AP Chemistry Unit 5 Test Review

AP Chemistry Unit 5 Test Review

Topics Covered:

Gaseous Equilibrium

Precipitation Equilibrium

Section I: Multiple Choice (50% of test grade) ~ 25-30 min to complete.

1. BaSO4 (s)  Ba+2 (aq) + SO4-2 (aq)

Consider the equilibrium system above. Which of the following statements are true?

(A) Adding a solution of 6 M NaSO4 will make the barium sulfate more soluble.
(B) Adding more barium sulfate will increase the value of the equilibrium constant.

(D) The equilibrium constant will always be less than 1 under standard conditions.

2. In which of the following systems would the equilibrium constant not be impacted by using molarity or partial pressures in the expression?

(A) CO(g) + NO(g) <===> CO2(g) + 1/2 N2(g)
(B) N2(g) + 3 H2(g) <===> 2 NH3(g)
(C) NO(g) + O3(g) <===> NO2(g) + O2(g)
(D) N2O4(g) <===> 2 NO2(g)

3. PCl3(g) + Cl2(g)  PCl5(g) H < 0

For the equilibrium reaction above, which of the following statements are NOT true when the system attempts to reestablish equilibrium?

(A) Increasing volume will cause a decrease in the concentration of Cl2.
(B) Decreasing the temperature will cause an increase in the concentration of PCl3.
(C) Increasing the temperature will cause the Keq value to increase.
(D) Decreasing pressure will cause a decrease in the concentration of Cl2.

4. For the reaction A(g)  B(g) + C(g), the equilibrium constant, Kp, is 2 x 10¯4 at 25 °C. A mixture of the three gases at 25 °C is placed in a reaction flask and the initial pressures are PA = 2 atm, PB = 0.5 atm, and PC = 1 atm, At the instant of mixing, which of the following is true for the reaction as written?

(A) G < 0
(B) G > 0
(C) G° < 0
(D) G° > 0

5. 2 SO2(g) + O2(g)  2 SO3(g)

When 0.40 mole of SO3 and 0.60 mole of O2 are placed in an evacuated 1.00-liter flask, the reaction represented above occurs. After the reactants and the product reach equilibrium and the initial temperature is restored, the flask is found to contain 0.30 mole of S03. Based on these results, the expression for the equilibrium constant, Kc, of the reaction is

(A) (0.30)2 / [(0.45)(0.10)2]

(B) (0 30)2 / [(0.60)(0.40)2]

(D) (0.30) / [(0.45)(0.10)]

6. 2NO(g) + O2(g) 2 NO2(g) H < 0

Which of the following changes alone would cause a decrease in the value of Keq for the reaction represented above?

A) Decreasing the temperature
B) Increasing the temperature
C) Decreasing the volume of the reaction vessel
D) Increasing the volume of the reaction vessel

7. The solubility of Bi2S3 is 1 x 10¯15 molar. What is the solubility product constant, Ksp, for Bi2S3?

(A) 1 x 10¯30
(B) 4 x 10¯45
(C) 1 x 10¯73
(D) 1 x 10¯75

8.MnS(s) + 2 H+ <===> Mn2+ + H2S(g)

MnS reacts with a strong acid as shown with the equation above. At 25 °C the solubility product constant, Ksp, for MnS is 5 x 10¯15 and the acid dissociation constants K1 and K2 for H2S are represented by the equations below:

H2S <===> HS- + H+ K1 = 1 x 10¯7

HS- <===> S-2 + H+ K2 = 1 x 10¯13

What is the equilibrium constant for the reaction represented by the equation above at 25 °C?

(A) 1 x 10¯13 / 5 x 10¯15
(B) 5 x 10¯15 / 1 x 10¯7
(C) 1 x 10¯7 / 5 x 10¯20
(D) 5 x 10¯15 / 1 x 10¯20

Questions 9-12: Consider an equilibrium system based on the reaction below. This equilibrium mixture is contained in a piston:

2SO2 (g) + O2(g) ⇌ 2SO3(g) + heat

9. Which occurs when the volume of the system is increased at constant temperature?

# molecules of SO2 / total # of molecules of all gases / Kp
a. / Increases / Decreases / Remains the same
b. / Increases / Remains the same / Remains the same
c. / Increases / Increases / Remains the same
d. / Remains the same / Decreases / Decreases

10. Which occurs when the force on the piston is decreased at constant temperature?

11. Which occurs when the temperature of the system is increased at constant volume?

# molecules of SO2 / total # of molecules of all gases / Kp
a. / Increases / Decreases / Remains the same
b. / Increases / Increases / Decreases
c. / Remains the same / Increases / Remains the same
d. / Remains the same / Decreases / Decreases

12. Which occurs when the oxygen is added to the system at constant volume and temperature?

# molecules of SO2 / total # of molecules of all gases / Kp
a. / Increases / Decreases / Remains the same
b. / Decreases / Increases / Remains the same
c. / Increases / Increases / Remains the same
d. / Remains the same / Decreases / Decreases

13. CH4 (g) + CO2 (g)  2CO (g) + 2H2 (g)

A 1.00 L flask is filled with 0.30 mol of CH4 and 0.40 mol of CO2, and allowed to come to equilibrium, as represented by the equation above. At equilbrium, there are 0.20 mol of CO in the flask. What is the value of the Kc for the reaction?

(A) 1.2

(B) 0.027

(D) 0.060

Questions 14 & 15:

2 CH4 (g)  C2H2 (g) + 3H2 (g)

The above reaction takes place in a sealed flask under standard conditions. The Kc for the reaction is equal to 0.016. At a point in the reaction the following concentration are determined in the table below:

[CH4] / [C2H2] / [H2]
1.0 / 0.50 / 2.0

14. Which of the following statements is true?

(A) The reaction will shift in the forward direction to reach equilibrium.

(B) The reaction will shift in the reverse direction to reach equilibrium.

(D) The reaction will go to completion because CH4 is decomposing.

15. Under standard conditions, the products in this reaction are

(A) Never favored

(B) Always favored

(D) Only favored when the pressure is decreased

Section II – Free Response (50% of test grade)

Free Response : Part A – (calculator maybe used for this section) ~ 45 min to complete

Your responses to these questions will be graded on the basis of the accuracy and relevance of the information cited. Explanations should be clear and well organized. Examples and equations may be included in your responses where appropriate. Specific answers are preferable to broad, diffuse responses.

1. CO2(g) + H2(g) H2O(g) + CO(g)

When H2(g) is mixed with CO2(g) at 2,000 K, equilibrium is achieved according to the equation above. In one experiment, the following equilibrium concentrations were measured.

[H2]= 0.20 mol/L

[CO2]= 0.30 mol/L

[H2O] = [CO] = 0.55 mol/L

(a)What is the mole fraction of CO(g) in the equilibrium mixture?

(b)Using the equilibrium concentrations given above, calculate the value of Kc, the equilibrium constant for the reaction.

(c)Determine Kp in terms of Kc for this system.

(d)When the system is cooled from 2,000 K to a lower temperature, 30.0 percent of the CO(g) is converted back to CO2(g). Calculate the value of Kc at this lower temperature.

2. Answer the questions relating to the solubility of silver chromate, Ag2CrO4

Silver chromate dissociates in water according to the following equation:

Ag2CrO4(s)  2 Ag+(aq) + CrO42–(aq) Ksp = 2.610–12 at 25˚C

(a)Write the equilibrium constant expression for the dissolving of Ag2CrO4.

(b)Calculate the concentration in mol L–1, of Ag+ in a saturated solution of Ag2CrO4 at 25˚C.

(c)Calculate the maximum mass in grams of Ag2CrO4 that can dissolve in 100. mL of water at 25˚C.

(d)A 0.100 mol sample of solid AgNO3 is added to 1.00 L saturated solution of Ag2CrO4. Assuming no volume change, does [CrO42–] increase, decrease, or remain the same? Justify your answer.

Equations Practice

For each of the following three reactions, in part (i) write a balanced equation for the reaction and in part (ii) answer the question about the reaction. In part (i), coefficients should be in terms of lowest whole numbers. Assume that solutions are aqueous unless otherwise indicated. Represent substances in solutions as ions if the substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction.

1. (a) Ammonia is added to a saturated solution of silver chloride.

(i) Balanced equation:

(ii) What is the cooridination # for the complex ion formed? Explain.

(b). Concentrated hydrochloric acid is added to a saturated solution of calcium carbonate.

(i) Balanced equation:

(ii)What evidence of a reaction will be observed? Explain.

(i) Balanced equation:

(ii) Is this a spontaneous reaction? Explain.