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. 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 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.
Energy expenditure and psychological stateEdit
Temperature and Internal Energy Edit
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.
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:
- ΔU = change in internal energy
The heat measured equals the change in internal energy of the system minus the work performed:
Since in constant-pressure calorimetry, pressure is kept constant, the heat measured represents the enthalpy change:
See also Edit
- Differential scanning calorimetry
- Isothermal titration calorimetry
- Accelerating rate calorimetry
- Thermodynamic databases for pure substances
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