latent heat
| Dictionary: latent heat |
n.
The quantity of heat absorbed or released by a substance undergoing a change of state, such as ice changing to water or water to steam, at constant temperature and pressure. Also called heat of transformation.
| 5min Related Video: latent heat |
| Chemistry Dictionary: latent heat |
Symbol L. The quantity of heat absorbed or released when a substance changes its physical phase at constant temperature (e.g. from solid to liquid at the melting point or from liquid to gas at the boiling point). For example, the latent heat of vaporization is the energy a substance absorbs from its surroundings in order to overcome the attractive forces between its molecules as it changes from a liquid to a gas and in order to do work against the external atmosphere as it expands. In thermodynamic terms the latent heat is the enthalpy of evaporation (ΔH), i.e. L=ΔH=ΔU+pΔV, where ΔU is the change in the internal energy, p is the pressure, and ΔV is the change in volume.
The specific latent heat (symbol l) is the heat absorbed or released per unit mass of a substance in the course of its isothermal change of phase. The molar latent heat is the heat absorbed or released per unit amount of substance during an isothermal change of state.
| Britannica Concise Encyclopedia: latent heat |
For more information on latent heat, visit Britannica.com.
| Geography Dictionary: latent heat |
The quantity of heat absorbed or released when a substance changes its physical state at constant temperature, e.g. from a solid to a liquid at its melting point, or from a liquid to a gas at its boiling point. The release of latent heat of condensation in the rising air of a
| Architecture: latent heat |
The amount of heat which is absorbed or evolved in changing the state of a substance without changing its temperature, e.g., in freezing or vaporizing water.
| Columbia Encyclopedia: latent heat |
latent heat, heat change associated with a change of state or phase (see states of matter). Latent heat, also called heat of transformation, is the heat given up or absorbed by a unit mass of a substance as it changes from a solid to a liquid, from a liquid to a gas, or the reverse of either of these changes. It is called latent because it is not associated with a change in temperature. Each substance has a characteristic heat of fusion, associated with the solid-liquid transition, and a characteristic heat of vaporization, associated with the liquid-gas transition. The latent heat of fusion for ice is 80 calories per gram (see calorie). This amount of heat is absorbed by each gram of ice in melting or is given up by each gram of water in freezing. The latent heat of vaporization of steam is 540 calories per gram, absorbed during vaporization or given up during condensation. For a substance going directly from the solid to the gas state, or the reverse, the heat absorbed or given up is known as the latent heat of sublimation.
| Science Dictionary: latent heat |
The heat released or absorbed when matter undergoes a change of phase (see phases of matter). If the heat is given off during the change from a liquid to a solid, it is called heat of fusion. If it is given off during the change from a gas to a liquid, it is called heat of vaporization.
| Wikipedia: Latent heat |
The expression latent heat refers to the amount of energy released or absorbed by a chemical substance during a change of state that occurs without changing its temperature, meaning a phase transition such as the melting of ice or the boiling of water.[1][2] The term was introduced around 1750 by Joseph Black as derived from the Latin latere, to lie hidden.
Contents |
Usage
Two of the more common forms of latent heat (or enthalpies or energies) encountered are latent heat of fusion (melting) and latent heat of vaporization (boiling). These names describe the direction of energy flow when changing from one phase to the next: solid → liquid → 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 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.
Specific latent heat
The specific latent heat is the amount of energy required to convert 1 kg (or 1 lb) of a substance from solid to liquid (or vice-versa) without a change in the temperature of the surroundings -- all absorbed energy goes into the phase change -- is known as the specific latent heat of fusion. Likewise, the amount of energy required to convert 1 kg (or 1 lb) of a substance from liquid to gas (or vice-versa) without a change in the external temperature is known as the specific latent heat of vaporization for that substance. Tables of values for the two specific latent heats are published; values for some common substances are given below.
The latent heat for a different mass of the substance can be calculated using the equation:
- Q = mL
where:
- Q is the amount of energy released or absorbed during the change of phase of the substance (in kJ or in BTU),
- m is the mass of the substance (in kg or in lb), and
- L is the specific latent heat for a particular substance (kJ-kgm-1 or in BTU-lbm-1); substituted as Lf to represent as the specific latent heat of fusion, Lv as specific latent heat of vaporization.
In other words, specific latent heat is found when energy is divided by mass, or as represented as 
.
Table of latent heats
The following table shows the latent heats and change of phase temperatures of some common fluids and gases.
| Substance | Latent Heat Fusion kJ/kg |
Melting Point °C |
Latent Heat Vaporization kJ/kg |
Boiling Point °C |
|---|---|---|---|---|
| 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[3] | 24.5 | 372.3 | 871 | 1750 |
| Nitrogen | 25.7 | -210 | 200 | -196 |
| Oxygen | 13.9 | -219 | 213 | -183 |
| R134a | -101 | 215.9 | -26.6 | |
| Toluene | -93 | 351 | 110.6 | |
| Turpentine | 293 | |||
| Water | 334 | 0 | 2260 (at 100oC) | 100 |
Latent heat for water
To calculate the latent heat of condensation in water in the temperature range from −40 °C to 40 °C the following empirical cubic function can be used:
- Lwater(T) = − 0.0000614342T3 + 0.00158927T2 − 2.36418T + 2500.79[4]
with an determination coefficient of R2 = 0.999988
References
- ^ Perrot, Pierre (1998). A to Z of Thermodynamics. Oxford University Press. ISBN 0-19-856552-6.
- ^ Clark, John, O.E. (2004). The Essential Dictionary of Science. Barnes & Noble Books. ISBN 0-7607-4616-8.
- ^ Textbook: Young and Geller College Physics, 8e, Pearson Education
- ^ Cubic fit to Table 2.1,p.16, Textbook: R.R.Rogers & M.K. Yau, A Short Course in Cloud Physics, 3e,(1989), Pergamon press
See also
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Learn More
 | evaporation (physics) |
| Black, Joseph (British chemist) |
| decalescence (metallurgy) |
Help us answer these
 | What are the merits of specific latent heat? |
| What has the highest latent heat of fusion? |
| What is the latent heat of alcohol? |
Post a question - any question - to the WikiAnswers community:
Copyrights:
 |
 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more |
 |
| Chemistry Dictionary. A Dictionary of Chemistry. Sixth Edition. Copyright © Market House Books Ltd, 2008. All rights reserved. Read more |
 |
| Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved. Read more |
|
| Geography Dictionary. A Dictionary of Geography. Copyright © Susan Mayhew 1992, 1997, 2004. All rights reserved. Read more |
 |
| Architecture. McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc. All rights reserved. Read more |
 |
| Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/. Read more |
 |
| Science Dictionary. The New Dictionary of Cultural Literacy, Third Edition Edited by E.D. Hirsch, Jr., Joseph F. Kett, and James Trefil. Copyright © 2002 by Houghton Mifflin Company. Published by Houghton Mifflin. All rights reserved. Read more |
 |
| Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Latent heat". Read more |
Related answers
- What is latent heat?
- Difference between latent heat and specific latent heat?
- What is the latent heat of vaporisation?
ADVERTISEMENT
Answer these
- What is latent of heat?
- What is the importance of Latent heat in hurricanes?
- Latent heat values of water?
- Meaning of latent heat?
Mentioned in
- evaporation (physics)
- Black, Joseph (British chemist)
- decalescence (metallurgy)
- phase-change material (engineering)
- recalescence (metallurgy)
- condensation
- specific
- Bowen ratio
- hot towers
- Berthelot method (thermodynamics)
- evaporative cooling (engineering)
- heat of sublimation (thermodynamics)
- surface condenser (mechanical engineering)
- compression refrigeration (mechanical engineering)
