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J. W. Hill, R. H. Petrucci, T. W. McCreary, & S. S. Perry General Chemistry, 4th edition.

Problem 14.62.

For the reaction CO(g) + H2O(g)CO2(g) + H2(g), Kc = 23.3 at 600 K. If 0.250 mol each of CO and H2O are introduced into a reaction vessel and equilibrium is established, how many moles each of CO2 and H2 will be present at equilibrium? (Hint: Does the volume of the reaction mixture matter?)




Answer:

Set up a table of concentrations and solve from there.
CO(g)
+
H2O(g)
CO2(g)
+
H2(g)
Initial
0.250
0.250
0
0
Change
–x
–x
+x
+x
Equilibrium
0.250–x
0.250–x
x
x

Note that the volume of the container does not matter in this problem (this is not always true):

Because the stoichiometry of the reactants and products is the same, the volume terms cancel out.

To solve the problem:

So the number moles of CO2 = the number of moles of H2 = 0.207 mol