Bond energies are determined (measured and/or calculated) for gases only. This is done to eliminate interference from other interactions of molecules or ions at close range.

Second, most bond energies are averages. For simple diatomic molecules which actually exist like HF or H₂ the bond energy can be measured very accurately. But in a molecule such as H₂O, the energy required to break the two H-O bonds is not exactly the same. So lots of data on similar molecules is used to make an average (note the different numbers of significant digits in the values).

Moral: to be able to predict the enthalpy change for a reaction, we either need to do an experiment or we need a better calculation method. Stay tuned.......