Fundamental Relations

Fundamental thermodynamic property relations for a fluid of constant composition are as follows:

    → I

    → II

    → III

    → IV

Criterion of exactness for a differential expression:

If , then the total differnential of F is defined as

    → V

Otherwise,

where,  and 

By further differentiation, we obtain

 and 

Since the order of differentiation in mixed second derivatives is immaterial, these equations give

    → VI

Equation VI serves as a criterion of exactness, when F is a function of x & y