This episode explains how to calculate the enthalpy of a reaction (ΔHrxn​) using average bond enthalpies. This method is based on the principle that breaking old bonds requires energy and forming new bonds releases energy. The core formula is ΔHrxn​=Σ(bonds broken)−Σ(bonds formed), where "bonds broken" refers to the energy of the reactant bonds and "bonds formed" is the energy of the product bonds.