I would like to calculate the enthalpy of a pure compound with a cubic equation of state (the ones deriving from the Van der Waals equation of state).
I have an analytic expression of the heat capacity of the pure fluid in the perfect gas state as a function of temperature, allowing me to estimate the enthalpy of the pure fluid in the ideal gas state. Thus the cubic equation of state shall be used to estimate the deviation between the enthalpy of the pure fluid in the perfect gas state and the real state. And then come the questions:
- How to estimate this enthalpy deviation with a cubic equation of state?
- How to choose a wise enthalpy reference state (as no absolute enthalpy can be estimated I need to choose a reference enthalpy that might simplify some calculations)?
- How to treat the cases when wether I have (i) a single phase system or (ii) a two phase system (vapor-liquid equilibrium, i.e. how to take account of the phases proportions)?
I have read many references that give partial answers but none of them seem to tackle these questions in a single, clear and educationnal way. I hope someone is brave enough to try to answer all these questions.