Editing Vapor (section)

== Properties ==
[[Image:phase-diag2.svg|class=skin-invert-image|thumb|upright=1.3|The vapor-liquid critical point in a pressure-temperature [[phase diagram]] is at the high-temperature extreme of the liquid–gas phase boundary (the dotted green line gives the anomalous behaviour of water).]]
''Vapor'' refers to a gas phase at a temperature where the same substance can also exist in the [[liquid]] or [[solid]] state, below the [[critical temperature]] of the substance. (For example, water has a critical temperature of 374&nbsp;°C (647 K), which is the highest temperature at which liquid water can exist.) If the vapor is in contact with a liquid or solid phase, the two phases will be in a state of [[thermodynamic equilibrium|equilibrium]]. The term ''gas'' refers to a compressible fluid phase. Fixed gases are gases for which no liquid or solid can form at the temperature of the gas, such as air at typical ambient temperatures. A liquid or solid does not have to boil to release a vapor.

Vapor is responsible for the familiar processes of [[cloud]] formation and [[condensation]]. It is commonly employed to carry out the physical processes of [[distillation]] and [[headspace technology|headspace extraction]] from a liquid sample prior to [[gas chromatography]].

The constituent [[molecule]]s of a vapor possess vibrational, rotational, and translational motion. These motions are considered in the [[kinetic theory of gases]].