Melting is a first phase transition, melting has enthalpy, entropy and volume increase.
Melting temperature is called melting point or melting temperature. The melting temperature of a small molecule crystal is very narrow (usually less than 1 ° C), and the polymer is not completely crystallized; its melting temperature is often a wide range (usually 10 ~ 20 ℃). At room temperature is a solid material to reach a certain temperature after melting, become liquid, known as the molten state. Also liquid, but at room temperature is not stable. The molten state is a term used in chemistry, which corresponds to the solid-liquid coexistence state during the melting process. Only the crystal in the melting point may be in solid-liquid coexistence.