thermochemistry n 1: the branch of chemistry that studies the relation between chemical action and the amount of heat absorbed or generated
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. [1913 Webster]