Thermochemistry

From Wikipedia, the free encyclopedia

The world’s first ice-calorimeter, used in the winter of 1782-83, by Antoine Lavoisier and Pierre-Simon Laplace, to determine the heat evolved in various chemical changes; calculations which were based on Joseph Black’s prior discovery of latent heat. These experiments mark the foundation of thermochemistry.

In thermodynamics and physical chemistry, thermochemistry is the study of the energy evolved or absorbed in chemical reactions and any physical transformations, such as melting and boiling. Thermochemistry, generally, is concerned with the energy exchange accompanying transformations, such as mixing, phase transitions, chemical reactions, and including calculations of such quantities as the heat capacity, heat of combustion, heat of formation, enthalpy, and free energy.

[edit] History

Thermochemistry rests on two generalizations:^[1]

1. Lavoisier and Laplace’s law (1782): the heat exchange accompanying a transformation is equal and opposite to the heat exchange accompanying the reverse transformation.
2. Hess's law (1840): the heat exchange accompanying a transformation is the same whether the process occurs in one or both steps

Both of these statements preceded the first law of thermodynamics (1850) and helped in its formulation.

Lavoisier, Laplace and Hess also investigated specific heat and latent heat, although it was Joseph Black who made the most important contributions to the development of latent energy changes.

[edit] Calorimetry

The measurement of heat changes is performed using calorimetry, usually an enclosed chamber within which the change to be examined occurs. The temperature of the chamber is monitored either using a thermometer or thermocouple, and the temperature plotted against time to give a graph from which fundamental quantities can be calculated. Modern calorimeters are frequently supplied with automatic devices to provide a quick read-out of information, one example being the DSC or differential scanning calorimeter.

[edit] See also

Science portal

• Differential scanning calorimetry
• Important publications in thermochemistry
• Isodesmic reaction
• Principle of maximum work
• Reaction Calorimeter
• Thomsen-Berthelot principle
• Julius Thomsen
• Thermodynamic databases for pure substances
• Calorimetry

[edit] References

1. ^ Perrot, Pierre (1998). A to Z of Thermodynamics. Oxford University Press. ISBN 0-19-856552-6. 

[edit] External links

• Thermochemistry - Britannica (1911)
• Thermochemistry - an overview