Thermodynamic Excess Function of r-mer mixtures

In 2 we expressed the Gibbs free energy of an r-mer mixture in the same form as the Gibbs free energy of a pure r-mer system. Hence the excess free energy and its derivatives can be written in a very simple form. For example, from (17.2.14) and (16.7.10) we obtain for G (as usual at zero pressure) 

The last term of (17.4.1) is the combinatorial excess free energy we have already studied in Ch. III. It correqwnds to a purdy aitropic effect. We shall note it by 

Inspecting these relations we see that the origin of the excess properties has to be found in the following three effects  

The excess properties of r-mer mixtures are thus much more intricate than those of monomer mixtures. The geometrical effect has already been discussed in Ch. Ill, 5-7. It does not interfere with effects (2) and (3) in the excess properties (when one assumes rauidom mixing). The effects (2) and (3) both appear through the reduced temperature 

We have already noted that the geometrical effect (1) affects primarily the entropy of mixing. On the other hand, the effects (2) and (3) are related to the changes in the reduced temperature of the 

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