Evaluation of relative partial molar enthalpies

Although it is not possible to determine absolute values of partial molar enthalpies, we can evaluate Ha and relative to appropriate solvent and solute reference states. 

The relative partial molar enthalpy of the solvent is defined by 

This is the partial molar enthalpy of the solvent in a solution of given composition relative to pure solvent at the same temperature and pressure. 

La can be related to molar differential and integral enthalpies of solution as follows. The enthalpy change to form a solution from amounts a and b of pure solvent and solute is given, from the additivity rule, by A//(sol) = (haHa + n H ) — (haH + We 

Equating both expressions for A//(sol), solving for La, and replacing n /tiA by MaWb, we obtain 

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