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Water vapor, water vapour or aqueous vapor is the gaseous phase of water. It is one state of water within the hydrosphere . Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice .
The vapor pressure of water is the pressure exerted by molecules of water vapor in gaseous form (whether pure or in a mixture with other gases such as air). The saturation vapor pressure is the pressure at which water vapor is in thermodynamic equilibrium with its condensed state .
Part of the pure rotation absorption spectrum of water vapour Rotating water molecule. The water molecule is an asymmetric top, that is, it has three independent moments of inertia. Rotation about the 2-fold symmetry axis is illustrated at the left.
Water vapor, the gaseous state of water, is generally invisible to the human eye. [2] Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depends on the temperature and pressure of the system of interest. The same amount of water vapor results in higher relative humidity in cool air than warm air.
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). 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 ...
Water moves perpetually through each of these regions in the water cycle consisting of the following transfer processes: evaporation from oceans and other water bodies into the air and transpiration from land plants and animals into the air. precipitation, from water vapor condensing from the air and falling to the earth or ocean.
The water in food has a tendency to evaporate, but the water vapor in the surrounding air has a tendency to condense into the food. When the two tendencies are in balance— and the air and food are stable—the air's relative humidity (expressed as a fraction instead of as a percentage) is taken to be the water activity, a w .
The solid/liquid/vapor triple point of liquid water, ice I h and water vapor in the lower left portion of a water phase diagram. The temperature and pressure at which ordinary solid, liquid, and gaseous water coexist in equilibrium is a triple point of water.