kinetic theory of gases


kinetic theory of gases
a theory that the particles in a gas move freely and rapidly along straight lines but often collide, resulting in variations in their velocity and direction. Pressure is interpreted as arising from the impacts of these particles with the walls of a container.
[1870-75]

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Theory based on a simple description of a gas, from which many properties of gases can be derived.

Established primarily by James Clerk Maxwell and Ludwig Boltzmann, the theory is one of the most important concepts in modern science. The simplest kinetic model is based on the assumptions that (1) a gas is composed of a large number of identical molecules moving in random directions, separated by distances that are large compared to their size; (2) the molecules undergo perfectly elastic (no energy loss) collisions with each other and with the walls of the container; and (3) the transfer of kinetic energy between molecules is heat. This model describes a perfect gas but is a reasonable approximation to a real gas. Using the kinetic theory, scientists can relate the independent motion of molecules of gases to their pressure, volume, temperature, viscosity, and heat conductivity.

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      a theory based on a simplified molecular or particle description of a gas, from which many gross properties of the gas can be derived.

      The British scientist James Clerk Maxwell and the Austrian physicist Ludwig Boltzmann, in the 19th century, led in establishing the theory, which became one of the most important concepts in modern science.

      The simplest kinetic model is based on the assumptions that: (1) the gas is composed of a large number of identical molecules moving in random directions, separated by distances that are large compared with their size; (2) the molecules undergo perfectly elastic collisions (no energy loss) with each other and with the walls of the container, but otherwise do not interact; and (3) the transfer of kinetic energy between molecules is heat. These simplifying assumptions bring the characteristics of gases within the range of mathematical treatment.

      Such a model describes a perfect gas (q.v.) and is a reasonable approximation to a real gas, particularly in the limit of extreme dilution and high temperature. Such a simplified description, however, is not sufficiently precise to account for the behaviour of gases at high densities.

      Based on the kinetic theory, pressure on the container walls can be quantitatively attributed to random collisions of molecules the average energy of which depends upon the gas temperature. The gas pressure can therefore be related directly to temperature and density. Many other gross properties of the gas can be derived, such as viscosity, thermal and electrical conduction, diffusion, heat capacity, and mobility. In order to explain observed deviations from perfect gas behaviour, such as condensation, the assumptions must be appropriately modified. In doing so, considerable insight has been gained as to the nature of molecular dynamics and interactions.

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Universalium. 2010.

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