The evaporation is a progressive passage of the liquid state in a gas state. It is different from the boiling which is a fast transition. It is a change of state called Vaporisation.

When there exists a free volume above a liquid, a fraction of the molecules composing the liquid is in gas form. In balance, the quantity of matter in gas form defines the saturating Steam pressure, which depends on the Température.

When the pressure partial of the vapor is lower than the saturating Steam pressure and that this one is itself lower than the environmental pressure, part of the molecules pass from the liquid phase to the gas phase: it is evaporation.

evaporation can take place only when one is in the presence of a mixture of gas. When the vapor of the liquid is the only gas, one does not have evaporation but a boiling (one can also have a boiling in the presence of a mixture of gas).

Evaporation is an essential important phenomenon in the cycle of the life. The well-known cycle of water (liquid water becomes cloud, then falls down in rain or snow) requires this stage.

Evaporation requires a quantity of energy in general considerable (the Latent heat of vaporization), which allows for example the temperature control at the Homéotherme S by Transpiration and evaporation of the Sueur, or the cooling of a ground jug, or air by atomizing (Aérosol of Eau).

Associated words

See too

  • Driving with water

Simple: Evaporation

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