VLE by Modified Raoults Law

For low to moderate pressures a much more reahstic equation for VLE results when the second major Raoult s-law assumptionis abandoned, and account is taken of deviations from solution ideality in the liquid phase by a factor inserted into Raoult s law, modified to read  

The factor yt is called an activity coefficient. Bnbblepointand dewpoint calculations made witli tliis equation are only a bit more complex than the same calculations made with Raoult s law. Activity coefficients are functions of temperature and liquid-phase composition, and ultimately are based on experiment (Sec. 12.1). For present purposes, the necessary values are assnmed 

Alternatively, Eq. (10.5) may be solved for xi, in which case sunmiiiig over all species yields  

Dewpoint and bubblepoint calculations are readily made witlr software packages such as Mathcad and Maple , in wliich iteration is an integral part of an equation-solving routine. Mathcad programs for solution of Ex. 10.3, parts ( aitlirough(d), are given in App. D,2. 

Calculations for multicomponent systems made without simplifying assumptions are readily carried out in like maimer by computer. The procedures are presented in Sec. 14.1. 

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