Question

Give reason:
The water kept in an earthen pot (matka) remains cool?

Answer 1

Hint: Earthen pot is made of mud. So, it contains mud particles due to which there are very tiny pores from where the process of evaporation takes place. This process produces a cooling effect. The evaporation takes place at the cost of heat generated in water. So, the water loses heat and remains cool.

Complete Step By Step Solution
Vaporization can change the state of matter from a solid or liquid to a gas. During evaporation, the liquid state of matter is turned directly into a gas. The process of evaporation takes place from the surface.
So, in earthen pots the evaporation takes place from the surface of the pots from the holes present due to its formation from mud. The latent heat required for vaporization is taken from the water kept inside the earthen pot. Therefore, the water loses its heat and remains cold even in the summer season.

Additional Information
Evaporation is the process by which an element undergoes transition from its liquid state to its gaseous state. The rate of evaporation depends on the temperature difference between the evaporating surface and the air, the relative humidity, and wind.
When a substance in liquid state is given energy, it changes its phase from liquid to vapor; the energy absorbed in this process is called Heat of vaporization. The heat of vaporization of water is about 2260 kJ/kg. The vaporization is the opposite process of condensation. When water evaporates, energy is required for the water molecules to overcome the forces of attraction between them. The transition in phase from water to vapor requires a certain amount of energy. This energy required for the transition is provided by the heat of the water kept inside the earthen pot.

Note
Latent heat of vaporization is a physical property of a substance. It is defined as the heat required in changing one mole of liquid at its boiling point under standard atmospheric pressure. The heat of vaporization decreases with the increase in temperature and it completely vanishes at a certain point which is known as the critical temperature.