Derivation of the Phase Rule: According to this rule, for any equilibrium thermodynamic system, the sum of the number of degrees of freedom(F) and the number of phases(P) are equal to the sum of number of independent component ‘C’ and the number of external factors n(T and P) affecting the physical state of the system. F+P=C+n Or , F+P= C+2 where ( n=2 ) Or , F= C-P+2 (Gibbs phase rule) Let us consider a heterogeneous system in equilibrium having C components (C 1 ,C 2 ,----C c ) distributed in P phase (P 1 , P 2 , ----P p ). The number of degree of freedom = Total number of variables - The number of factor define by the system Step-I : Determination of the total number of variables: Let us consider, a system which is having two component C 1 and C 2 . If the molar concentration of one component is known than that of other can be calculat