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The enthalpy of fusion is the amount of energy required to convert one mole of solid into liquid. For example, when melting 1 kg of ice (at 0 °C under a wide range of pressures ), 333.55 kJ of energy is absorbed with no temperature change. The heat of solidification (when a substance changes from liquid to solid) is equal and opposite.
The specific enthalpy of fusion (more commonly known as latent heat) of water is 333.55 kJ/kg at 0 °C: the same amount of energy is required to melt ice as to warm ice from −160 °C up to its melting point or to heat the same amount of water by about 80 °C. Of common substances, only that of ammonia is higher.
Latent heat is energy released or absorbed by a body or a thermodynamic system during a constant-temperature process. Two common forms of latent heat are latent heat of fusion and latent heat of vaporization . These names describe the direction of energy flow when changing from one phase to the next: from solid to liquid, and liquid to gas.
For a liquid–gas transition, is the specific latent heat (or specific enthalpy) of vaporization; for a solid–gas transition, is the specific latent heat of sublimation. If the latent heat is known, then knowledge of one point on the coexistence curve , for instance (1 bar, 373 K) for water, determines the rest of the curve.
Triple point. In the following table, material data are given with a pressure of 611.7 Pa (equivalent to 0.006117 bar). Up to a temperature of 0.01 °C, the triple point of water, water normally exists as ice, except for supercooled water, for which one data point is tabulated here.
Melting ice cubes illustrate the process of fusion. Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which increases the substance's temperature to the melting point.
The energy released upon freezing is a latent heat, and is known as the enthalpy of fusion and is exactly the same as the energy required to melt the same amount of the solid. Low-temperature helium is the only known exception to the general rule. [ 8 ]
Mass concentration, g/ (100 ml) at 15.56 °C. Density relative to 4 °C water. Density at 20 °C relative to 20 °C water. Density at 25 °C relative to 25 °C water. Freezing temperature, °C. 10 °C. 20 °C. 25 °C.