Route A Vapor as Starting Phase

It is the most common approach to use the vapor as the starting phase when the y — ( -approach is used. It works as follows. 

Therefore, the enthalpy description is consistent with respect to chemical reactions. 

To calculate the enthalpy of a vapor, first the ideal gas enthalpy is calculated at system temperature T at P 0 using 

At this point, the transition from the pure components to the mixture takes place h T. P 0,Yi) = Y, P O) (6.57) 

Because of the ideal gas state, there is no excess term. 

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Use Route A (vapor as starting phase). Take the Peng-Robinson equation for the vapor phase calculations. cp and Ah can be taken from Appendix A. 

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