Question

Explain why evaporation leads to cooling of the liquid?

Answer 1

Hint: Find the changes which take place when liquid evaporates. Think about what happens to the molecules of a liquid during the process of evaporation and how the molecules of liquid get converted from liquid phase to gaseous phase.

Complete step by step solution:
- Evaporation is the process in which a compound or solution in the liquid phase is converted into a gaseous phase.
- Cooling of a liquid means that the liquid temperature decreases and the container having the liquid feels cool to touch.
- The process of evaporation requires heat energy to take place.
- In the liquid phase, molecules are held together by intermolecular forces of attraction like hydrogen bonding, dipole-dipole interaction, Van der waals’ forces of attraction, etc.
- For the evaporation process to take place, the molecules in the liquid phase need to break these intermolecular forces of attraction by absorbing heat energy.
- Therefore, the process of evaporation is a bond-breaking process (removal of intermolecular attraction forces) and thus, it is endothermic.
- In the endothermic process, energy is absorbed by the environment.
- When the molecules in liquid phase escape into gaseous phase, they take the absorbed energy with them which causes the cooling effect of the liquid.
- Hence it is justified that evaporation causes a cooling effect of the liquid.

Note: Remember evaporation is an endothermic process. In evaporation, molecules in liquid phase absorb energy from the environment and then break the intermolecular forces of attraction and escape into gaseous phase along with the absorbed energy. That’s why evaporation causes a cooling effect.