3h2 (g) + o3 (g) 3h20 (g)

arrow after the o3 (g)

whats the overall enthalpy?

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