Since most reactions do not end up with all the constituent atoms as free ions, the real question is how the sum of bond energies of the reaction product(s) compares to the sum of bond energies of the starting molecule(s).

In the case of water, 2 H20 -> 2 H2 + O2 is endothermic, but reactions do not have to be endothermic, or else chemistry would be very boring and cold.