In physics a vapor (American) or vapour (British) is a substance in the gas phase at a temperature lower than its critical temperature, which means that the vapor can be condensed to a liquid by increasing the pressure on it without reducing the temperature. A vapor is different from an aerosol. An aerosol is a suspension of tiny particles of liquid, solid, or both within a gas. 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. 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).
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.)
If the vapor pressure exceeds the equilibrium value, it becomes supersaturated and condenses on any available nucleation sites e. g. particles of dust. This principle is used in cloud chambers, where particles of radiation are visualized because they nucleate formation of water droplets.
The vapor pressure is the equilibrium pressure from a liquid or a solid at a specific temperature. The equilibrium vapor pressure of a liquid or solid is not affected by the amount of contact with the liquid or solid interface. The normal boiling point of a liquid is the temperature at which the vapor pressure is equal to normal atmospheric pressure. For two-phase systems (e.g., two liquid phases), the vapor pressure of the individual phases are equal. In the absence of stronger inter-species attractions between like-like or like-unlike molecules, the vapor pressure follows Raoult's law, which states that the partial pressure of each component is the product of the vapor pressure of the pure component and its mole fraction in the mixture. The total vapor pressure is the sum of the component partial pressures. Examples
Perfumes contain chemicals that vaporize at different temperatures and
at different rate in scent accords, known as notes.
Atmospheric water vapor is found near the earth's surface, and may
condense into small liquid droplets and form meteorological phenomena,
such as fog, mist, and haar.
Mercury-vapor lamps and sodium vapor lamps produce light from atoms in
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 flammable limit (LFL) and upper flammable limit
(UFL), of the flammable liquid.
Measuring vapor Since it is in the gas phase, the amount of vapor present is quantified by the partial pressure of the gas. Also, vapors obey the barometric formula in a gravitational field, just as conventional atmospheric gases do. See also
Look up vapor or vapour in Wiktionary, the free dictionary.
^ a b c R. H. Petrucci, W. S. Harwood, and F. G. Herring, General Chemistry, Prentice-Hall, 8th ed. 2002, p. 483–86. ^ a b c Cheng, T. (2014). "Chemical evaluation of electronic cigarettes". Tobacco Control. 23 (Supplement 2): ii11–ii17. doi:10.1136/tobaccocontrol-2013-051482. ISSN 0964-4563. PMC 3995255 . PMID 24732157. ^ Thomas Engel and Philip Reid, Physical Chemistry, Pearson Benjamin-Cummings, 2006, p.194 ^ Ferguson, Lon H.; Janicak, Dr Christopher A. (2005-09-01). Fundamentals of Fire Protection for the Safety Professional. Government Institutes. ISBN 9781591919605.
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States of matter (list)
Bose–Einstein condensate Fermionic condensate Degenerate matter Quantum Hall Rydberg matter Rydberg polaron Strange matter Superfluid Supersolid Photonic matter
QCD matter Lattice QCD Quark–gluon plasma Color-glass condensate Supercritical fluid
Antiferromagnet Ferrimagnet Ferromagnet
String-net liquid Superglass
Enthalpy of fusion Enthalpy of sublimation Enthalpy of vaporization Latent heat Latent internal energy Trouton's ratio Volatility
Binodal Compressed fluid Cooling curve Equation of state Leidenfrost effect Macroscopic quantum phenomena Mpemba effect Order and disorder (physics) Spinodal Superconductivity Superheated vapor Superheating Thermo-dielectric effect
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