AP CHEMISTRY
CHAPTER 15: EQUILIBRIUM
PROBLEM SETS
Equilibrium Expressions and Calculations
*1.
Write expressions for Kc and Kp(whenever applicable) for the following reactions:
a. CO(g) + H2O(g) ↔ CO2(g) + H2(g)
b. HBr(aq) + H2O(l) ↔ H3O+ + Br-(aq)
c. (NH4)2Se(s) ↔ 2NH3(g) + H2Se(g)
d. AgCl(s) ↔ Ag+(aq) + Cl-(aq)
e. P4(s) + 6Cl2(g) ↔ 4PCl3(l)
*2.
The following equilibrium process has been studied at 230 ºC
2NO(g) + O2(g) ↔ 2NO2(g)
In one experiment the concentrations of reacting species at equilibrium are found to be
[NO] = 0.0542 M; [O2] 0.127 M; [NO2] = 15.5 M. Calculate the equilibrium constant
(Kc) of the reaction at this temperature.
*3.
Write the equilibrium-constant expressions for Kc and Kp (when applicable) for each of the
following reactions:
a. CO2(g) + H2(g) ↔ CO(g) + H2O(l)
b. SnO2(s) + 2CO(g) ↔ Sn(s) + 2CO2(g)
c. 2NO(g) + Cl2(g) ↔ 2NOCl(g)
*4.
A mixture of hydrogen and nitrogen gas in a reaction vessel is allowed to attain equilibrium at 472
ºC. The equilibrium mixture of gases was analyzed and found to contain 0.1207 M H2, 0.0402 M
N2, and 0.00272 M NH3. From these data calculate the equilibrium constant Kc and Kp for N2(g)
+ 3H2(g) ↔ 2NH3(g)
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AP CHEMISTRY
CHAPTER 15: EQUILIBRIUM
PROBLEM SETS
EQUILIBRIUM CONSTANT: BASIC CONCEPTS
*1.
Determine the value of Kp that corresponds to the following value of Kc:
CO(g) + Cl2(g) ↔ COCl2(g)
Kc = 1.2 x 103 at 668 K
2.
Determine the value of Kc that correspond to the following value of Kp:
SO2Cl2(g) ↔ SO2(g) + Cl2(g)
Kp = 2.9 x 10-2 at 303 K
3.
The equilibrium constant for the reaction
½ H2(g) + ½ I2(g) ↔ HI(g) at 718 K is 7.07.
a. What is the value of Kc at 718 K for the reaction: HI(g) ↔ ½ H2(g) + ½ I2(g) ?
b. What is the value of Kc at 718 K for the reaction H2(g) + I2(g) ↔ 2HI(g)?
4.
Determine Kc at 298 for the reaction 1/2N2(g) + ½ O2(g) + ½ Cl2 ↔ NOCl(g), given the
following data at 298 K:
1/2N2(g) + O2(g) ↔ NO2(g)
Kp = 1.0 x 10-9
NOCl(g) + ½ O2(g) ↔ NO2Cl
Kp = 1.1 x 102
NO2(g) + ½ Cl2(g) ↔ NO2Cl
Kp = 0.3
5.
A mixture of 5.000 x 10-3 mol of H2 and 1.000 x 10-2 mol of I2 is placed in a 5.000 L container at
448 ºC and allowed to come to equilibrium. Analysis of the equilibrium mixture shows that the
concentration of HI is 1.87 x 10-3 M. Calculate Kc at 448 ºC for the reaction:
H2(g) + I2(g) ↔ 2HI(g)
6.
Are the following reactions reactant- or product favored?
a) Cu(NH3)4+2 ↔ Cu+2(aq) + 4NH3(aq)
Cd(NH3)4+2 ↔ Cd+2(aq) + 4NH3(aq)
K = 1.5 x 10-13
K = 1.0 x 10-7
b) If each reaction in part (a) has a reactant concentration of 0.10 M, in which solution is
the NH3 concentration greater?
(1). Kp = 22
(5). Kc = 51
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(2) Kc = 1.17 x 10-3
(3) (a) 0.141 (b) 50.0
(4) Kc = 1.x10-11
(6) both are reactant favored, in solution 2 [NH3] is greater, explain.
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AP CHEMISTRY
CHAPTER 15: EQUILIBRIUM
PROBLEM SETS
EQUILIBRIUM CONSTANT: DETERMINING EQUILIBRIUM CONSTANT
1. The brown gas nitrogen dioxide, NO2, can form the colorless gas N2O4. K = 171 at 298 K.
Suppose the concentration of NO2 is 0.015M, and the concentration of N2O4 is 0.025 M. Is Q
larger than, smaller than, or equal to K? If the system is not at equilibrium, in which direction will
the reaction proceed to achieve equilibrium?
2. An aqueous solution of ethanol and acetic acid, each with a concentration of 0.810 M, is heated
to 100.0 ºC. At equilibrium, the acetic acid concentration is 0.748 M. Calculate K at this
temperature . The reaction is
CH3COOH(aq) + C2H5OH(aq) ↔ CH3COOC2H5(aq) + H2O(l)
3. Suppose a tank initially contains H2S with a pressure of 10.00 atm at 800. K. When the reaction
2H2S(g) ↔ 2H2(g) +S2(g)
Reaches equilibrium, the partial pressure of S2 vapor is 0.020 atm. Calculate Kp
(1) Q<K, not at equilibrium, thus the products will be favored.
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(2) K = 0.11 (3) 3.2 x 10-7
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AP CHEMISTRY
CHAPTER 15: EQUILIBRIUM
PROBLEM SETS
USING EQUILIBRIUM CONSTANTS IN CALCULATIONS
1.
A mixture of hydrogen and nitrogen gas in a reaction vessel is allowed to attain equilibrium at 472
ºC. The equilibrium mixture of gases was analyzed and found to contain 0.1207 M H2, 0.0402 M
N2, and 0.00272 M NH3. From these data calculate the equilibrium constant Kc and Kp for N2(g)
+ 3H2(g) ↔ 2NH3(g)
2.
A mixture of 5.000 x 10-3 mol of H2 and 1.000 x 10-2 mol of I2 is placed in a 5.000 – L container at
448 ºC and allowed to come to equilibrium. Analysis of the equilibrium mixture shows that the
concentration of HI is 1.87 x 10-3 M. Calculate Kc at 448 ºC for the reaction:
H2(g) + I2(g) ↔ 2HI(g)
3.
The equilibrium constant K = 55.64 for
H2(g) + I2(g) ↔ 2HI(g)
has been determined at 425 ºC. If 1.00 mole each of H2 and I2 are placed in a 0.500 L
flask at 425 ºC, what are the concentrations of H2, I2, and HI when equilibrium has been
achieved?
Quadratic equation w/o approximation
4. The equilibrium constant for the reaction
PCl5(g) ↔ PCl3(g) + Cl2(g)
has been determined at a given temperature and it was found to be K = 1.20. If the initial
concentration of PCl3 is 1.60 M, what will be the equilibrium concentration of reactant and
products?
Quadratic equation w approximation
5. The reaction
N2(g) + O2(g) ↔ 2NO(g)
contributes to air pollution whenever a fuel is burned in air at a high temperature, as in
gasoline engine. At 1500 K, K = 1.0 x 10-5. Suppose a sample of air has [N2] = 0.80
mol/L and [O2] = 0.20 mol/L before any reaction occurs. Calculate the equilibrium
concentration of reactants and products after the mixture has been heated to 1500 K.
1. ( Kc = 0.105; Kp = 2.81 x 10-5 )
(3) [H2]=[I2] = 0.42 M; [HI] = 3.16 M
(5) [N2] = 0.80 M; [O2] = 0.20 M; [NO] = 1.26 x 10-3 M
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2. Kc = 51
(4) [PCl5] = 0.69 M; [PCl3] = [Cl2] = 0.91 M
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AP CHEMISTRY
CHAPTER 15: EQUILIBRIUM
PROBLEM SETS
CHEMICAL EQUILIBRIUM: REVIEW SHEET
1. A sample of phosgene, COCl2(g), is introduced into a constant-volume vessel at 395 ºC and
observed to exert an initial pressure of 0.351 atm. When equilibrium is established, what will
be the partial pressure of each gas and what will be the total gas pressure?
CO(g) + Cl2(g) ↔ COCl2(g)
Kp = 22.5
2. At temperatures near 800ºC, steam passed over hot coke ( a form of carbon obtained from coal)
reacts to form CO and H2:
C(s) + H2O(g) ↔ CO(g) + H2(g)
The mixture of gases that results is an important industrial fuel called water gas (a) At 800 ºC,
the equilibrium constant for this reaction is Kc = 0.16. What are the equilibrium concentrations
of H2O, CO, and H2 in the equilibrium mixture at this temperature if we start with solid carbon
and 0.100 mol of H2O in a 1.00-L vessel? (b) What is the minimum amount of carbon required
to achieve equilibrium under these conditions? (c) What is the total pressure in the vessel at
equilibrium? (d) At 25 ºC, the value of Kc for this reaction is 7.0 x 10-23. Is the reaction
exothermic or endothermic? (e) To produce the maximum amount of CO and H2 at equilibrium,
should the pressure of the system be increased or decreased?
3. The pressure of the reacting mixture at equilibrium CaCO3(s) ↔ CaO(s) + CO2(g) is 0.105
atm at 350 ºC. Calculate Kp and Kc.
4. Consider the equilibrium 2NOBr(g) ↔ 2NO(g) + Br2(g)
If nitrosyl bromide, NOBr, is 34% dissociated at 25 ºC and the total pressure is 0.25 atm,
calculate Kp and Kc for the dissociation at this temperature.
5. Consider the following equilbria involving SO2(g) and thier corresponding equilbrium
constants.
SO2(g) + ½ O2(g) ↔ SO3(g)
K1
2SO3(g) ↔ 2SO2(g) + O2(g)
K2
Which of the following expressions relates K1 to K2?
(a) K2 = K12
(b) K22 = K1
(c) K2 = K1
(d) K2 = 1/K1
(e) K2 = 1/K12
1. Answer: Pco = PCl2 = 0.105 atm and Pcocl2 = 0.246 atm;
Ptotal = 0.456 atm
2. Answers: (a) [CO] = [H2] = 0.070 M; [H2O] = 0.030 M
(b)n At least 0.070 mol of C
( c) 15.0 atm
(d) endothermic ( K increases with temperature)
(e) To maximize the yield, the pressure must be decreased
3. Kp = 0.105; Kc = 2.05 x 10-3; 4. Kp = 9.6 x 10-3 ; Kc = 3.9 x 10-4; 5. (e)
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AP CHEMISTRY
CHAPTER 15: EQUILIBRIUM
PROBLEM SETS
LE CHÂTELLIER’S PRINCIPLE
1.
Describe the effect on equilibrium in the reaction of 1-octanol and acetic acid if water is removed
from the equilibrium mixture. Explain.
CH3(CH2)6CH2OH + CH3COOH ↔ CH3(CH2)6CH2OCOCH3 + H2O.
l-octanol
acetic acid
octyl acetate
2.
What would be the effect of each of the following changes on a constant-volume equlibrium
mixture of NH3, N2, and H2? Explain.
N2(g) + 3H2(g) ↔ 2NH3(g)
a. Adding H2(g)
3.
b. removing N2(g)
c. removing NH3(g)
An equilibrium mixture of SO2(g), O2(g), and SO3(g) is transferred from a 1.00 L flask to a 2.00 L
flask. In which direction does a net reaction proceed to restore equilibrium? Explain
2SO3(g) ↔ 2SO2(g) + O2(g)
4.
Is the amount of NO(g) formed from a given amounts of N2(g) and O2(g) greater at high or low
temperatures? Explain.
N2(g) + O2(g) ↔ 2NO(g)
5.
ΔH = +180.5 kJ
Flask A, pictured below, contains an equilibrium mixture in the reaction represented by the
following equation:
CO(g) + H2O(g) ↔ CO2(g) + H2(g)
ΔH = -41 kJ; Kc = 9.03 at 698 K
Flask A is connected to flask B, and a new equilibrium is established when the valve between the
two is opened. Describe, qualitatively, how the amounts of CO, H2O, CO2, and H2 in the new
equilibrium compare to their amounts in the initial equilibrium when the contents of flask B are
those listed below. If you are uncertain, explain why.
a. Flask B contains Ar(g) at 1 atm pressure
b. Flask B contains 1.0 mol CO2.
Eq. Mixture
CO, H2O,
CO2, and H2
A
B
c. Flask B contains 1.0 mol CO, and the temperature of the A-B assembly is raised by 100 ºC.
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AP CHEMISTRY
CHAPTER 15: EQUILIBRIUM
PROBLEM SETS
14.28
The pressure of the reacting mixture at equilibrium CaCO3(s) ↔ CaO(s) + CO2(g) is 0.105 atm
at 350 ºC. Calculate Kp and Kc.
Answer: Kp = 0.105; Kc = 2.05 x 10-3
14.25
Consider the equilibrium 2NOBr(g) ↔ 2NO(g) + Br2(g)
If nitrosyl bromide, NOBr, is 34% dissociated at 25 ºC and the total pressure is 0.25 atm, calculate
Kp and Kc for the dissociation at this temperature.
Answer: Kp = 9.6 x 10-3 ; Kc = 3.9 x 10-4
Problem set Equilibrium
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AP CHEMISTRY
Problem set Equilibrium
2/16/2016
CHAPTER 15: EQUILIBRIUM
PROBLEM SETS
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