrm{SO_2$}(g) + \mathrm{O_2$}(g) \rightleftharpoons 2\ \mathrm{SO_3$}(g) at 1000 K$$, a 5.0 L vessel is filled with 1.00 mol SO$$_2$$ and 1.00 mol O$$_2. At $$equilibrium, 0.85 mol SO$$_3 is $$present. What is the value of $$K_c$$ for this reaction at 1000 K?

Accepted Answer

$$K_c = 0.289$$

Question 2

Given the reaction $$2\ \mathrm{IBr}(g) \rightleftharpoons \mathrm{I_2$}(g) + \mathrm{Br_2$}(g) at 500 K$$, 7.24 g of IBr is placed in a 225 mL container. At equilibrium, the partial pressure of Br$$_2 is 3.01 $$atm. What is the value of $$K_p$$ for this reaction at 500 K?

Accepted Answer

$$K_p = 6.02$$

Question 3

For the heterogeneous reaction $$\mathrm{CO_2$}(g) + \mathrm{C}(s) \rightleftharpoons 2\ \mathrm{CO}(g) at 1000 K$$, a vessel initially contains 0.464 atm of CO$$_2$$ and excess solid C. At equilibrium, the total vapor pressure is 0.746 atm. What is the equilibrium partial pressure of CO(g)?

Accepted Answer

$$P_{\mathrm{CO}} = 0.282\ \mathrm{atm}$$

Question 4

For the reaction $$2\ \mathrm{NOCl}(g) ightleftharpoons 2\ \mathrm{NO}(g) + \mathrm{Cl_2$}(g) at 35$$°C, $$K_c = 1.6 	imes 10$$^{-5}$$. If the initial concentration of NOCl is 0.500 mol/L, which statement best describes the equilibrium position?

Accepted Answer

The reaction hardly proceeds; most NOCl remains at equilibrium.

Question 5

For the reaction $$2\ \mathrm{SO_2$}(g) + \mathrm{O_2$}(g) ightleftharpoons 2\ \mathrm{SO_3$}(g) at 700 K$$, $$K_p = 8.24 	imes 10^4$. If the initial partial pressures are 0.490 atm SO_2$ and 0.245 atm O_2$, what can you conclude about the equilibrium mixture?

Accepted Answer

Almost all SO$$_2$$ and O$$_2$$ are converted to SO$$_3 at $$equilibrium.

Question 6

Which of the following correctly expresses the relationship between $$K_p$$ and $$K_c$$ for a gaseous reaction?

Accepted Answer

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

Question 7

A 2.00 L vessel contains 100 mg of solid C and CO$$_2$$ gas at 0.464 atm. For the reaction $$\mathrm{CO_2$}(g) + \mathrm{C}(s) \rightleftharpoons 2\ \mathrm{CO}(g) at 1000 K$$, the total pressure at equilibrium is 0.746 atm. What is the mass of C(s) remaining at equilibrium?

Accepted Answer

Less than 100 mg; some C(s) is consumed.

Question 8

If the equilibrium constant $$K_c$$ for a reaction is very small (e.g., $$K_c = 1.6 	imes 10$$^{-5}$$), what does this indicate about the position of equilibrium?

Accepted Answer

The reaction mixture contains mostly reactants at equilibrium.

Question 9

For the reaction $$2\ \mathrm{IBr}(g) \rightleftharpoons \mathrm{I_2$}(g) + \mathrm{Br_2$}(g)$$, if the partial pressure of Br$$_2 at $$equilibrium is 3.01 atm, what is the partial pressure of I$$_2 at $$equilibrium?

Accepted Answer

$$3.01\ \mathrm{atm}$$

Question 10

A reaction has $$\Delta n = 0. $$How does this affect the relationship between $$K_p$$ and $$K_c$$?

Accepted Answer

$$K_p = K_c$$

Question 11

For the reaction $$2\ \mathrm{NOCl}(g) \rightleftharpoons 2\ \mathrm{NO}(g) + \mathrm{Cl_2$}(g)$$, which of the following would increase the amount of NO at equilibrium?

Accepted Answer

Increasing the volume of the container

Question 12

Which of the following best describes why solids are omitted from equilibrium constant expressions?

Accepted Answer

Their concentrations do not change during the reaction.

Question 13

A reaction mixture at equilibrium is disturbed by adding more reactant. According to Le Chatelier's Principle, what will happen?

Accepted Answer

The system will shift to produce more products.

Question 14

For the reaction $$2\ \mathrm{SO_2$}(g) + \mathrm{O_2$}(g) \rightleftharpoons 2\ \mathrm{SO_3$}(g)$$, what is the effect of increasing the pressure by decreasing the volume of the container?

Accepted Answer

The equilibrium shifts toward SO$$_3$$ formation.

Question 15

If the temperature is increased for an exothermic reaction at equilibrium, what happens to the value of the equilibrium constant?

Accepted Answer

It decreases.

Question 16

For the reaction $$2\ \mathrm{NOCl}(g) ightleftharpoons 2\ \mathrm{NO}(g) + \mathrm{Cl_2$}(g)$$, if the initial concentration of NOCl is 0.500 mol/L and $$K_c = 1.6 	imes 10$$^{-5}$$, which approximation is valid for calculating equilibrium concentrations?

Accepted Answer

Assume the change in NOCl is negligible compared to its initial concentration.

Question 17

Which of the following is true for a reaction with a very large equilibrium constant ($$K \gg 1$$)?

Accepted Answer

The reaction mixture at equilibrium contains mostly products.

Question 18

For the reaction $$2\ \mathrm{SO_2$}(g) + \mathrm{O_2$}(g) ightleftharpoons 2\ \mathrm{SO_3$}(g)$$, if the initial partial pressures are 0.490 atm SO$$_2$$ and 0.245 atm O$$_2$$, and $$K_p = 8.24 	imes 10^4$, what is the approximate equilibrium partial pressure of SO_3$?

Accepted Answer

$$0.490\ \mathrm{atm} ($$almost all SO$$_2$$ converted)

Question 19

Which of the following is the correct equilibrium constant expression for the reaction $$2\ \mathrm{NOCl}(g) \rightleftharpoons 2\ \mathrm{NO}(g) + \mathrm{Cl_2$}(g)$$?

Accepted Answer

$$K_c = \dfrac{[\mathrm{NO}]^2 [\mathrm{Cl_2$}]}{[\mathrm{NOCl}]^2}$$

Chemical Equilibrium: Calculating Kc, Kp, and Equilibrium Concentrations/Pressures

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