When species in solution undergo multiple chemical reactions the solution may be treated as a solution of all species actually present or as a hypothetical solution composed of unreacted independent species. Based on the fundamental. thermodynamic principle the relationships of the mole numbers, the molar fractions, the thermodynamic properties and the partial molar properties between the hypothetical solution of unreacted independent species and the equilibrated solution of actual species have been established. The hypothetical solution provides a way of reducing the dimensionality of problem and simplifying the analysis.