Real Gases

Authored by: Igor Bello

Vacuum and Ultravacuum

Print publication date:  November  2017
Online publication date:  November  2017

Print ISBN: 9781498782043
eBook ISBN: 9781315155364
Adobe ISBN:


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At vacuum conditions, the real volume of molecules is a small fraction of the geometrical volume in which the molecules are located, and the average intermolecular distances are considerably larger than those of the molecules themselves. Molecules are therefore presumed to be mass points among which no interactive forces exist. In these conditions, gases behave as ideal and satisfy the ideal gas laws. However, at higher pressure, the volume of actual molecules cannot be neglected any further and the shorter intermolecular distances (fewer molecular diameters) among neighboring molecules invoke intermolecular forces. Consequently, the gas behaviors deviate from those of ideal gases. The difference between individual gases becomes more significant with an increase in the gas pressure. The simplest case of molecular interactive forces can be illustrated with examples of idealized single atomic molecules, such as neon or argon, which do not exhibit electric dipoles and can be treated as spherical particles.

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