Calculations for large or small values of K
Many reversible reactions have large or small values for their equilibrium constant, K. That is, one reaction (either the forward or the reverse) is much stronger than the other reaction. For instance, most acid-base reactions, precipitation reactions and redox reactions have either a very large or a very small K.
For reactions with intermediate values of K, determining the concentrations of the chemical species at equilibrium often leads to complex algebraic manipulations. However, when K is very large or very small, we can use a much simpler, two-step approach described here.
The two step approach simplifies the algebra and allows us to reason qualitatively about chemical reactions and their effects on the chemical concentrations. This qualitative reasoning is essential to understanding many applications of chemical equilibrium.