Question

At what temperature does evaporation of a liquid take place?

Answer 1

Hint: There are mainly three states of matter namely, solid, liquid and gas. The process of solid becoming a liquid is melting, liquid to gas is evaporation or vaporisation and again the reverse process that is, gas to liquid is condensation and liquid to solid is solidification. There are special cases where a solid directly changes to gas without entering liquid phase is known as sublimation and the gas directly changes to solid without entering the liquid phase is known as deposition.

Complete answer:
Definition: Evaporation is the process by which a liquid changes into a gas or vapour phase.
Example-melting of an ice cube, drying of wet floors and wet clothes.
Principle: The evaporation process is a surface phenomenon.
The evaporation to occur, there is a need for energy(heat). Energy is used to break the bonds that hold the molecules together which induces the evaporation. Evaporation takes place at all temperatures as the air molecules that strike the surface impart some energy to the molecules. But at higher temperatures the evaporation is more since the kinetic energy of a molecule is proportional to its temperature. So, generally at that boiling point the water easily evaporates.
Evaporation process causes a cooling effect. This is because as the liquid bond breaks, they evaporate becoming a gas causing the decrease in the average energy of the liquid and the liquid cools down. Hence evaporation causes cooling.
Example-after sweating ,the sweat gets evaporated from the excess heat of the body in turn causing the body to cool down.

Note:
The evaporation rates are higher at higher temperatures because as temperature increases, the amount of energy necessary for evaporation decreases. The rate of evaporation depends on vapour pressure, boiling point, specific heat, temperature and surface area. Application of evaporation is to separate the components of a homogeneous solid-liquid mixture in which the solid is recovered.
Example-extraction of salt from sea water.