Gas - Definition and Overview

For other meanings see gas (disambiguation).

A gas is one of the phases of matter. Gases are, like liquids, fluids: they have the ability to flow and do not resist deformation. Unlike liquids, however, unconstrained gases do not occupy a fixed volume, but instead expand to fill whatever space they occupy. The kinetic energy in a gas is the second greatest of the states of matter (after plasma). Because of this increased kinetic energy, gas atoms and molecules tend to bounce off of one another, more so as the kinetic energy is increased.

The word "gas" was probably made by a Flemish chemist as a re-spelling of his pronunciation of the Greek word chaos.

See also

• Ideal gas
• Kinetic theory of gases