Heat of melting
Melting heat, also known as melting heat, is the unit mass of material from solid to liquid, the body absorbs the heat. The temperature at which the object melts is called the melting point. Melting heat is a latent heat, in the process of melting, the material continues to absorb heat and temperature unchanged, it can not be directly detected by the temperature changes in the heat. Each substance has a different heat of fusion. Crystals have a fixed melting point at a certain pressure and also have a fixed heat of fusion; amorphous, such as glass and plastic, do not have a fixed melting point and therefore do not have a fixed heat of fusion. In the same substance, the liquid has a higher internal energy than the solid state, so that during the melting process, the solid matter absorbs heat to convert it into liquid. Likewise, when the material changes from liquid to solid, the same energy is released. Liquid particles in the liquid compared with the solid, received a smaller intermolecular force, and therefore have a higher internal energy. The value of the heat of fusion is, in most cases, greater than zero, indicating that the object absorbs heat upon melting, exotherm in solidification, and helium is the only exception. Helium-3 at a temperature of less than 0.3 Kelvin, the heat of fusion is less than zero. Helium-4 at a temperature of 0.