If a change of state happens: The energy needed for a substance to change state is called latent heat. When a change of state occurs, the energy supplied changes the energy stored (internal energy) but not the temperature. • The specific latent heat of a substance is the amount of energy required to change the state of one kilogram of the substance with no change in temperature. • energy for a change of state = mass × specific latent heat, E = m L • energy, E, in joules, J • mass, m, in kilograms, kg • specific latent heat, L, in joules per kilogram, J/kg • Specific latent heat of fusion – change of state from solid to liquid • Specific latent heat of vaporisation – change of state from liquid to vapour.