The Thermodynamic Functions 0, P, and

The basis thermodynamic functions for pure (single-component) systems are the specific volume (V = VN/N), temperature (T), specific internal energy U = UN/N), pressure (P), and specific entropy S = SN/N). Note that N is Avogadro s number and N is the total number of molecules. All other thermodynamic functions can be expressed in terms of these basis functions for example, H (enthalpy) = t) +,  

By definition, the internal energy for a S3rstem at equilibrium is the average total energy in the S3rstem, i.e., 

Substituting Eq. (4.30) into Eq. (4.35) and carrying out the momentum integrations (see Prob. 4.1) gives 

Alternatively, using Eqs. (4.30) and (4.36) can be reexpressed in terms of the configurational integral as 

The (Gibbs) entropy So for a classical system is defined in the canonical ensemble as  

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