Definitions for "Heat of reaction"
Energy that must be supplied in the form of heat to keep a system at constant temperature and pressure during a reaction.
The heat of reaction describes the 'enthalpy' which is given off or absorbed during a reaction. If the pressure of the reaction remains constant, you can think of enthalpy as simply being heat.
the heat released or absorbed during a chemical change; equivalent to the change in enthalpy, ΔH, when the change takes place in the amounts indicated by the thermochemical equation.