Bachier En Ciencias Y Letras

Evaporation
From Wikipedia, the free encyclopedia
Jump to: navigation, search
|[pic] |This article is in need of attention from an expert on the subject. WikiProject Physics or the Physics Portal may be able to |
| |help recruit one. (November 2008) |


[pic]
[pic]
Water vapor thathas evaporated and disappeared from hot tea condenses into visible droplets. Gaseous water is invisible, but the clouds of water droplets are evidence of evaporation followed by condensation.
Evaporation is a type of vaporization of a liquid, that occur only on the surface of a liquid. The other type of vaporization is boiling, that instead occurs on the entire mass of the liquid.
Evaporationis a type of phase transition; it is the process by which molecules in a liquid state (e.g. water) spontaneously become gaseous (e.g. water vapor). Generally, evaporation can be seen by the gradual disappearance of a liquid from a substance when exposed to a significant volume of gas. Vaporization and evaporation however, are not entirely the same processes.[citation needed]
On average, themolecules in a glass of water do not have enough heat energy to escape from the liquid, or else the liquid would turn into vapor quickly (see boiling point). When the molecules collide, they transfer energy to each other in varying degrees, based on how they collide. Sometimes the transfer is so one-sided for a molecule near the surface that it ends up with enough energy to escape.
Liquids that do notevaporate visibly at a given temperature in a given gas (e.g. cooking oil at room temperature) have molecules that do not tend to transfer energy to each other in a pattern sufficient to frequently give a molecule the heat energy necessary to turn into vapor. However, these liquids are evaporating, it's just that the process is much slower and thus significantly less visible.
Evaporation is anessential part of the water cycle. Solar energy drives evaporation of water from oceans, lakes, moisture in the soil, and other sources of water. In hydrology, evaporation and transpiration (which involves evaporation within plant stomata) are collectively termed evapotranspiration. Evaporation is caused when water is exposed to air and the liquid molecules turn into water vapor which rises up andforms clouds.
|Contents |
|[hide] |
|1 Theory |
|1.1 Evaporative equilibrium |
|2 Factors influencing the rate of evaporation|
|3 Applications |
|3.1 Combustion vaporization |
|3.2 Film deposition |
|4 See also |
|5 References|
|6 External links |


[pic][edit] Theory
See also: Kinetic theory

For molecules of a liquid to evaporate, they must be located near the surface, be moving in the proper direction, and have sufficient kinetic energy to overcome liquid-phase intermolecular forces.[1] Only asmall proportion of the molecules meet these criteria, so the rate of evaporation is limited. Since the kinetic energy of a molecule is proportional to its temperature, evaporation proceeds more quickly at higher temperatures. As the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid thus decreases. This phenomenon is also...