Enthalpy of fusion

The melting enthalpy ( heat of fusion also outdated ) refers to the energy required to melt a material sample of a solid at its melting point, that is, to transfer from the solid to the liquid state. Thereby bonding force between atoms or molecules can be overcome, without thereby increasing the kinetic energy and its temperature. The value of the enthalpy of fusion with the opposite sign is equal to the value of the enthalpy of solidification, which is released when a liquid to the solid state.

Quantities and units

The enthalpy of fusion is an energy. In the International System Size ( ISQ ), it therefore has the dimension

And thus in the International System of Units (SI), the coherent derived SI unit joule:

As a material constant is obtained, the specific enthalpy of fusion of a substance by the heat of fusion is related to the mass of the substance:

It is accordingly given in units of joules per kilogram:

In chemistry, the molar enthalpy of fusion is commonly used instead. They are obtained by the fusion is based on the amount of the substance:

The unit thus is joules per mole:

To obtain manageable numerical values ​​for typical fabrics, the values ​​of the molar heat of fusion is not normally expressed in Joule per mole of ( J / mol), but in kilojoules per mole ( kJ / mol). However, this unit is not coherent.

The specific enthalpy of fusion and the molar enthalpy of fusion can be converted by using the molar mass of the substance under consideration into one another:

Recommended by the IUPAC for the molar enthalpy of fusion size designation is different.

The index is derived from enthalpy of fusion, the English term for the enthalpy of fusion.

Values

The heat of fusion is a special case of latent heat.