Relation between the activity coefficients of a binary solution

Relation between the Activity Coefficients of a Binary Solution. 

Just as in 7 of chapter XX we can show that it is sufficient to know the activity coefficient of one component of a binary solution in order to calculate the activity coefficient of the other. This fact is of importance when only one of the two components has a measurable vapour pressure. 

The state of a binary solution may be determined by the variables T, p, X2, so that equation (20.58) can be written in the form 

Let us assume that In yj can be represented by the power series (21.40) with Aj 2 then the above equation can be written 

The constant of integration I is determined from the fact that when X2 = l, 72 — 1 hence 

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