vapour

physics

Also known as: vapor

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July 14, 2026

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In physics, a vapor is a substance in its gaseous phase. Vaporization is the process by which a liquid or solid transforms into this gaseous state. This conversion requires heat to overcome the cohesive forces holding the substance together in its liquid or solid form.1

Vaporization can occur through boiling, where vapor bubbles form within a liquid, or through sublimation, which is the direct conversion of a solid to vapor. The reverse process, condensation, occurs when vapor returns to a liquid or solid state, releasing heat. Water vapor plays a crucial role in Earth's radiation balance and is a key component of the water cycle, though it constitutes a small fraction of the hydrosphere. The kinetic theory of gases describes the behavior of gases based on molecular motion and collisions.123

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absolute humidity
vapour concentration or density in the air. If m_v is the mass of vapour in a volume of air, then absolute humidity, or d_v, is simply d_v = m_v/ V, in which V is the volume and d_v is expressed
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vapour concentration or density in the air. If m_v is the mass of vapour in a volume of air, then absolute humidity, or d_v, is simply d_v = m_v/ V, in which V is the volume and d_v is expressed
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separation and purification
Distillation
…a definite amount of its vapor is present. The concentration of the vapor and, therefore, the pressure that it exerts increase as the temperature is raised. When the pressure of the vapor equals the pressure of the surroundings (one atmosphere in an open vessel at sea level), the substance boils:…
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…a definite amount of its vapor is present. The concentration of the vapor and, therefore, the pressure that it exerts increase as the temperature is raised. When the pressure of the vapor equals the pressure of the surroundings (one atmosphere in an open vessel at sea level), the substance boils:…
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crystal
Vapour growth
Crystals can be grown from a vapour when the molecules of the gas attach themselves to a surface and move into the crystal arrangement. Several important conditions must be met for this to occur. At constant temperature and equilibrium conditions, the average number…
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Crystals can be grown from a vapour when the molecules of the gas attach themselves to a surface and move into the crystal arrangement. Several important conditions must be met for this to occur. At constant temperature and equilibrium conditions, the average number…
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chromatography
Gas chromatographic detectors
…chromatographic detectors sense the solute vapours in the mobile phase as they emerge from the column. Thermal-conductivity detectors compare the heat-conducting ability of the exit gas stream to that of a reference stream of pure carrier gas. To accomplish this, the gas streams are passed over heated filaments in thermal-conductivity…
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…chromatographic detectors sense the solute vapours in the mobile phase as they emerge from the column. Thermal-conductivity detectors compare the heat-conducting ability of the exit gas stream to that of a reference stream of pure carrier gas. To accomplish this, the gas streams are passed over heated filaments in thermal-conductivity…
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saturation
…and the state of a vapour similarly left in contact with the pure solid or liquid form of the substance. In the first example, the solution is saturated when the rate at which the pure substance dissolves in the solvent to enter the solution is exactly equal to the rate…
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…and the state of a vapour similarly left in contact with the pure solid or liquid form of the substance. In the first example, the solution is saturated when the rate at which the pure substance dissolves in the solvent to enter the solution is exactly equal to the rate…
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