Phase Equilibrium Condition for a Pure Substance

In the following section, the vapor-liquid phase equilibrium condition is derived for two different arrangements  

For both phases, mass transfer across the border between the phases is allowed. Introducing the chemical potential ii (see Eq. (C.81)), we obtain for both phases 

Applying Eqs. (C.lOl) and (C.102) to the particular phases and allowing mass transfer between the phases, we obtain 

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