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.
- 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.
- Write the balanced chemical reaction and the equilibrium constant expression.
- Calculate the reation quotient, Q. Compare Q to Keq to determine if the reaction will proceed in the forward or reverse directions to reach equilibrium.
- Determine the changes in reactant and product concentrations or partial pressures to reach equilibrium.
- Use the equilibrium constant expression to solve for the unknown, and then calculate the equilibrium concentrations or partial pressures.