Question

Describe how a substance undergoes phase changes on a molecular level

Answer 1

At molecular level the interaction between the molecule decreases or increases as the result of which distance between the molecules increases or decreases respectively.

For example - in case of melting of a solid , the molecules start moving away from each other as they gain energy. Similarly in case of condensation process the molecules present in vapour or gaseous phase starts to move towards each other by losing energy and ultimately transforms to liquid.

The transfer of energy takes generally in form of heat.