Question

Give an example to explain that evaporation is a cooling process.

Answer 1

Hint:The process by which liquid changes to gas on heating is called evaporation. The liquid molecules acquire energy from the substance as well as its surroundings to change into a gaseous state. This transfer of energy causes the substance to lose heat.

Complete step by step answer:
Liquid changes to gas on gaining heat energy during evaporation. As the process of evaporation requires heat energy, it takes this required heat from the substance thus causing a cooling effect on it. An example where evaporation causes a cooling effect is human perspiration. Our skin has pores through which liquid from our body is expelled. This liquid changes into water vapour. While changing into vapour state, the liquid takes away heat from our body and escapes as vapour. This loss of heat from our body allows it to cool down.
Additional information:
Since wind increases the rate of evaporation, we feel cool on a windy day. The liquid on our skin gets evaporated at a faster rate on a windy day.A very similar process is transpiration in plants. Plants lose water through stomata in their leaves. This water is evaporated and causes a cooling effect on plants.The opposite of evaporation is condensation. Here, gas changes to liquid on losing heat.

Note:We must remember that only when liquid molecules gain heat they change into gaseous state. When liquid molecules lose heat on cooling, they change into solid state. This process is called freezing.