Other ways to measure the imperfection of a solution

We have seen two equivalent methods to charaeterize the imperfection of a solution via the eoeffieienls of activity and the excess Gibbs energy. On rare occasions, we find other methods we will briefly describe two of them in this section. 

This method essentially appUes to solutions in whieh a distinetion is made between the solvent and solutes. When taking into aceount an impeifeetion, the following relation is written for a solvent [3.30] in plaee of the aetivity coefficient in the logarithm, we ean introduee a correetive term aeeording to the logarithm and write  

If we consider a dilute solution with only one solute 5 in the previous solvent, we can nse the following approximation  

This relation shows the equivalence between the coefficients of activity and osmotic coefficient methods to describe a real solution. 

If the solution is not dilute, the relation [3.97] is no longer vahd, but we can still express the activity in an equivalent way by writing  

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