THERMOCHEMISTRY, a branch of Energetics, treating of the thermal phenomena which are associated with chemical change.
The beginnings of modern thermochemistry, though made independently of the doctrine of the conservation of energy, are practically contemporaneous with the recognition of that law, and without it the science could scarcely have reached the degree of development which it rapidly attained.
When the first system then is transformed into the second, the excess of energy which the former possesses must appear in the shape of heat, light, electrical energy, mechanical energy, &c. It is for the most part a simple matter to obtain the excess of energy entirely in the form of heat, the amount of which is easily susceptible of measurement, and thus the existence of thermochemistry as a practical science is rendered possible.
The heat-units employed in thermochemistry have varied from time to time.
- What is commonly understood by thermochemistry is based entirely on the first law of thermodynamics, but of recent years great progress has been made in the study of chemical equilibrium by the application of the second law.
Reference should be made to the articles Chemical Action, Thermochemistry and Solutions, for the theory of the strength or avidity of acids.
A, 1901, " On The Variation Of The Specific Heat Of Water"; For Combustion Methods, See Article Thermochemistry, And Treatises By Thomsen, Pattison Muir And Berthelot; See Also Articles Thermodynamics And Vaporization.