The definition of bond enthapy is energy to break 1 mol of a bond in the gas [hase.

When the bond is breaking, the energy is added.  When the bond is forming, the energy is released.

So in general reactants --> products chemical equation,

Bond enthalpy is always positive in forward reaction, and the bond enthapy is always negative for reverse reaction.

For the forward reaction, reactants are breaking bonds and products are forming new bonds.  

Therefore, delta H = energy to break bonds + energy to forming bonds

+                               -

= + bond energy for reactants + (-) bond eneryg for products

= bond energy for reactants - bond eneryg for product