Question

why is heat energy needed to melt a solid ? what is this heat energy called?

Answer 1

Heat energy supplied to a solid increases if d current temp. is less than its melting point....
When the temperature reaches the melting point, the solid absorbs the energy and increases its internal energy which tends to break the bonds between the molecules and makes them move more easily..
This heat energy is knwn as "Latent heat energy"..

Answer 2

Explanation:

It is known that molecules of a solid are closely held together. Therefore, force of attraction between the molecules of a solid is very strong.

When we provide heat to a solid then its molecules start to vibrate. As a result, bond between the molecules break and thus, force of attraction decreases.

Hence, solid changes into liquid.

When without any change in temperature a solid changes into liquid then the heat required for this conversion is known as latent heat.