Water vapor

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Water vapor or water vapour (see spelling differences), also aqueous vapor, is the gas phase of water. Water vapor is one state of water within the hydrosphere. Water vapor can be produced from the evaporation of boiling liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously generated by evaporation and removed by condensation. Water vapor is lighter than air and triggers convection currents that can lead to clouds. Water vapor is a potent greenhouse gas along with other gases such as carbon dioxide and methane.

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General properties of water vapor

Evaporation/sublimation

Whenever a water molecule leaves a surface, it is said to have evaporated. Each individual water molecule which transitions between a more associated (liquid) and a less associated (vapor/gas) state does so through the absorption or release of kinetic energy. The aggregate measurement of this kinetic energy transfer is defined as thermal energy and occurs only when there is differential in the temperature of the water molecules. Liquid water that becomes water vapor takes a parcel of heat with it, in a process called evaporative cooling.[2] The amount of water vapor in the air determines how fast each molecule will return back to the surface. When a net evaporation occurs, the body of water will undergo a net cooling directly related to the loss of water.

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