Calorimetry

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:

<math>q = C \Delta t = \Delta U \,<math>

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:

<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>

See also

• enthalpy

External links

• More Information, History – from Parr with over 100 years of Calorimetry