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Heat of Fusion

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heat of fusion [′hēt əv ′fyü·zhən]
The increase in enthalpy accompanying the conversion of 1 mole, or a unit mass, of a solid to a liquid at its melting point at constant pressure and temperature. Also known as latent heat of fusion.

Heat of Fusion 

(or latent heat of fusion), the amount of heat that must be supplied to a substance in an equilibrium constant-pressure and constant-temperature process to convert the substance from the solid (crystalline) state to the liquid state. The same amount of heat is liberated when the substance crystallizes.

The heat of fusion is a special case of the heat of a first-order transition. For a given substance, the heat of fusion may be determined per unit mass or per mole. In the former case, the heat of fusion is measured in, for example, joules per kg (J/kg) or kilocalories

Table 1. Heat of fusion of several substances
Hydrogen ...............–259.113.8958,200
Nitrogen ...............–209.866.0925,500
Mercury ...............–38.892.8211,800
Ice ...............079.4333,000
Tin ...............231.914.460,300
Lead ...............327.45.8924,700
Copper ...............108348.9205,000
Iron ...............153965272,000

per kg (kcal/kg). In the latter case, the heat of fusion may be expressed in joules per mole. The term “molar heat of fusion” is sometimes applied to the heat of fusion per mole. Table 1 gives the values of the heat of fusion per kg Lf for several substances at atmospheric pressure (760 mm Hg, or 101,325 newtons per m2) and at the melting point tm.

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[FIGURE 3 OMITTED] Thermal Analysis A TA instruments DSC2010 was used to measure the enthalpy of fusion and the melting temperature of samples taken from selected positions through the wall thickness of the various pipes.


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