Introduction

Use the following steps to solve equilibria problems. Step 1 is probably the place where most people make the most mistakes, because it relies on recognizing if a reaction occurs and the nature of chemical species. Note that in many problems steps 3 and 4 are obvious and can be skipped.

1. First determine if any reactions will occur, and identify the species that will exist in equilibrium. Then determine the pre-equilibrium concentrations or partial pressures of the reactants and products that are involved in the equilibrium.
2. Write the balanced chemical reaction and the equilibrium constant expression.
3. Calculate the reation quotient, Q. Compare Q to K_eq to determine if the reaction will proceed in the forward or reverse directions to reach equilibrium.
4. Determine the changes in reactant and product concentrations or partial pressures to reach equilibrium.
5. Use the equilibrium constant expression to solve for the unknown, and then calculate the equilibrium concentrations or partial pressures.