Another way to determine the enthalpy of reaction is by using tabulated bond dissociation energies. You can apply this in a similar manner to how we used standard enthalpies of formation. Using bond energy to calculate the enthalpy of reaction is not particularly accurate because energies are affected by each molecule's unique surroundings, such as intermolecular forces. For this reason, energies are only an average across many different reactions.
Watch this video, which shows a worked example of this type of problem.