Combustion is a familiar example of the transformation of chemical energy into heat and light; the quantitative measures of heat evolution or absorption (heat of combustion or combination), and the deductions therefrom, are treated in the article Thermochemistry.
The alchemists used the terms fermentation, digestion and putrefaction indiscriminately; any reaction in which chemical energy was displayed in some form or other - such, for instance, as the effervescence occasioned by the addition of an acid to an alkaline solution - was described as a fermentation (Lat.
Transformations of electrical into chemical energy are witnessed in the processes of electrolysis (q.v.; see also Electrochemistry and Electrometallurgy).
Another branch, related to energetics, is concerned with the transformation of chemical energy into other forms of energy - heat, light, electricity.