Extended corresponding states expressions for the changes in enthalpy, compressibility factor and constant-volume heat capacity at vaporization

By analyzing data for the vapor pressure curve of 121 fluids considered by the National Institute of Standards and Technology (NIST) program RefProp 9.1, we find that the first and the second derivatives with respect to reduced temperature (Tr) of the natural logarithm of the reduced vapor pressure at the acentric point (Tr=0.7) show a well defined behavior with the acentric factor ω. This fact is used for checking some well-known vapor pressure equations in the extended Pitzer corresponding states scheme. In this scheme, we then obtain analytical expressions for the temperature dependence of the enthalpy of vaporization and the changes in the compressibility factor and the constant-volume heat capacity along the liquid-vapor coexistence curve. Comparisons with RefProp 9.1 results are presented for argon, propane and water. Furthermore, very good agreement is obtained when comparing with experimental data of perfluorobenzene and perfluoro-n-heptane.