relation between enthalpy of reaction and bond enthalpy
Answers
OK, here is the difference: formation enthalpy refers to the formation of a compound from elementary compounds, while bond energy is applicable when considering the formation of a molecule from isolated atoms. The relation between the two is pretty much explained by the Hess's law: the enthalpy of a reaction does not depend on its pathway, but only on the initial and final states.
Now consider the following two pathways for your example.
Pathway 1: we burn graphite in oxygen, just like C+O2⟶CO2. There is some change of enthalpy associated with this reaction.
Pathway 2: we vaporize graphite to get atomic carbon (see how many C-C bonds are broken, take that into account), atomize O2 to get elementary oxygen (again, some bonds are broken), and finally produce CO2 (this time some bonds are formed). Now if you'll look up the energies of all bonds involved and carefully add/subtract them all together, you'll have a decent approximation of the reaction enthalpy obtained in the pathway 1.