The overall enthalpy of reaction will be calculated from enthalpy of formation of products and reactants.
DeltaHrxn = [Sum of enthalpy of formation of products] - [sum of enthalpy of formation of reactants]
DeltaHrxn = 3 X deltaHf (H2O) - [ 3 X DeltaH (H2) + DeltaH (O3)]
DeltaHrxn = 3 X (--242) - [ 0 + 143] = -869 kJ / mole
We can also calculate the enthalpy of reaction from bond energies
