1. The document outlines the general procedure for solving equilibrium problems which includes: tabulating initial and equilibrium concentrations, calculating concentration changes, using stoichiometry to determine other concentration changes, calculating equilibrium concentrations, and computing the equilibrium constant Keq. 2. It then provides 5 example equilibrium problems to solve using this procedure, involving reactions of ammonia dissolving in water, sulfur trioxide decomposing, calcium chromate dissolving, the Haber process of nitrogen and hydrogen reacting to form ammonia, and a general reaction of reactants A and B forming products C and D.

1. Worksheet 11. Equilibrium Calculations (Part A)
Concept:
General Procedure in Solving Equilibrium Problems
1. Tabulate the known initial and equilibrium concentrations of all species in the
equilibrium-constant expression.
2. For those species for which both the initial and equilibrium concentrations are
known, calculate the change in concentration that occurs as the system reaches
equilibrium.
3. Use the stoichiometry of the reaction (that is, use the coefficients in the balanced
chemical equation) to calculate the changes in concentration for all the other
species in the equilibrium.
4. From the initial concentrations and the changes in concentration, calculate the
equilibrium concentrations.
5. Compute Keq.
1. Enough ammonia is dissolved in 5.00 liters of water at 250 C to produce a solution that is
0.0124 M in ammonia. The solution is then allowed to come to equilibrium. Analysis of the
equilibrium mixtures shows that the concentration of OH – is 4.64 x 10 –4 M. Calculate the Keq
at 25 0C for the reaction. (Brown et al. p. 589)
NH3 (aq) + H2O (l) NH4 + (aq) + OH - (aq)
2. Sulfur trioxide decomposes at high temperature in a sealed container:
2 SO3 (g) 2 SO2 (g) + O2 (g)
Initially, the vessel is charged at 1000 K with SO3 (g) at a partial pressure of 0.500 atm. At
equilibrium, the SO3 partial pressure is 0.200 atm. Calculate the value of Keq at 1000 K. (Brown et
al. p. 590)
3. At 25 0C, the reaction: CaCrO4 (s) Ca 2+ (aq) + CrO4 2- (aq)
has an equilibrium constant Keq = 7.1 x 10 –4. What are the equilibrium concentrations of Ca 2+
and CrO4 2- in a saturated solution of CaCrO4. (Brown et al. p. 607)
3. For the Haber process:
N2 (g) + 3H2 (g) 2 NH3 (g)
Keq = 1.45 x 10 –5 at 500 0C. In an equilibrium mixture of the three gases at 500 0C, the partial
pressure of H2 is 0.928 atm and that of N2 is 0.432 atm. What is the partial pressure of NH3 in the
equilibrium mixture? (Brown et al. p. 592)
5. Given the following initial concentrations for the reaction:
A (aq) + B (aq) C (aq) + D (aq) Keq = 49.0
0.200 M 0.200 M 0M 0M
Calculate the equilibrium concentrations of all the reaction species.