AP Chemistry: Gas Equilibrium
1) Give the equilibrium constant expression for each of the following:
a) 2H2(g) + O2(g) 2H2O(g)
b) SnO2(s) + 2H2(g)  Sn(s) + 2H2O(g)
2) PCl3(g) + Cl2(g) PCl5(g)
At a certain temperature, the following equilibrium concentrations were observed:
[Cl2] = 2.0 x 10-3 mol/L [PCl3] = 3.0 x 10-1 mol/L [PCl5] = 6.7 x 10-3 mol/L
a) Calculate the value of Kc at this temperature.
b) What is the value of Kc when the reaction is reversed?
c) In which direction will the system shift to reach equilibrium when the initial
concentrations are [Cl2] = 5.0 x 10-4M [PCl3]= 6.3 x 10-2M [PCl5]= 3.8 x 10-3 M
3) PCl3(g) + Cl2(g) PCl5(g)
In which direction will the position of equilibrium shift if the total pressure is increased
by halving the volume?
4) 2SO2(g) + O2(g)  2SO3(g)
Kc= 4.00 x 102 at 750oC. What concentration of SO2 must be in equilibrium with the
concentrations [O2] = 2.0 x 10-1M and [SO3] = 3.0M?
5) The synthesis of ammonia is exothermic. The value of K c for this equilibrium at 600K
is 4.1.
a) Calculate the Kp at 600K
b) Will the value of Kc be larger or smaller than 4.1 at 700K?
6) H2(g) + I2(g)  2HI(g)
H2(g) and I2(g) were mixed at 490oC and allowed to reach equilibrium. The following
equilibrium concentrations were found:
[H2] = 2.00M [I2] = 2.49 x 10-2M [HI] = 1.5 M
a) Calculate Kc
b) Calculate Kp
7) In another experiment at 490oC, 1.00 mol H2, 5.00 mol I2, and 2.50 mol of HI were
mixed in a 1.00 L vessel. When equilibrium was reached, the concentration of H 2 was
found to be 1.00 x 10-1 mol/L. Calculate the equilibrium concentrations of I 2 and HI.
8) Calculate the value of Kc at25oC for the reaction
CO2(g) + H2(g) CO(g) + H2O(l)
if the equilibrium concentrations of CO2 = H2 = CO = 0.10 M
9) Consider the reaction CaCO3(s)  CaO(s) + CO2(g) for which Kc = 8.0 x 10-3 at
750oC.
a) 1.00 mol of CaCO3(s) is sealed into a 5.0 L flask at 750oC. Calculate the equilibrium
concentration of CO2(g)
b) What fraction (by moles) of the original CaCO3(s) has decomposed?
c) How many moles of CaO(s) are produced?
d) Calculate Kp for this reaction at 750oC.
10) 2NO(g) + O2(g)  2NO2(g) (exothermic)
A study of this system at 25oC found the equilibrium concentrations to be
[NO] = 1.0 x 10-3 mol/L [O2] = 1.0 x 10-6 mol/L [NO2] = 1.3 mol/L
a) Calculate Kc at 25oC
b) Calculate Kp at 25oC
c) Predict the effect on the equilibrium position of the following stresses:
Increase the temperature
Increase the volume
Addition of Ne(g)
Addition of 1.0 mol of O2(g)
Addition of a catalyst
11) A 10.0 L flask contains 1.0 mol PCl5(g), 0.30 mol of PCl3(g) and 0.80 mol of Cl2(g) at
equilibrium. Calculate K for the reaction PCl5(g) PCl3(g) + Cl2(g)
12) Consider the reaction 2NH3(g)  N2(g) + 3H2(g)
At a temperature where Kc = 3.0 x 10-8. In an experiment, 1.0 x 10-3 mol NH3,
1.0 x 10-1 mol H2, and 1.0 mol N2 are mixed in a 5.0 L vessel.
a) Is the system at equilibrium?
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b) If not, in which direction must the system shift to reach equilibrium?
d) Represent the equilibrium concentrations in terms of the initial concentrations and
x.
13) The equilibrium constants KI and KII for the reactions
I. N2(g) + 3H2(g)  2NH3(g)
II. ½ N2(g) + 3/2 H2(g) NH3(g)
Are related as
a) KI = KII
b) KI = 1/KII
c) KII = KI½ d) KI = KII1/2
14) A quantity of N2O4 (g) is introduced into a flask at an initial pressure of 2.0 atm.
After the N2O4(g) has decomposed to NO2(g) and has come to equilibrium, the
pressure of N2O4 is 1.8 atm. Calculate Kp for the process.
N2O4(g)  2NO2(g)