The Gibbs-Duhem equation applied to activity coefficients

The Gibbs-Duhem equation applied to activity coefficients 

In 7 1 we obtained the following form of the Gibbs-Duhem equation as applied to a two-component solution in which the mole fractions are and x  

Performing the necessary differentiations and substituting in (9 39) we obtain the following alternative form of the Gibbs-D em 

This relationf shows that the activity coefficients are not independent. 

Any empirical or theoretical equations which purport to express the activity coefficients as functions of composition must be such as will satisfy (9 40). Typical of such equations are those of Maigules and van Laar discus in 7 8. 

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