Analytical treatment of the critical properties of a generalized van der Waals equation

The two-parameter van der Waals (vdW) equation of state is generalized, by adding another two parameters to the attractive term. General relations between thermodynamic functions of the generalized vdW equation and the hard sphere gas are derived. The cubic equation of the generalized vdW is solved and the critical points (P c , V c , T c ) are obtained for general k. The critical properties of the vdW real gas such as the isothermal compressibility K T , the isobaric expansion coefficient α and the isobaric heat capacity C P are calculated exactly. The temperature dependence of K T , α and C P is investigated close to the critical point on the critical isobar path P r = 1(P = P c ). Numerical calculations for K T and C P are presented above and below P r .