Chemistry is a branch of science. However, because the subject itself is so vast it is divided into many sub types in order to make it easier to navigate. Thermos chemistry is the study of heat energy. The energy that is given out during chemical reactions or taken in during chemical reactions. The enthalpy changes, whether a reaction will take place or not.
All of these different aspects are covered in thermochemistry. Basically, to sum it all up, thermochemistry determines the likelihood of a reaction occurring for real. It also corresponds to the heat energy that is associated with physical transformations.
