Partial Molar Enthalpy and Entropy Quiz

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An interactive step-by-step procedure requires the user to identify pure component and mixture enthalpies or entropies in a binary solution. The user determines the excess enthalpy or entropy (differences from an ideal solution). For enthalpies, the user then calculates the temperature change for adiabatic mixing. The partial molar enthalpies and entropies are determined from lines tangent to the enthalpy or entropy curves. Selecting "new problem" at any time resets to step 1 with different numerical values and either an enthalpy or entropy plot randomly selected.

Contributed by: Neil Hendren (February 2019)
With additional contributions by: John L. Falconer
(University of Colorado Boulder, Department of Chemical and Biological Engineering)
Open content licensed under CC BY-NC-SA


The molar enthalpy is given by:

, (1)

where and are the pure-component enthalpies (kJ/mol), and are the mole fractions of and and is a non-ideal parameter, which can be either a positive or negative value. The excess enthalpy is:

, (2)

where is the enthalpy of an ideal solution.

The change in temperature for adiabatic mixing is a function of the excess enthalpy and the heat capacity of the solution ().

, (3)

where and represent the initial and final temperatures of the solution.

, (4)

. (5)

The molar entropy of an ideal solution is:

. (6)

The excess entropy can be derived from excess Gibbs energy of mixing and an interaction parameter for the two components .

, (7)

. (8)

The partial molar entropies can be found from interactions of a line tangent to the versus curve using equations analogous to equations (4) and (5).


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