11.1. VAPOR–LIQUID EQUILIBRIUM RELATIONS
11.1A. Phase Rule and Raoult's Law
As in the gas–liquid systems, the equilibrium in vapor–liquid systems is restricted by the phase rule, Eq. (10.2-1). As an example we shall use the ammonia–water, vapor–liquid system. For two components and two phases, F from Eq. (10.2-1) is 2 degrees of freedom. The four variables are temperature, pressure, and the composition yA of NH3 in the vapor phase and xA in the liquid phase. The composition of water (B) is fixed if yA or xA is specified, since yA + yB = 1.0 and xA + xB = 1.0. If the pressure is fixed, only one more variable can be set. If we set the liquid composition, the temperature and vapor composition are automatically set.
An ideal law, Raoult's law, can ...
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