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AP Chemistry
Worksheet : Test review
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No calculator problems :
_____ 1. For the reaction A(g) + 2B(g) ↔ C(g), 3.00 mol of A and 3.00 mol of B are placed in a 5.00 L
vessel. At equilibrium the concentration of C is 0.200 M. What is the value of K?
a. 2.50
b. 0.180
c. 12.5
d. 31.3
e. 6.5
_____ 2. 2NO(g) + O2(g) ↔ 2 NO2(g)
K = 60.
Which of the following would be true if 0.2 mol NO, 0.4 mol O2 and 0.6 mol of NO2 are placed in a
2.0 L vessel at a constant temperature.
a.
b.
c.
d.
e.
The system will remain unchanged.
The concentration of nitrogen dioxide will, increase.
The concentration of nitrogen dioxide will decrease.
The value of K will increase.
Not enough information is given.
_____ 3. Equal masses of three different ideal gases, X, Y, and Z, are mixed in a sealed rigid container. The
total pressure is measured to be 9.0 atm. If the temperature of the system remains constant, which of
the following statements about the partial pressure of gas X is correct?
(A) It depends on the volume of the container
(B) It depends on the intermolecular forces of attraction between molecules of X, Y, and Z.
(C) It depends on the relative molecular masses of X, Y, and Z.
(D) It depends on elasticity of molecular collisions.
(E) It is equal to 3.0 atm.
_____ 4. In an ideal solution at 25 °C, the vapor pressure of toluene is 32 millimeters of mercury and that of
benzene is 28 millimeters of mercury. What is the mole fraction of benzene in the vapor in
equilibrium with this solution?
(A) 0.88
(C) 0.47
(E) 0.95
(B) 0.53
(D) 0.78
_____ 5. When the actual gas volume is less then the volume predicted by the ideal gas law, the explanation
lies in the fact that the ideal gas law does not include a factor for molecular
(A) volume
(C) velocity
(E) shape
(B) mass
(D) attractions
_____ 6. When 16.1 g magnesium is reacted with excess HCl, 47 kJ of energy is released as heat. What is
ΔH for this reaction per mole of Mg consumed?
a. -31 kJ
b. +31 kJ
c. -71 kJ
d. +71 kJ
e. +22 kJ
13-Test Review
_____ 7. Given : X2Y(s) + ½ Y2(g)  2 XY(s)
X2Y(s)  X(s) + XY(s)
ΔHº = -125 kJ
ΔHº = +28 kJ
Calculate the standard enthalpy of formation for XY(s)
a. -97 kJ/mol
b. +97 kJ/mol
c. +299 kJ/mol
d. +155 kJ/mol
e. -153 kJ/mol
_____ 8. What is the standard heat of formation of methane, ∆Hf CH4(g), as calculated from the data below?
CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(l)
∆Hf H2O(l) = –286 kJ/mol
a. –210. kJ/mole
b. –108 kJ/mole
c. –76 kJ/mole
∆H = –889 kJ
∆Hf CO2(g) = –393 kJ/mol
d. 76 kJ/mole
e. 210. kJ/mole
_____ 9. For which process is ΔS negative?
a. evaporation of 1 mol of CCl4 (l)
b. mixing 5 mL ethanol with 25 mL water
c. compressing 1 mol Ne at constant temperature from 1.5 L to 0.5 L
d. raising the temperature of 100 g Cu from 275 K to 295 K
e. grinding a large crystal of KCl to powder
10. Hydrogen for use in ammonia production is produced by the reaction CH4(g) + H2O(g) ↔ CO(g) + 3H2(g)
What will happen to a reaction mixture at equilibrium if
a. H2O(g) is removed?
b. The temperature is increased (the reaction is endothermic)?
c. An inert gas is added?
d. CO(g) is removed?
e. The volume of the container is tripled?
11. What will happen to the number of moles of SO3 in equilibrium with SO2 and O2 in the reaction
2SO3(g) ↔ 2SO2(g) + O2(g)
ΔH= 197 kJ
in each of the following cases?
a. Oxygen gas is added.
b. The pressure is increased by decreasing the volume.
c. The pressure is increased by adding argon gas.
d. The temperature is decreased.
e. Gaseous sulfur dioxide is removed.
13-Test Review
Calculator problems :
12. At 25°C, Kp = 1 x 10-31 for the reaction N2(g) + O2(g) ↔ 2NO(g)
Calculate the concentration of NO, in molecules/cm3, that can exist in equilibrium in air at 25°C. In air,
PN2= 0.8 atm and Po2 = 0.2 atm.
13. At a certain temperature, K = 9. 1 x 10-4 mol/L for the reaction FeSCN2+ ↔ Fe3+ + SCNCalculate the concentrations of Fe3+, SCN-, and FeSCN2+ in a solution which is initially 2.0 M FeSCN2+.
14. Nitric oxide and bromine at initial partial pressures of 98.4 and 41.3 torr, respectively, were allowed to
react at 300. K. At equilibrium the total pressure was 110.5 torr. The reaction is
2NO(g) + Br2(g) ↔ 2NOBr(g)
Calculate the value of Kp.
15. At 25°C, Kp = 5.3 x 105 atm-2 for the reaction N2(g) + 3H2(g) ↔ 2NH3(g). When a certain partial
pressure of NH3(g) is put into an otherwise empty rigid vessel at 25°C, equilibrium is reached when 50.0%
of the original ammonia has decomposed. What was the original partial pressure of ammonia before any
decomposition occurred?(Solve for P0 in terms of xfirst and then plug in and solve).
13-Test Review
16. Consider the reaction P4(g) ↔ 2P2(g) where Kp = 1.00 x 10-1 atm at 1325 K. In an experiment where P4(g)
was placed into a container at 1325 K, the equilibrium mixture of P4(g) and P2(g) has a total pressure of
1.00 atm. Calculate the equilibrium pressures of P4(g) and P2(g). Calculate the fraction (by moles) of P4(g)
that has dissociated to reach equilibrium.
17. The partial pressures of an equilibrium mixture of N2O4(g) and NO2(g) are PN2o4 = 0.33 atm and PNo2 = 1.2
atm at a certain temperature. The volume of the container is doubled. Find the partial pressures of the two
gases when a new equilibrium is established.
18. At 125°C, Kp = 0.25 atm2 for the reaction 2NaHCO3(s) ↔ Na2CO3(s) + CO2(g) + H2O(g)
A 1.00-L flask containing 10.0 g NaHCO3 is evacuated and heated to 125°C.
a. Calculate the partial pressures of CO2 and H2O after equilibrium is established.
b. Calculate the masses of NaHCO3 and Na2CO3 present at equilibrium.
c. Calculate the minimum container volume necessary for all of the NaHCO3 to decompose.
Answers : 1. c 2. b 3. c 4. c 5. d 6. c 7. e 8. c 9. c 10a. L, 10b. R 10c. no change 10d. R 10e. R
11a. increase, shift left 11b. increase, shift left 11c no change 11d. increase, shift left 11e. decrease,
shift right 12. 2 x 103 molecules/cm3 13. FeSCN2+ = 2.0 M, Fe3+ and SCN- = 0.043 M 14. 134 atm-1
15. 2.1 x 10-3 atm 16. PP4 = 0.73 atm, PP2 = 0.270 atm, 16% P4 is dissociated
17. PNO2 = .71 atm,
PN2O4 = .11 atm 18a. 0.50 atm 18b. 7.5 g NaHCO3, 1.6 g Na2CO3 18c. 3.9 L
13-Test Review