Thermodynamic Properties of a Real Gas

In this section, we show how a knowled of p, V, T relations permits calculation of the thermodynamic properties of a real gas. The gas chosen as an example is perfluorocyclobutane, the thermodynamic properties of which have been calculated by Harrison and Douslin from p, P, T measurements by Douslin, Moore, and Waddington.  

Real-gas thermodynamic properties may be expressed as functions of the variables of state, according to relations which may be developed from first principles. A comprehensive list of such relations has been given by Beattie and Stockmayer. For example, the molar enthalpy H, the molar entropy S, and the molar Gibbs energy G of a real gas can be written in terms of p, T, and p (the amount density) as follows  

In these equations, the real-gas properties are expressed relative to the standard state values, H°, S°, and G°, which are, respectively, the molar enthalpy, the molar entropy, and the molar Gibbs energy values which the gas would have at a standard pressure p° (1.013 25 bar) if it were ideal. 

Douslin s experimental data consisted of values of the pressure, measured at fixed values of amount density between 0.75 and T.Okmol m and at rounded values of Celsius temperature (IPTS 48) between the critical temperature (115.22 °C) and 350 C. For application of equations (66) to (68) the pressure at each value of density was expressed in terms of temperature on the thermodynamic scale by a suitable function, which was then differentiated to obtain values for (pp T)p. After the values of the 

Harrison and D. R. Douslin, Perfluorocyclobutane the Thermodynamic Properties of the Real Gas, U.S. Dept, of the Interior, Bureau of Mines, Washington, 1964. 

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