Transfer of two components from one phase to another

The discussion of the previous paragraph may now be extended to a binary system in which both components can pass from one phase to another. 

Equation (18.19) may now be applied successively to the two components. First we integrate A jT) from an initial state Tl, pi, (ir ) r=l corresponding to equilibrium between the phases 

Similarly by integrating (18.19) from an initial state consisting of pure component 2, we obtain 

In each case hrp and Vrp refer to the transfer of the component from the first to the second phase and can therefore be written 

We may choose p —p —p where p is an arbitrary pressure [e.g. 1 atm.) then T will be the temperature of coexistence, at pressure p, of the two phases in equilibrium when they both consist of pure component 1. In the same way T is the temperature of coexistence of pure 2 in the two phases at pressure p. Remembering that x — -X2, in each phase, we can then calculate x and x as a function of T andp. If we assume that both phases are ideal and that the latent heats are independent of temperature, then introducing the abbreviations  

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