Deviations from Ideality in Terms of Excess Thermodynamic Functions

Therefore the state in which the solute has a partial molar Gibbs function of p.2 can be found from the following limit, because 72 approaches unity as m2 approaches zero  

With this method of formulation, it also is possible to show that frequently a real solution at some molality exists for which p2 = that H 2 corresponds to // ,2 for a real solution at infinite dilution, and that 5 2 equals 5 ,2 for a real solution at a molality m2, which is neither zero nor m2j. 

7 DEVIATIONS FROM IDEALITY IN TERMS OF EXCESS THERMODYNAMIC FUNCTIONS 

Various functions have been used to express the deviation of observed behavior of solutions from that expected for ideal systems. Some functions, such as the activity coefficient, are most convenient for measuring deviations from ideality for a particular component of a solution. However, the most convenient measure for the solution as a whole, especially for mixtures of nonelectrolytes, is the series of excess functions (1) (3), which are defined in the foUowing way. 

We have derived an expression for the free energy of mixing two pure substances to form one mole of an ideal solution [Equation (14.35)], 

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