Three Intermolecular Potential Models

This Demonstration considers three models for intermolecular potentials: square-well, Sutherland, and Lennard-Jones. Potentials for molecule (blue), molecule (green), and an mixture (orange) are shown. Use a slider to vary the binary interaction parameter , which represents how non-ideal the mixture is ( for the ideal case). The attractive-strength ratio represents the relative well depths of to . The diameter ratio represents the relative sizes of the molecules. The relative width is the ratio of attractive diameter to the repulsive diameter.


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The square-well potential is:
The Sutherland potential is:
The Lennard–Jones potential is:
where is the intermolecular potential, is the distance between the molecule centers, is the molecular diameter, is the depth of the potential well, and is the well width for square-well potential.
The attractive strength parameter of the mixture is given by:
where is the binary interaction parameter, and and are the attractive strength parameters for molecules and .
A larger negative number for the binary interaction parameter represents stronger interactions between and relative to those between and or and . Analogously, a smaller positive number represents weaker interactions.
The molecular diameter parameter for the mixture is:
where and are the diameter parameters for molecules and .
A screencast video at [1] shows how to use this Demonstration.
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