<P> For example, water has a critical temperature of 647 K (374 ° C; 705 ° F), which is the highest temperature at which liquid water can exist . In the atmosphere at ordinary temperatures, therefore, gaseous water (known as water vapor) will condense into a liquid if its partial pressure is increased sufficiently . </P> <P> A vapor may co-exist with a liquid (or a solid). When this is true, the two phases will be in equilibrium, and the gas - partial pressure will be equal to the equilibrium vapor pressure of the liquid (or solid). </P> <P> 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 ° 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 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 . </P> <P> 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 extraction from a liquid sample prior to gas chromatography . </P>

When should the term vapor be used instead of gas
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