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

Explanation

Average bond enthalpy is the bond sissociatio enthalpy of the bonds of the same type ina molecule present in the gaseous state of a substamce. In ethanol molecule, bond enthalpy of O-H bond is not average bond enthalpy because O atom is surrounded by H and C atoms on either sides. However, it is average bond enthalpy in `H_(2)O` molecule since the two O-H bonds are similar.
`" "H-overset(H)overset(|)underset(H)underset(|)C-underset(H)underset(|)overset(H)overset(|)C-O-H" "H-O-H`