Thermochemistry is the study of the relationship between Chemical energy and 

Specific heat at a constant pressure (C_p) is defined by

According of first law of thermodynamics the change in internal energy. (ΔE) accompanying a process, performing a work (W) and involving absorption of heat (Q) on the surroundings is given by the relation

The internal energy of a system depends upon

In a closed system, there is 

Enthalpy H is defined as