Intermolecular potential energy depends on the magnitude of the intermolecular forces and the position the molecules have relative to each other at any instant of time. It is impossible to determine accurately the magnitude of this energy because either the exact configuration and orientation of the molecules at any time or the exact intermolecular potential function is not known. However, there are two situations for which good approximations can be made. The first situation is at low or moderate densities. In this case the molecules are relatively widely spaced, so that only two-molecule or two- and three-molecule interactions contribute to the potential energy. At these low and moderate densities, techniques are available for determining, with reasonable accuracy, the potential energy of a system composed of reasonably simple molecules. The second situation is at very low densities; under these conditions the average intermolecular distance between molecules is so large that the potential energy may be assumed to be zero. Consequently, in this case a system of independent particles (an ideal gas) can be obtained and, therefore, from a statistical point of view, efforts can be concentrated on evaluating the molecular translational and internal energies.
Related ▪ L - Intermolecular Forces
▪ L - Intramolecular Energy