What is Evaporation?



The spontaneous escaping of molecules of a liquid from their surface at any temperature is called evaporation.

Evaporation Process:

Most common question in this regard is,

How does evaporation work?

All the liquid molecules do not contain the same kinetic energies. Speed of molecules depends upon kinetic energy. Molecules with high kinetic energy move faster & vice versa. The molecules which reach surface of the liquid due to high kinetic energy escapes in atmosphere through overcoming attractions with neighboring molecules. This spontaneous change of liquid into its vapour continues at all temperatures.

Evaporation Cause cooling effect:

When high kinetic energy molecules leave the liquid and low kinetic energy molecules are left behind, the average kinetic energy of liquid molecules falls and hence the temperature of the liquid falls and heat moves from the surroundings to the liquid and then the temperature of surroundings also fall.


Factors affecting evaporation:

Factors affecting the rate of evaporation are,

(i) Surface Area:

Since evaporation occurs from liquid surface, so if surface area is increased then more molecules are able to escape and liquid evaporates more quickly.

(ii) Temperature:

For liquids having same surface area, the rate of evaporation is increased by the increasing temperature. At high temperature, the molecules having greater energy increase, and so rate of evaporation increases.

(iii) Intermolecular Forces:

Similarly, if intermolecular forces are weaker, the rate of evaporation is greater. For example, gasoline, whose molecules experience weaker London forces of attraction, evaporate much faster than water because of strong hydrogen bonding.

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