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Evaporation and condensation

“Evaporation is the changing of a liquid into vapours (gaseous state) from the surface of the liquid without heating it.”

Take some water in a dish.The water in the dish will disappear after some time.It is because the the molecules of water are in constant motion and possess kinetic energy.Fast moving molecules escape out from the surface of water and goes into the atmosphere.This is called evaporation.

Unlike boiling,evaporation takes place at all temperature but only from the surface of a liquid.The process of boiling takes at a certain fixed temperature which is the boiling  point of that liquid.At boiling point,a liquid is changing into vapours not only from surface but also within the liquid.These vapours come out of the boiling liquid as bubbles which breakdown on reaching the surface.

Factors effect evaporation:

  • Temperature:

At higher temperature,more molecules of a liquid are moving with high velocities.Thus,more molecules escape from its surface.Thus ,evaporation is faster at high temperature than at low temperature.

  • Surface area:

Larger is the area of a liquid ,greater number of molecules has the chance to escape from its surface.Therefore there will be more evaporation at sea than river and small reservoirs of water.

  • Wind:

Wind blowing over the surface of a liquid sweeps away the liquid molecules that have just escaped out.This increases the chance for more liquid molecules to escape out.

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