What is Gibb's Phase rule ?

The celebrated phase rule given by J. Willard Gibbs provides a general and useful relationship between the number of phases P, number of component C and the number of degree of freedom F, which must be specified in order to characterize a heterogenous system. According to Gibbs phase rule, a heterogenous system is not affected by gravity or by electrical and magnetic forces.

The Gibbs phase rule is stated as:

If a heterogenous system in equilibrium between any number of phases is influenced by temperature pressure and concentration only and not by gravity or electrical or magnetic forces or by surface action then the sum of number of phases P and degree of freedom F is greater than number of components C by two.