Enthalpy of Reaction Definition

Enthalpy of Reaction
By Urs von Stockar [CC BY-SA 2.5 (https://creativecommons.org/licenses/by-sa/2.5)], from Wikimedia Commons 

The enthalpy of reaction (ΔHRXN) is the difference between the total enthalpy of the products of a reaction and the total enthalpy of the reactants.