Molar enthalpy boiling point elevation

However, it must be borne in mind that the activity coefficients depend on temperature and pressure, as well as on composition, as discussed in the last section. Therefore a determination of the activity coefficient of the solvent in a particular solution by measurement of its freezing-point depression could not be used for the purpose of an accurate calculation of the boiling-point elevation of the same solution, without an additional knowledge of the enthalpies which appear in equation (9 25). Over appreciable ranges of temperature, the temperature-dependence of the enthalpies themselves must be allowed for, this dependence being expressible in terms of molar and partial molar heat capacities. 

Thus the elevation of the boiling point, AZb, of a liquid (molar mass, Mm, boiling point, Tb and enthalpy of vaporisation, AvapH° at 1 bar pressure) caused by addition of zwSoiute can be calculated using equation (52.12). 

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