Calorimetry is the science of measuring the heat of chemical reactions or physical changes. Calorimetry involves the use of a calorimeter. The word calorimetry is derived from the Latin word calor, meaning heat.

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. Lavosier noted in 1780 that heat production can be predicted from oxygen comsumption this way, using multiple regression. The Dynamic Energy Budget theory explains why this is 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.

Temperature and Internal Energy

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If an object or system is isolated from the rest of the universe, its temperature must stay constant. If energy enters or leaves, the temperature must change. Energy moving from one place to another is called heat and calorimetry uses measurement of temperature change, along with heat capacity, to track the movement of heat.

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:

$q\; =\; C\_V\; \backslash Delta\; t\; =\; \backslash Delta\; U\; \backslash ,$

where

ΔU = change in internal energy

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:

$q\; =\; \backslash Delta\; U\; -\; w\; \backslash ,$

Since in constant-pressure calorimetry, pressure is kept constant, the heat measured represents the enthalpy change:

$q\; =\; \backslash Delta\; H\; =\; H\_\backslash mathrm\{final\}\; -\; H\_\backslash mathrm\{initial\}\; \backslash ,$

See also

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• Enthalpy
• Differential scanning calorimetry
• Isothermic titration calorimetry
• Respirometry

External links

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• Coflux - A new method of reaction calorimetry
• More Information, History - from Parr with over 100 years of Calorimetry

Thermodynamics | Heat | Kalorimetrie | Calorimetría | Calorimétrie | Калориметрия