Exact Differentials and State Functions

Whenever the differential equation A2.2 can be equated with the differential of function F  

The state functions presented in section 2.4 are examples of exact differential functions of the type exemphfied by equation A2.3. Generally, reversible transformations in physical systems are described by equations of this type. 

Applying Schwarz s theorem on sequential differentiation of mixed derivatives  

Equation A2.10 represents a necessary and sufficient condition for equation A2.2 to be an exact differential and is valid for any couple of conjugate variables 

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