what is meant by the term average bond enthalpy? Why is there difference in bond enthalpy of O-H bond in ethanol `(C_(2)H_(5)OH)` and water?

Explanation

All the similar bonds in a molecule do not have the same bond enthaipies ,e.g., in `CH_(4) (H-underset(H)underset(|)overset(H)overset(|)C-H)`, the
four C-H bonds do not have the same bond enthapies because after breaking of the bonds one by one, the
electronic environment around carbon changes . Hence, the actual bond enthalpy of C-H bond is taken as
the averae value.
O-H bond in ethanol and that in water do not have similar electronic
enviroment around oxygen atom. Hence, their O-H bond enthalpies are different