How does the (a) average kinetic energy (b) average potential energy of molecules of a substance change during its change in phase at a constant temperature, on heating?

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How does the (a) average kinetic energy (b) average potential energy of molecules of a substance change during its change in phase at a constant temperature, on heating?

Calorimetry | Class 10 | ICSE | Physics | Selina

How does the (a) average kinetic energy (b) average potential energy of molecules of a substance change during its change in phase at a constant temperature, on heating?

Solution:

(a) Molecules’ average kinetic energy remains constant.
(b) Molecules’ average potential energy rises.
Explanation: When a substance is heated to a constant temperature, i.e., during its phase change state, the heat given causes vibrating molecules to gain potential energy, allowing them to overcome the intermolecular force of attraction and move around freely. This indicates that the material has changed its shape.
However, this heat has no effect on the molecules’ kinetic energy. As a result, there is no temperature increase when a substance changes phase.
This heat is referred to as latent heat, and it is used to change the condition of materials without increasing the temperature.

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