Phase Rule

A generalization with regard to systems of chemical equilibrium discovered by Prof J Willard Gibbs It may be stated thus The degree of variableness number of degrees of freedom of a system is equal to the number of components minus the number of phases plus two Thus if the components be salt and water and the phases salt ice saturated solution and vapor the system is invariant that is there is only one set of conditions under which these four phases can exist in equilibrium If only three phases be considered the system is univariant that is the fixing of one condition as temperature determines the others