Partial Molar Enthalpy

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The molar enthalpy of a binary mixture (blue curve) of and is plotted as a function of the mole fraction of component . The end points of the molar enthalpy are the pure-component enthalpies and . The partial molar enthalpies and are obtained by drawing a tangent line (black, dashed) at the black point, which indicates the mole fraction of the solution. The intersections of this tangent with the -axis at and correspond to and , respectively. You can change the mole fraction of in the mixture and the non-ideal parameter, which represents deviation from an ideal solution, with sliders. For an ideal solution the non-ideal parameter is zero, and the enthalpy of the mixture is a linear function of the molar enthalpies of the pure components.

Contributed by: Simon M. Lane and Rachael L. Baumann (April 2014)
With additional contributions by: John L. Falconer and Nick Bongiardina
(University of Colorado Boulder, Department of Chemical and Biological Engineering)
Open content licensed under CC BY-NC-SA


The molar enthalpy is:


where is the enthalpy (kJ/mol), and are the compositions of and , and is a non-ideal parameter.

The partial molar enthalpy is represented by a line tangent to at composition of the mixture :

Where is the partial molar enthalpy of component and is the partial molar enthalpy of component . A screencast video at [1] shows how to use this Demonstration, and a screencast at [2] presents an example.


[1] Partial Molar Enthalpy.

[2] Partial Molar Properties: Binary Solutions [Video]. (Apr 5, 2012)


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