Latent heat describes the amount of energy in the form of heat that is required for a material to undergo a change of phase. Two latent heats are typically described. One is latent heat of melting, and the other is latent heat of evaporation.
They are so named as to describe the direction of heat flow from one phase to the next:
- solid —> liquid —> gas.
The energy change is endothermic when going from solid to liquid to gas, but, exothermic when going in the opposite direction.
Latent heats and change of phase temps of common fluids and gases
| Substance
| Latent Heat
Melting
J/g
| Melting
Temp
°C
| Latent Heat
Boiling
J/g
| Boiling
Temp
°C
|
| Alcohol, ethyl
| 108
| -114
| 855
| 78.3
|
| Ammonia
| 339
|
| 1369
|
|
| Carbon Dioxide
| 184
|
| 574
|
|
| Helium
|
|
| 21
|
|
| Hydrogen
| 58
| -259
| 455
| -253
|
| Nitrogen
| 25.7
| -210
| 200
| -196
|
| Oxygen
| 13.9
| -219
| 213
| -183
|
| Toluene
|
|
| 351
|
|
| Turpentine
|
|
| 293
|
|
| Water
| 335
| 0
| 2272
| 100
|
For example, in the atmosphere when a molecule of water evaporates off the surface of any body of water, heat is transported by the water molecule into a lower temperature air parcel that contains more water vapor than its surroundings. Because energy is needed to turn water into water vapor, water vapor is a way for a body to release energy. If the water vapor is returned to a liquid or solid phase (by condensation or sublimation), the stored energy is released as sensible heat onto the surface where condensation (or sublimation) has occurred.
See also
External link
