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Encyclopedia > 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 (i.e. solid, liquid, or gas), - also called a phase transition.[1][2] The world’s first ice-calorimeter, used in the winter of 1782-83, by Antoine Lavoisier and Pierre-Simon Laplace, to determine the heat evolved in various chemical changes; calculations which were based on Joseph Black’s prior discovery of latent heat. ... For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another due to a difference in temperature. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ...


The term was introduced around 1750 by Joseph Black as derived from the Latin latere, to lie hidden. The term is now obsolete, replaced by "enthalpy of transformation". Events March 2 - Small earthquake in London, England April 4 - Small earthquake in Warrington, England August 23 - Small earthquake in Spalding, England September 30 - Small earthquake in Northampton, England November 16 – Westminster Bridge officially opened Jonas Hanway is the first Englishman to use an umbrella James Gray reveals her sex... Joseph Black Joseph Black (April 16, 1728 - December 6, 1799) was a Scottish physicist and chemist. ... t In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H or ΔH, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the useful work obtainable from a closed thermodynamic system under constant pressure. ...


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. Heat of fusion is the amount of heat energy which must be absorbed or lost for 1 gram of a substance to change states from a solid to a liquid or vice versa. ... In physics, melting is the process of heating a solid substance to a point (called the melting point) where it turns into a liquid. ... The heat of vaporization is a physical property of substances. ... Boiling, a type of phase transition, is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmospheric pressure. ...


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. In thermodynamics, the word endothermic describes a process or reaction that absorbs energy in the form of heat. ... In thermodynamics, the word exothermic describes a process or reaction that releases energy in the form of heat. ... Air redirects here. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... An air parcel is an imaginary chunk of air in the atmosphere. ... Water vapor or water vapour (see spelling differences), also aqueous vapor, is the gas phase of water. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... Sensible heat is heat energy that is transported by a body that has a temperature higher than its surroundings via conduction, convection, or both. ...

Contents

Latent Heat Equation

The equation for latent heat is:


Q = mL where:


Q is the amount of energy required to change the phase of the substance (in Joules),
m is the mass of the substance,
L is the specific latent heat for a particular substance.


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


Table of latent heats

Latent heats and change of phase temps of common fluids and gases
Substance Latent Heat
Fusion
J/g
Melting
Temp
°C
Latent Heat
Vaporization
J/g
Boiling
Temp
°C
Alcohol, Ethyl 108 -114 855 78.3
Ammonia 339 -75 1369 -33.34
Carbon Dioxide 184 -57 574 -78
Helium 21 -268.93
Hydrogen 58 -259 455 -253
Nitrogen 25.7 -210 200 -196
Oxygen 13.9 -219 213 -183
Toluene -93 351 110.6
Turpentine 293
Water 334 0 2272 100

Ethyl alcohol, also known as ethanol or grain alcohol, is a flammable, colorless chemical compound, one of the alcohols that is most often found in alcoholic beverages. ... For other uses, see Ammonia (disambiguation). ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... For other uses, see Helium (disambiguation). ... This article is about the chemistry of hydrogen. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Toluene, also known as methylbenzene or phenylmethane is a clear, water-insoluble liquid with the typical smell of paint thinners, redolent of the sweet smell of the related compound benzene. ... For the band, see Turpentine (band). ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ...

References

  1. ^ Perrot, Pierre (1998). A to Z of Thermodynamics. Oxford University Press. ISBN 0-19-856552-6. 
  2. ^ Clark, John, O.E. (2004). The Essential Dictionary of Science. Barnes & Noble Books. ISBN 0-7607-4616-8. 

See also


  Results from FactBites:
 
Heat - Wikipedia, the free encyclopedia (1619 words)
Heat flows between regions that are not in thermal equilibrium; in particular, it flows from areas of high temperature to areas of low temperature.
Latent heat is heat per unit mass necessary to change the state of a given substance.
Heat pipe: Using latent heat and capilliary action to move heat, it can carry many times as much heat as a similar sized copper rod and is starting to have applications in laptop personal computers.
  More results at FactBites »

 
 

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