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Accuracy of models that predict global warming: fix disambig

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'''Latent heat''' is the energy released or absorbed by a body or a [[thermodynamic system]] during a constant-temperature process. A typical example is a change of [[state of matter]], meaning a [[phase transition]] such as the melting of ice or the boiling of water.<ref name=Perrot>{{cite book
|author=Perrot, Pierre
|title=A to Z of Thermodynamics
|publisher=Oxford University Press
|year=1998
|isbn=0-19-856552-6
}}</ref><ref name=":0">{{cite book
|author=Clark, John, O.E.
|title=The Essential Dictionary of Science
|publisher=Barnes & Noble Books
|year=2004
|isbn=0-7607-4616-8
}}</ref> The term was introduced around 1762 by [[Scotland|Scottish]] chemist [[Joseph Black]]. It is derived from the Latin ''latere'' (''to lie hidden''). Black used the term in the context of [[calorimetry]] when referring to the heat transferred that caused a change of volume while the thermodynamic system was held at constant temperature.

In contrast to latent heat, an energy is called a [[sensible heat|sensible energy or heat]] when it causes processes that do result in a change of the temperature of the system.

{{Thermodynamics}}

==Usage==
Two of the more common forms of latent heat (or enthalpies or energies) encountered are [[enthalpy of fusion|latent heat of fusion]] ([[melting]]) and [[enthalpy of vaporization|latent heat of vaporization]] ([[boiling]]). These names describe the direction of energy flow when changing from one phase to the next: from solid to liquid, and liquid to gas.

In both cases the change is [[endothermic]], meaning that the system absorbs energy on going from solid to liquid to gas. The change is [[exothermic]] (the process releases energy) for the opposite direction. For example, in the [[Earth's atmosphere|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 less [[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 (matter)|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.

The terms ''sensible heat'' and ''latent heat'' are not special forms of energy; instead they characterize the same form of energy, [[heat]], in terms of their effect on a material or a thermodynamic system. A good way to remember the distinction is that a change in ''sensible heat'' may be ″sensed″ with a thermometer, and a change in ''latent heat'' is invisible to a thermometer – the temperature reading doesn't change. Heat is [[thermal energy]] in the process of transfer between a system and its surroundings or between two systems with a different temperature.

Both sensible and latent heats are observed in many processes while transporting energy in nature. Latent heat is associated with the phase changes of atmospheric water vapor, mostly [[vaporization]] and [[condensation]], whereas sensible heat is energy transferred that affects the temperature of the atmosphere.

The original usage of the term, as introduced by Black, was applied to systems that were intentionally held at constant temperature. Such usage referred to ''latent heat of expansion'' and several other related latent heats. These latent heats are defined independently of the conceptual framework of thermodynamics.<ref>Bryan, G.H. (1907). ''Thermodynamics. An Introductory Treatise dealing mainly with First Principles and their Direct Applications'', B.G. Tuebner, Leipzig, pages 9, 20–22.</ref>

When a body is heated at constant temperature by thermal radiation in a microwave field for example, it may expand by an amount described by its ''latent heat with respect to volume'' or ''latent heat of expansion'', or increase its pressure by an amount described by its ''latent heat with respect to pressure''.<ref>Maxwell, J.C. (1872). ''Theory of Heat'', third edition, Longmans, Green, and Co., London, page 73.</ref>

===Meteorology===
In meteorology, latent heat flux is the [[flux]] of heat from the Earth's surface to the [[Earth's atmosphere|atmosphere]] that is associated with [[evaporation]] or [[transpiration]] of water at the surface and subsequent [[condensation]] of [[water vapor]] in the [[troposphere]]. It is an important component of Earth's surface energy budget. Latent heat flux has been commonly measured with the [[Bowen ratio]] technique, or more recently since the mid-1900s by the [[eddy covariance]] method.

==History==
The English word ''[[wikt:latent#English|latent]]'' comes from Latin ''[[wikt:latens#Latin|latēns]]'', meaning ''lying hidden''.<ref>{{OEtymD|latent}}</ref><ref>Lewis, Charlton T. (1890). ''An Elementary Latin Dictionary''. Entry for [http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0060%3Aentry%3Dlatens latens].</ref> The term ''latent heat'' was introduced into calorimetry around 1750 when [[Joseph Black]], commissioned by producers of [[Scotch whisky]] in search of ideal quantities of fuel and water for their distilling process,<ref>{{Cite episode | title = Credit Where It's Due | url = | accessdate = | series = The Day the Universe Changed | serieslink = The Day the Universe Changed | credits = [[James Burke (science historian)|James Burke]] | network = BBC | date = 1979 | number = 6 | minutes =34 | time =50 | transcript = | transcripturl = | quote = | language = English}}</ref> to studying system changes, such as of volume and pressure, when the thermodynamic system was held at constant temperature in a thermal bath. [[James Prescott Joule]] characterised latent energy as the energy of interaction in a given configuration of particles, i.e. a form of [[potential energy]], and the sensible heat as an energy that was indicated by the thermometer,<ref>{{cite
|author=J. P. Joule
|title=The Scientific Paper of James Prescott Joule
|year=1884
|publisher=The Physical Society of London
|page=274
|quote=I am inclined to believe that both of these hypotheses will be found to hold good,—that in some instances, particularly in the case of sensible heat, or such as is indicated by the thermometer, heat will be found to consist in the living force of the particles of the bodies in which it is induced; whilst in others, particularly in the case of latent heat, the phenomena are produced by the separation of particle from particle, so as to cause them to attract one another
through a greater space.
}}, Lecture on Matter, Living Force, and Heat. May 5 and 12, 1847</ref> relating the latter to [[thermal energy]].

==Specific latent heat==
A ''specific'' latent heat (''L'') expresses the amount of energy in the form of heat (''Q'') required to completely effect a phase change of a unit of mass (''m''), usually {{gaps|1|kg}}, of a substance as an [[intensive property]]:
:<math>L = \frac {Q}{m}.</math>
Intensive properties are material characteristics and are not dependent on the size or extent of the sample. Commonly quoted and tabulated in the literature are the specific latent heat of fusion and the specific latent heat of vaporization for many substances.

From this definition, the latent heat for a given mass of a substance is calculated by
:<math>Q = {m} {L}</math>
where:
:''Q'' is the amount of energy released or absorbed during the change of phase of the substance (in [[kilojoule|kJ]] or in [[BTU]]),
:''m'' is the mass of the substance (in [[kg]] or in [[Pound (mass)|lb]]), and
:''L'' is the specific latent heat for a particular substance (kJ-kgm−1 or in BTU-lbm−1), either ''L''f for fusion, or ''L''v for vaporization.

==Table of latent heats==
The following table shows the latent heats and change of phase temperatures of some common fluids and gases.{{citation needed|date=June 2012}}
{| class="wikitable sortable"
|-
! scope="col" | Substance
! scope="col" | Latent Heat Fusion kJ/kg
! scope="col" | Melting Point °C
! scope="col" | Latent Heat Vaporization kJ/kg
! scope="col" | Boiling Point °C
|-
|[[Ethanol|Alcohol, ethyl]]
|108
| −114
|855
|78.3
|-
|[[Ammonia]]
|339
| −75
|1369
| −33.34
|-
|[[Carbon dioxide]]
|184
| −78
|574
| −57
|-
|[[Helium]]
| 
| 
|21
| −268.93
|-
|[[Hydrogen]](2)
|58
| −259
|455
| −253
|-
|[[Lead]]<ref>Yaws' Handbook of Properties of the Chemical Elements 2011 Knovel</ref>
|23.0
|327.5
|871
|1750
|-
|[[Nitrogen]]
|25.7
| −210
|200
| −196
|-
|[[Oxygen]]
|13.9
| −219
|213
| −183
|-
|[[R134a]]
| 
| −101
|215.9
| −26.6
|-
|[[1,1-Difluoroethane|R152a]]
| 
| −116
|326.5
|11.3
|-
|[[Toluene]]
|72.1
| −93
|351
|110.6
|-
|[[Turpentine]]
| 
| 
|293
| 
|-
|[[Water]]
|334
|0
|2260
|100
|-
|}

==Latent heat for condensation of water==
The latent heat of condensation of water in the temperature range from −25 °C to 40 °C is approximated by the following empirical cubic function:
:<math>L_\text{water}(T) = (2500.8 - 2.36 T + 0.0016 T^2 - 0.00006 T^3)~\text{J/g},</math><ref name="RYfit">[[Curve fitting#Fitting lines and polynomial curves to data points|Polynomial curve fit]]s to Table 2.1. {{cite book |author=R. R. Rogers & M. K. Yau |title=A Short Course in Cloud Physics |edition=3rd |year=1989 |publisher=Pergamon Press |isbn=0-7506-3215-1 |page=16}}</ref>
where the temperature <math>T</math> is taken to be the numerical value in °C.

For [[sublimation (phase transition)|sublimation]] and [[deposition (physics)|deposition]] from and into ice, the latent heat is almost constant in the temperature range from −40 °C to 0 °C and can be approximated by the following empirical quadratic function:
:<math>L_\text{ice}(T) = (2834.1 - 0.29 T - 0.004 T^2)~\text{J/g}.</math><ref name="RYfit"/>

==See also==
*[[Bowen ratio]]
*[[Eddy covariance]] flux (eddy correlation, eddy flux)
*[[Sublimation (physics)]]
*[[Specific heat capacity]]
*[[Enthalpy of fusion]]
*[[Enthalpy of vaporization]]

==References==
{{reflist|2}}

{{States of matter}}

[[Category:Thermochemistry]]
[[Category:Atmospheric thermodynamics]]
[[Category:Thermodynamics]]

General Circulation Model - Revision history

en>Jinkinson: /* Accuracy of models that predict global warming */ fix disambig

en>Gaba p: Undid revision 593508650 by Gaba p (talk)self rv, wrong button