The thermodynamic stability of solutions or Gibbs free energy is determined both the enthalpy and the entropy terms. It is well known that in binary melts of alkali metal halides with a common ion, the enthalpy of mixing is usually small and is up to a kilojoule per mole, so these solutions are close to ideal. The maximum entropy of mixing and hence the minimum free energy of mixing is usually realized in the case of a solution in which the components have equal mole fractions . The chemical formula for a solution of n components with equal mole fractions (xi=1/n) can be written as follows: