Question

breifly explain why a substance expansd on heating

Answer 1

We know that molecules in every substance are in constant random motions and the vigorousness of the motion depends upon their thermal energies which is on account of the temperature. The vigorousness also determines the net intermolecular spacing in a substance and thus, in short, temperature determines the intermolecular spacing in a substance and thus causes expansion and contraction in it.

Now,

Objects expands on heating because the intermolecular spaces are increased by applying heat energy to them. They contract on cooling as we are removing the heat energy from them.