Calorimetry is the science of measuring the heat of chemical reactions or physical changes. Calorimetry involves the use of a calorimeter.
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:
Since in constant-volume calorimetry 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:
Since in constant-pressure calorimetry, pressure is kept constant, the heat measured represents the enthalpy change:
See also
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