Chemistry 106, Chapter 12 Exercises
Equilibrium Constant Expressions
1. Write equilibrium constant expressions for the following reactions.
a. I2(g) + 5F2(g) ↔ 2IF5(g)
b. CO(g) + 2H2(g) ↔ CH3OH(l)
c. CH4(g) + H2O(l) ↔ CO(g) + 3H2(g)
d. 2NO3-(aq) + 8H+(aq) + 3Cu(s) ↔ 2NO(g) + 3Cu2+ + 4H2O(l)
e. Ca2+(aq) + CO32-(aq) ↔ CaCO3(s)
Answers
a. K 
( PIF 5 ) 2
( PI 2 )( PF 2 )5
d. K 
( PNO ) 2 [Cu 2 ]3

[ NO3 ]2 [ H  ]8
b. K 
1
( PCO )( PH 2 ) 2
e. K 
c. K 
( PCO )( PH 2 )3
( PCH 4 )
1
2
[Ca ][CO3 ]
2
Determining Equilibrium Constants (K's) from other K's
2. At 25oC, K = 2.2 x 10-3 for the following reaction.
ICl(g) ↔ 1/2 I2(g) + 1/2Cl2(g)
a. Calculate K at 25oC for the decomposition of ICl into one mole of iodine and one mole of
chlorine. Ans. 4.8 x 10-6
b. Calculate K for the formation of two moles of ICl(g). Ans. 2.1 x 105
3. At 627oC, K = 0.76 for the following reaction.
2SO2(g) + O2(g) ↔ 2SO3(g)
a. Calculate K at 627oC for the synthesis of of one mole of sulfur trioxide gas. Ans. 0.87
b. Calculate K for the decomposition of two moles of SO3. Ans. 1.3
4. Given the following reactions and their equilibrium constants,
H2O(g) + CO(g) ↔ H2(g) + CO2(g) K = 1.6
FeO(s) + CO(g) ↔ Fe(s) + CO2(g) K = 0.67
calculate K for the following reaction.
Fe(s) + H2O(g) ↔FeO(s) + H2(g)
Ans. K = 2.4
5. Given the following reactions and their equilibrium constants,
C(s) + CO2(g) ↔ 2CO(g) K = 2.4 x 10-9
COCl2(g) ↔ CO(g) + Cl2(g) K = 8.8 x 10-13
calculate K for the following reaction.
C(s) + CO2(g) + 2Cl2(g) ↔ 2COCl2(g)
Ans. 3.1 x 1015
6. Given the following reactions and their equilibrium constants,
2N2(g) + O2(g) ↔ 2N2O(g) K = 1.2 x 10-35
N2O4(g) ↔ 2NO2(g) K = 4.6 x 10-3
1/2N2(g) + O2(g) ↔ NO2(g) K = 4.1 x 10-9
calculate K for the following reaction.
N2O(g) + 3/2O2(g) ↔ N2O4(g)
Ans. 1.1 x 103
7. Given the following reactions and their equilibrium constants,
2NO(g) ↔ N2(g) + O2(g) K = 1 x 10-30
2NO(g) + Br2(g) ↔ 2NOBr(g) K = 8 x 101
calculate K for the following reaction.
1/2N2(g) + 1/2O2(g) + 1/2Br2(g) ↔ NOBr
Ans. 9 x 1015
Calculating K's from Data
8. When carbon monoxide and hydrogen gas react, methane and steam are formed.
CO(g) + 3H2(g) ↔ CH4(g) + H2O(g)
At 1127oC, analysis at equilibrium shows that PCO = 0.921 atm, PH2 = 1.21 atm, PCH4 = 0.0391 atm,
and PH2O = 0.0124. What is the equilibrium constant for this reaction? Ans. 2.97 x 10-4
9. Calculate K for the formation of methyl alcohol at 100oC.
CO(g) + 2H2(g) ↔ CH3OH(g)
At equilibrium the partial pressures of the gases are PCO = 0.814 atm, PH2 = 0.274 atm, and PCH3OH =
0.0512 atm. Ans. 0.838
10. Consider the following reaction.
2SO3(g) ↔ 2SO2(g) + O2(g)
Initially, a sealed flask has 0.541 atm of SO3 at 1000 K . After equilibrium is established, the partial
pressure of oxygen is measured to be 0.216 atm. Calculate K for this reaction. Ans. 3.39
11. Consider the decomposition of ammonium hydrogen sulfide.
NH4HS(s) ↔ NH3(g) + H2S(g)
Initially a sealed flask at 25oC contains 10.0g of NH4HS, NH3(g) at a pressure of 0.692 atm, and
H2S(g) at a pressure of 0.0532 atm. When equilibrium is established, it is found that partial pressure
of NH3 has increased by 12.4%. Calculate K for this reaction. Ans. 0.108
Predicting the Direction of Reaction
12. A gaseous reaction mixture contains 0.30 atm SO2, 0.16 atm Cl2, and 0.50 atm SOCl2 in a 2.0 L
container. K = 0.011 for the following equilibrium system.
SOCl2(g) ↔ SO2(g) + Cl2(g)
a. Calculate Q.
b. Is the system at equilibrium?
c. If the system is not at equilibrium, in which direction will the system move to reach equilibrium?
Ans. a. Q = 0.096 b. no c. left
13. K for the following system is 26 at 300oC.
PCl5(g) ↔ PCl3(g) + Cl2(g)
In a 5.0 L flask, a gaseous mixture consists of all three gases with the following partial pressures,
PPCl5 = 0.012 atm, PCl2 = 0.45 atm, PPCl3 = 0.90 atm.
a. Calculate Q.
b. Is the system at equilibrium?
c. If not, which way will the equilibrium shift?
Ans. a. Q = 34 b. no c. left
14. The reversible reaction between hydrogen chloride gas and one mole of oxygen gas produces steam
and chlorine gas.
4HCl(g) + O2(g) ↔ 2Cl2(g) + 2H2O(g)
K = 0.79
Predict the direction in which the system will move to reach equilibrium in each of the following
situations.
a. PH2O = PHCl = PO2 = 0.20 atm and PCl2 = 0
b. PHCl = 0.30 atm, PH2O = 0.35 atm, PCl2 = 0.2 atm, PO2 = 0.15 atm
Ans. a. Q = 0, right b. Q = 4, left
15. Consider the following equilibrium.
2NO2(g) ↔ 2NO(g) + O2(g)
K = 0.50
Predict the direction in which the system will move to reach equilibrium in each of the following
situations.
a. PO2 = PNO = PNO2 = 0.10 atm
b. PNO2 = 0.0848 atm, PO2 = 0.0116 atm, PNO = 0
c. PNO2 = 0.20 atm, PO2 = 0.010 atm, PNO = 0.040 atm
Ans. a. Q = 0.1, right b. Q = 0, right c. Q = 4 x 10-4, right
K and Equilibrium Pressures
16. Consider the reaction between ammonia and oxygen.
4NH3(g) + 3O2(g) ↔ 2N2(g) + 6H2O(g)
At a certain temperature, K = 0.0049. Calculate the equilibrium partial pressure of ammonia if PN2 =
0.213 atm, PH2O = 0.883 atm, and PO2 = 0.255 atm at equilibrium. Ans. PNH3 = 4.0 atm
17. At 500 oC, K for the formation of ammonia from nitrogen and hydrogen gases is 1.5 x 10-5.
N2(g) + 3H2(g) ↔ 2NH3(g)
Calculate the equilibrium partial pressure of hydrogen if the equilibrium partial pressures of
ammonia and nitrogen are 0.015 and 1.2 atm, respectively. Ans. PH2 = 2.3 atm
18. At a certain temperature, K is 1.3 x 105 for the following reaction.
2H2(g) + S2(g) ↔ 2H2S(g)
What is the equilibrium pressure of hydrogen sulfide if those of hydrogen and sulfur gases are 0.106
atm and 0.417 atm, respectively? Ans. PH2S = 24 atm
19. K for the following reaction is 0.040.
2BrCl(g) ↔ Br2(g) + Cl2(g)
An equilibrium mixture contains bromine and chlorine gases at equal partial pressures of 0.0493
atm. What is the equilibrium partial pressure of bromine chloride? Ans. PBrCl = 0.25
20. Carbonyl fluoride, COF2, is an important intermediate for organic fluorine compounds. It can be
prepared by the following reaction:
CO2(g) + CF4(g) ↔ 2COF2(g)
At 1000oC, K for this reaction is 0.50. What are the partial pressures of all the gases at equilibrium
when the initial pressures of CO2 and CF4 are 0.713 atm? Ans. PCO2 = PCF4 = 0.52 atm, PCOF2 = 0.38
atm
21. At a certain temperature, K for the following reaction is 0.0255.
N2(g) + O2(g) ↔ 2NO(g)
What are the partial pressures of all gases at equilibrium if the initial partial pressure of the gases
(both reactants and products) is 0.300 atm? Ans. PN2 = PO2 = 0.417 atm, PNO = 0.067 atm
22. The reaction below has a K = 1.30 at 650 oC.
CO(g) + H2O(g) ↔ H2(g) + CO2(g)
Carbon monoxide and steam both have initial partial pressures of 0.485 atm, while hydrogen and
carbon dioxide start with partial pressures of 0.159 atm. Calculate the partial pressures of each gas
at equilibrium. Ans. PH2 = PCO2 = 0.343 atm, PH2O = PCO = 0.300 atm
23. Hydrogen cyanide, a highly toxic gas, can decompose to cyanogens and hydrogen gases,
2HCN(g) ↔ C2N2(g) + H2(g)
At a certain temperature, K for this decomposition is 0.17. What are the partial pressures of all gases
at equilibrium if initially the partial pressures are PC2N2 = PH2 = 0.32 atm, PHCN = 0.45 atm? Ans
PC2N2 = PH2 = 0.24 atm, PHCN = 0.60 atm
24. At 800 K, hydrogen iodide can decompose into hydrogen and iodine gases.
2HI(g) ↔ I2(g) + H2(g)
At this temperature, K = 0.0169. What are the partial pressures at equilibrium of the hydrogen and
iodine if initially a sealed flask contains only HI at a pressure of 0.200 atm? Ans. PI2 = PH2 = 0.021
LeChatelier's Principle
25. Consider the following system.
SO3(g) ↔ SO2(g) + ½O2(g) ΔH = 98.9 KJ
Which way will the equilibrium shift if the equilibrium is disturbed in the following way?
a. O2 is added.
b. The system is compressed at constant temperature.
c. Ar gas is added.
d. SO2 is removed.
e. The temperature is decreased.
Ans. a. left
b. left
c. no effect
d. right
e. left
Which of the above factors increase K? Which will decrease K?
Ans. none will increase K, e will decrease K
26. Consider the following system.
4NH3(g) + 3O2(g) ↔ 2N2(g) + 6H2O(l)
ΔH = -1530.4 KJ
Which way will the equilibrium shift and how will the amount of ammonia be affected if the
equilibrium is disturbed in the following manner?
a. O2 is removed.
b. N2 is added.
c. Water is added.
d. The container is expanded at constant temperature.
e. The temperature is increased.
Ans. a. left, increase
b. left, increase
c. no effect
d. left, increase
e. left, increase
Which of the above factors will increase K? Which will decrease K?
Ans. none will increase K, e with decrease K
27. Predict the direction in which each of the following equilibria will shift if the pressure on the system
is increased by compression?
a. H2O(g) + C(s) ↔ CO(g) + H2(g)
b. SbCl5(g) ↔SbCl3(g) + Cl2(g)
c. CO(g) + H2O(g) ↔ CO2(g) + H2(g)
Ans. a. left
b. left
c. no effect
28. Predict the direction in which each of the following equilibria will shift if the pressure on the system
is decreased by expansion?
a. Ni(s) + 4CO(g) ↔ Ni(CO)4(g)
b. ClF5(g) ↔ ClF3(g) + F2(g)
c. HBr(g) ↔ ½H2(g) + ½Br2(g)
Ans. a. left
b. right
c. no effect
29. At a certain temperature nitrogen and oxygen combine in the following way.
N2(g) +O2(g) ↔ 2NO(g)
At equilibrium the partial pressures of N2, O2, and NO were determined to be 31.3, 31.3, and 5.0 atm
respectively. K = 0.0255 for this reaction. If enough NO is added to increase its partial pressure from 5.0
atm to 8.0 atm what are the partial pressures when equilibrium is reestablished? Ans. PN2 = PO2 = 32.7
atm and PNO = 5.2 atm.
30. Iodine chloride decomposes at high temperatures to iodine and chlorine gases.
2ICl(g) ↔ I2(g) + Cl2(g)
Equilibrium is established at a certain temperature when the partial pressure of ICl is 0.43 atm and
the partial pressures of I2 and Cl2 are both 0.31 atm. K = 0.23. If enough ICl is removed to decrease
its partial pressure to 0.30 atm, in which direction will the reaction shift? What are the partial
pressures when equilibrium is reestablished? Ans. left, PICl = 0.46 atm , PI2 = 0.23 atm, PCl2 = 0.23
atm.
31. Carbonylbromide (COBr2) can be formed by combining carbon monoxide and bromine gas.
CO(g) + Br2(g) ↔ COBr2(g)
At equilibrium, the partial pressures of COBr2, CO and Br2 are 0.12, 1.00, and 0.65 atm,
respectively. K = 0.18.
Enough bromine condenses to decrease its partial pressure to 0.50 atm. Which way will the
equilibrium shift? What are the partial pressures of all gases after equilibrium is reestablished?
Ans. left, PCO = 1.02 atm, PBr2 = 0.52 atm, PCOBr2 = 0.10 atm