The Effect of Molecular Nature

Considering the requirements for ideal solution behavior. Section 13.6.1, we examine next the effect of the molecular characteristics of the mix- 

Consider a binary mixture where the intramolecular (1-1, and 2-2) forces are stronger than the intermolecular (1-2) ones. As a result, the presence of component 2 increases the escaping tendency of component 1, as compared to its value at the same composition, but in an ideal solution where all forces are equal and the same is the case with component 2. Both activity coefficients are, thus, greater than one. In such systems therefore (assuming ideal vapor behavior)  

Starting with ideal solution behavior, we note that since the total pressure is the sum of the two partial pressures  

Turning to positive deviations from Raoult s law, we note that the total pressure  

So far we have considered deviations from ideality resulting from differences among inter-(i-y) and intra-(H and j-j) molecular forces only. An other factor that can play an important role is the difference in free volume of the mixture components. The simplest way to define this quantity (Elbro et al, 1990) is in terms of what Bondi (1968) calls empty volume  

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