(a) From an atomic point of view, why do you have to heat a solid to melt it? (b) If you have a solid and a liquid at room temperature, what conclusion can you draw about the relative strengths of their inter-atomic forces?

A. & B. Heat energy is needed to convert solid into a liquid because heat energy increases the kinetic energy of the particles. The heat energy that it used to change 1 kg of solid into liquid at atmospheric pressure and at its melting point is called the latent heat of fusion.