Calorimetry
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2008-06-17T11:39:31Z
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[[Image:Ice-calorimeter.jpg|250px|right|thumb|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 change]]s; calculations which were based on [[Joseph Black]]’s prior discovery of [[latent heat]]. These experiments mark the foundation of [[thermochemistry]].]]
'''Calorimetry''' is the [[science]] of measuring the [[heat]] of [[chemical reaction]]s or [[physical change]]s. Calorimetry involves the use of a [[calorimeter]]. The word calorimetry is derived from the Latin word ''calor'', meaning heat. Scottish physician and scientist [[Joseph Black]], who was the first to recognize the distinction between [[heat]] and [[temperature]], is said to be the founder of calorimetry.<ref name="Laider" >{{cite book|author= Laider, Keith, J.|title=The World of Physical Chemistry|publisher=Oxford University Press|year=1993|id=ISBN 0-19-855919-4}}</ref>
'''Indirect calorimetry''' calculates [[heat]] that living organisms produce from their production of [[carbon dioxide]] and nitrogen waste (frequently [[ammonia]] in aquatic organisms, or [[urea]] in terrestrial ones), OR from their consumption of [[oxygen]].
Lavoisier noted in 1780 that heat production can be predicted from oxygen consumption this way, using [[multiple regression]]. The [[Dynamic Energy Budget]] theory explains why this procedure is correct. Of course, heat generated by living organisms may also be measured by '''direct calorimetry''', in which the entire organism is placed inside the calorimeter for the measurement.
==Types==
Calorimetry is performed using one of two methods: constant volume or constant pressure.
===Constant-volume===
''Constant-volume calorimetry'' is calorimetry performed at a constant [[volume]]. This involves the use of a [[constant-volume calorimeter]].
No work is performed in constant-volume calorimetry, so the heat measured equals the change in internal energy of the system. The equation for constant-volume calorimetry is (the heat capacity at constant volume is assumed to be constant):
:<math>q = C_V \Delta T = \Delta U \,</math>
where
:''ΔU'' is change in [[internal energy]],
:''ΔT'' is change in [[temperature]] and
:''C<sub>V</sub>'' is the [[heat capacity]] at constant volume.
Since in ''constant-volume calorimetry'' the [[pressure]] is not kept constant, the heat measured does not represent the ''[[enthalpy]] change.
===Constant-pressure===
''Constant-pressure calorimetry'' is calorimetry performed at a constant [[pressure]]. This involves the use of a [[constant-pressure calorimeter]].
The heat measured equals the change in internal energy of the system minus the work performed:
: <math> q = \Delta U - w \,</math>
Since in ''constant-pressure calorimetry'', [[pressure]] is kept constant, the heat measured represents the ''[[enthalpy]] change'':
: <math>q = \Delta H = H_\mathrm{final} - H_\mathrm{initial} \,</math>
This formula is a simplified representative of [[Hess's Law]].
==See also==
* [[Accelerating rate calorimetry]]
* [[Differential scanning calorimetry]]
* [[Isothermal titration calorimetry]]
* [[Respirometry]]
* [[Thermodynamic databases for pure substances]]
* [[Thermochemistry]]
==References==
{{Reflist}}
[[Category:Heat]]
[[Category:Thermodynamics]]
[[Category:Calorimetry]]
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{{Analytical chemistry}}
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