Thermal energy
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225659881
2008-07-14T19:51:38Z
Cardamon
2007187
Revert good faith edits by anon to last version by Cluebot.
In [[thermal physics]], '''thermal energy''' is the [[energy]] portion of a [[thermodynamic system|system]] that increases with its [[temperature]]. In a loose sense, "thermal energy" is a term used to describe the energy content of a system related to [[heating]] effects, e.g. temperature increase or decrease. In [[thermodynamics]], thermal energy is the [[internal energy]] present in a system in a state of [[thermodynamic equilibrium]] by virtue of its temperature.<ref>[http://www.britannica.com /eb/article-9072068/thermal-energy Thermal energy] - Britannica</ref> The term is not widely used, however, in a rigorous sense, owing to the result that the phrase "thermal ([[heat]]) energy" is counter-intuitive. That is, "thermal energy" can only be defined as any spontaneous ''flow of energy'' (energy in transit) from one object to another, caused by a difference in temperature between two objects; thus, an object cannot possess "heat".<ref name="Schroeder" >{{cite book|author= Schroeder, Daniel, R.|title=Thermal Physics|publisher=New York: Addison Wesley Longman|year=2000|id=ISBN 0201380277}}</ref> This is explained by the [[second law of thermodynamics]]. Hence, by extrapolation, it is difficult to define quantities of heat energy (thermal energy). In isolated cases, however, a few definitions do exist.
==Internal energy ==
'''[[Internal energy]]''' – the sum of all microscopic forms of energy of a system. It is related to the molecular structure and the degree of molecular activity and may be viewed as the sum of kinetic and potential energies of the molecules; it consists of the following types of energies:<ref>{{cite book | last = Cengel | first = Yungus, A. | coauthors = Boles, Michael | title = Thermodynamics - An Engineering Approach, 4th ed. | pages = 17-18 | publisher = McGraw-Hill | year = 2002 | id = ISBN 0-07-238332-1}}</ref>
<center>
{| border="1" cellpadding="2"
! Type !! Composition of '''[[Internal Energy]]''' (U)
|-
! '''[[Sensible heat|Sensible energy]]'''
|width="700pt" align="left" | the portion of the [[internal energy]] of a system associated with kinetic energies (molecular translation, rotation, and vibration; electron translation and spin; and nuclear spin) of the molecules.
|-
! '''[[Latent heat|Latent energy]]'''
|width="700pt" align="left" | the internal energy associated with the [[states of matter|phase]] (i.e. solid, liquid, or gas), of a system/material.
|-
! '''[[Chemical energy]]'''
|width="700pt" align="left" |the internal energy associated with the [[chemical bonds|atomic bond]]s in a molecule.
|-
! '''[[Nuclear energy]]'''
|width="700pt" align="left" |the tremendous amount of energy associated with the [[nuclear energy|strong bond]]s within the nucleus of the atom itself.
|-
! '''[[Fundamental interactions|Energy interaction]]s'''
|width="700pt" align="left" |those types of energies not stored in the system (e.g. [[heat transfer]], [[mass transfer]], and [[Work (thermodynamics)|work]]), but which are recognized at the [[thermodynamic system|system boundary]] as they cross it, which represent gains or losses by a system during a process.
|-
! '''[[Thermal energy]]'''
|width="700pt" align="left" |the sum of sensible and latent forms of internal energy.
|}
</center>
==Definitions==
===System of N particles===
According to the [[equipartition theorem]], it is possible to define thermal energy. In a system of ''N'' molecules, each with f degrees of freedom, and if there are no other (non-quadratic) temperature-dependent forms of energy, then the total thermal energy of the system is:<ref name="Schroeder" />
:<math>U_{thermal} = N \cdot f \cdot \frac{1}{2}kT.</math>
To note, ''U<sub>thermal</sub>'' is almost never the total energy of a system; for instance, there can be static energy that doesn't change with temperature, such as [[bond energy]] or rest energy (E=mc<sup>2</sup>).
===Other definitions===
Thermal energy per particle is also called the average translational kinetic energy possessed by free particles given by equipartition of energy.<ref>[http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/eqpar.html#c2 Thermal energy] – Hyperphysics</ref>
Thermal energy is the difference between the [[internal energy]] of an object and the amount that it would have at [[absolute zero]].{{Fact|date=July 2007}} It includes the quantity of [[kinetic energy]] due to the motion of the internal particles of an object, and is increased by [[heating]] and reduced by [[cooling]].
In a [[monatomic]] [[ideal gas]], the thermal energy is exactly given by the kinetic energy of the constituent particles.{{Fact|date=July 2007}}
==See also==
{{col-start}}
{{col-break}}
*[[Enthalpy]]
*[[Entropy]]
*[[Heat transfer]]
{{col-break}}
*[[Radiation]]
*[[Thermal efficiency]]
*[[Thermal science]]
{{col-end}}
==References==
<references/>
[[Category:Thermodynamics|Energy]]
[[Category:Heat]]
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