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.
Contributed by: Megan E. Maguire and Rachael L. Baumann (December 2013)
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 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  shows how to use this Demonstration.
 Three Intermolecular Potential Models. www.colorado.edu/learncheme/thermodynamics/ThreeIntermolecularPotentialModels.html.