What is "thermochemistry"

Thermochemistry \Ther`mo*chem"is*try\, n. [Thermo- + chemistry.] That branch of chemical science which includes the investigation of the various relations existing between chemical action and that manifestation of force termed heat, or the determination of the heat evolved by, or employed in, chemical actions.

also thermo-chemistry, 1840, from thermo- + chemistry.

n. (context chemistry physics English) The study of the thermodynamics of chemical reactions.

Thermochemistry is the study of the energy and heat associated with chemical reactions and/or physical transformations. A reaction may release or absorb energy, and a phase change may do the same, such as in melting and boiling. Thermochemistry focuses on these energy changes, particularly on the system's energy exchange with its surroundings. Thermochemistry is useful in predicting reactant and product quantities throughout the course of a given reaction. In combination with entropy determinations, it is also used to predict whether a reaction is spontaneous or non-spontaneous, favorable or unfavorable.

Endothermic reactions absorb heat, while exothermic reactions release heat. Thermochemistry coalesces the concepts of thermodynamics with the concept of energy in the form of chemical bonds. The subject commonly includes calculations of such quantities as heat capacity, heat of combustion, heat of formation, enthalpy, entropy, free energy, and calories.