Deduce the equilibrium expression (in terms of Keq) for homogeneous reactions occurring in solution

A homogeneous equilibrium has everything present in the same phase. The usual examples include reactions where everything is a gas, or everything is present in the same solution.

In writing an expression for equilibrium constant (Keq), we can start at a general case with the equation:

Where A,B,C and D are the chemical species involved and a.b.c and d are the coefficients in the balanced chemical equation. According to the law of mass action, the equilibrium condition is described by the expression:

If you allow this reaction to reach equilibrium and then measure the equilibrium concentrations of everything, you can combine these concentrations into an expression known as equilibrium constant.