Water is a great example to demonstrate this phenomena, when freezing liquid water create ice, it release quite a lot energy. The released energy helps liquid water to become solid ice during the and it keeps at 0℃.Heat energy plays an important role in changing matter from one state to another. 

When thermal energy is applied on a matter, normally the temperature of the matter changes, but it stays constant during its phase change transition. The temperature remains the same because the energy is required to change the matter’s state. 

Latent heat is expressed as the amount of heat energy per mole or mass unit wanted for a phase change to occur.