Vapor

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(Redirected from Vapour)

This article is about the chemical use, for computer usage see vaporware

Water vapor condensing over a cup of hot tea

Vapor or vapour (see spelling differences) is some matter in gaseous state, while being normally a solid or liquid at room temperature.

Although vapor and gas are frequently (incorrectly) used interchangeably, vapor refers to a gas phase in a state of equilibrium with identical matter in a liquid or solid state below its boiling point, or at least capable of forming solid or liquid at the temperature of the vapor. The term gas refers to a compressible fluid phase, as in common usage. 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. The atmospheric boiling point of a liquid is the temperature at which the vapor pressure is equal to one atmosphere (unit). See the article on vapor pressure for more information on this topic.

The vapor pressure is the equilibrium pressure from a liquid (or solid) at a specific temperature. The vapor pressure of a liquid or solid (pure or a mixture) is not affected by the pressure in contact with the liquid or solid.

For two-phase systems (e.g., two liquid phases), the vapor pressure of the system is the sum of the vapor pressures of the two liquids. In the absence of stronger inter-species attractions between like-like or like-unlike molecules, the vapor pressure follows Raoult's Law, or the vapor pressure is equal to the sum of the product of the vapor pressure of the pure compound and its mole fraction in the mixture for all of the constituents.

The constituent atoms or molecules of a vapor possess vibrational, rotational, and translational motion. More information can be found under the entry of the Kinetic theory of gases.

[edit] Examples

Perfumes contain chemicals that vaporize at different temperatures. The top note vaporizes first followed by the heart note. The slowest to vaporize is the base note.

Fog, mist and haar are meteorological designations for visible near surface water vapour.

[edit] Trivia

Flammable liquids do not burn when ignited. It is the vapor cloud above the liquid that will burn if the vapor's concentration is between the lower explosive limit and upper explosive limit of the flammable liquid.