2. Predicting liquid-vapor equilibria

2.1 Perfect gases and ideal solutions

Dalton's and Raoult's laws are valid whatever the composition of the mixture. Knowledge of the liquid-vapor equilibria of pure substances (Antoine's law, for example) is sufficient to predict equilibria (binary or multicomponent): if X _J designates the molar (or mass) fraction of the J-th component in the aqueous phase and Y _J the molar (or mass) fraction of the J-th component in the vapor phase, the relative volatilityα is defined by the relation : $\alpha =\frac{Y_1/Y_2}{X_1/X_2}$

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