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Van der Waals forcesZoomA-Z

Subject - General Chemistry

The model of an ideal gas is based on the assumption that the particles do not have any volume of their own and do not interact with each other. At low density of the particles (low pressure), the medium distance between them is very large and correspondingly the sum of interactive energies in the ensemble is low. At high temperatures (high kinetic energies of the particles), attractive interactions can be neglected because the particles could leave the potential well due to high kinetic energies.

In a narrow sense, Van der Waals forces named after Johannes Diderik van der Waals are intermolecular attractive forces the energies of which decrease proportional to the molecular distance at the power of six. In the Van der Waals equation of state for real gases, these attractive forces are responsible for the so-called internal pressure a/V2.

Frequently, the concept is being used in a broader sense as a synonym for all weak intermolecular forces, such as the dispersion forces (London forces) representing the electrostatic attractive forces between permanent dipole moments, e.g. the quadrupolar moment and the Debye forces (attractive forces between permanent electrical moments and dipole moments caused by the former).