Latent Heat

Summary

All phase changes …
- take place at a specific temperature.
- take place without a change in temperature. (There is no temperature change during a phase change.)
- involve changes in internal potential energy.
- release or absorb latent heat.
  - Endothermic phase changes absorb heat from the environment. (They are cooling processes.)
  - Exothermic phase changes release heat to the environment. (They are warming processes.)
The specific latent heat (L) of a material …
- is a measure of the heat energy (Q) per mass (m) released or absorbed during a phase change.
- is defined through the formula Q = mL.
- is often just called the "latent heat" of the material.
- uses the SI unit joule per kilogram [J/kg].
There are three basic types of latent heat each associated with a different pair of phases.

	solid-liquid	liquid-gas	solid-gas
latent heat of …	fusion	vaporization	sublimation
endothermic phase changes	melting, liquefaction*	boiling, evaporation, vaporization	sublimation
exothermic phase changes	crystallization, freezing, fusion, solidification	condensation, liquefaction*	deposition
temperature	melting point, freezing point	boiling point, dew point	sublimation point, frost point
* Use of the word liquefaction should be avoided since the starting phase is ambiguous.