In the Ideal Thermodynamic example, the vapor phase is governed by the ideal gas law (PV = RT). The enthalpy reference state is in the (ideal) vapor phase at Tref = 298.15 K. Reference pressure is required for entropy, and is Pref = 101325 Pa. Volume and density of the vapor phase follow from the ideal gas law. Enthalpy of the vapor phase follows from
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Entropy of the vapor phase follows from
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Fugacity coefficient of all components is unity, corresponding to an ideal gas. Fugacity for the vapor phase therefore is:
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