Everything about Calorimetry totally explained
Calorimetry is the
science of counting 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. 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.
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):
»
where
» ΔU is change in
internal energy,
ΔT is change in
temperature and
» CV is the
heat capacity at constant volume.
Since in
constant-volume calorimetry the
pressure isn't kept constant, the heat measured doesn't 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:
»
Since in
constant-pressure calorimetry,
pressure is kept constant, the heat measured represents the
enthalpy change:
»
This formula is a simplified representative of
Hess's Law.
Further Information
Get more info on 'Calorimetry'.
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