Calorimetry is the science of measuring the heat of chemical reactions or physical changes. Calorimetry involves the use of a calorimeter.

Contents

1 Constant-volume 2 Constant-pressure 1 See also 2 External links

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 (http://www.parrinst.com?page_id=183)

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