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
![1st expression vapor props Ideal Thermo Example](https://www.colan.org/wp-content/uploads/2016/08/VaporPhaseProperties01.jpg)
Entropy of the vapor phase follows from
![2nd equation Vapor Properties Ideal Thermo example](https://www.colan.org/wp-content/uploads/2016/08/VaporPhaseProperties02-300x57.jpg)
Fugacity coefficient of all components is unity, corresponding to an ideal gas. Fugacity for the vapor phase therefore is:
![3rd equation Vapor Props Ideal Thermo example](https://www.colan.org/wp-content/uploads/2016/08/VaporPhaseProperties03.jpg)