Latent heat

Latent heat

In thermochemistry, latent heat is the amount of energy in the form of heat released or absorbed by a substance during a change of phase state(i.e. solid, liquid, or gas), &ndash; also called a phase transition.cite book | author=Perrot, Pierre | title=A to Z of Thermodynamics | publisher=Oxford University Press | year=1998 | id=ISBN 0-19-856552-6] [cite book | author=Clark, John, O.E.| title=The Essential Dictionary of Science | publisher=Barnes & Noble Books | year=2004 | id=ISBN 0-7607-4616-8]

The term was introduced around 1750 by Joseph Black as derived from the Latin "latere", to lie hidden. The term is now dated, replaced by "enthalpy of transformation".

Two latent heats (or enthalpies) are typically described: latent heat of fusion (melting), and latent heat of vaporization (boiling). The names describe the direction of heat flow from one phase to the next: solid → liquid → gas.

The change is endothermic, i.e. the system absorbs energy, when the change is from solid to liquid to gas. It is exothermic (the process releases energy) when it is in the opposite direction. For example, in the atmosphere, when a molecule of water evaporates from the surface of any body of water, "energy" 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 overcome the molecular forces of attraction between water particles, the process of transition from a parcel of water to a parcel of vapor requires the input of energy causing a drop in temperature in its surroundings. If the water vapor condenses back to a liquid or solid phase onto a surface, the latent energy absorbed during evaporation is released as sensible heat onto the surface. The large value of the enthalpy of condensation of water vapor is the reason that steam is a far more effective heating medium than boiling water, and is more hazardous.

Latent heat equation

The equation for latent heat is:

:$Q = mL ,$
where:

:"Q" is the amount of energy released or absorbed during the change of phase of the substance (in joules),
:"m" is the mass of the substance,
:"L" is the specific latent heat for a particular substance (J kg-1).

In other words, specific latent heat is found when energy is divided by mass.

Table of latent heats

References

ee also

*Heat of vaporization
*Heat of fusion
*Bowen ratio
*Sublimation (physics)
*Specific heat capacity

Wikimedia Foundation. 2010.

Look at other dictionaries:

• Latent heat — Latent La tent (l[=a] tent), a. [L. latens, entis, p. pr. of latere to lie hid or concealed; cf. Gr. lanqa nein, E. lethargy: cf. F. latent.] 1. Not visible or apparent; hidden; concealed; secret; dormant; as, latent springs of action. [1913… …   The Collaborative International Dictionary of English

• latent heat — n heat given off or absorbed in a process (as fusion or vaporization) other than a change of temperature * * * the amount of heat absorbed or given off by a body without changing temperature, as when it undergoes a change of state …   Medical dictionary

• latent heat — n. the heat liberated or absorbed by a substance as it changes phase at a constant temperature and pressure …   English World dictionary

• Latent heat — Latent heat. См. Скрытая теплота. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

• latent heat — Physics. heat absorbed or radiated during a change of phase at constant temperature and pressure. Cf. heat of fusion, heat of vaporization. [1750 60] * * * Characteristic amount of energy absorbed or released by a substance during a change in… …   Universalium

• latent heat —   release of heat during a change of state. Condensation of water releases latent heat to the atmosphere because it no longer needs the heat energy that was put in to change it from liquid to gas in the first place …   Geography glossary

• latent heat — fazinio virsmo šiluma statusas T sritis Standartizacija ir metrologija apibrėžtis Šilumos kiekis, kurio reikia medžiagai izoterminėmis sąlygomis iš vienos fazės virsti kita. atitikmenys: angl. heat of phase transformation; heat of phase… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

• latent heat — fazinio virsmo šiluma statusas T sritis chemija apibrėžtis Šilumos kiekis, kurio reikia medžiagai izoterminėmis sąlygomis iš vienos fazės pereiti į kitą. atitikmenys: angl. heat of phase transformation; heat of phase transition; latent heat rus.… …   Chemijos terminų aiškinamasis žodynas

• latent heat — slaptoji šiluma statusas T sritis fizika atitikmenys: angl. latent heat vok. latente Wärme, f rus. скрытая теплота, f pranc. chaleur latente, f …   Fizikos terminų žodynas

• Latent heat flux — is the flux of heat from the Earth s surface to the atmosphere that is associated with evaporation of water at the surface and subsequent condensation of water vapor in the troposphere. It is an important component of Earth s surface energy… …   Wikipedia