How does bond dissociation energy relate to bond strength?

1 Answer
Mar 15, 2016

Answer:

Bond strength, or bond energy, is almost but not quite the same as the bond dissociation energy we measure by experiment. There is a slight difference because breaking one bond will affect the remaining bonds.

Explanation:

Wikipedia (https://en.m.wikipedia.org/wiki/Bond-dissociation_energy) gives examples involving water and methane, let us look at the case for water. It takes 917.8 kJ/mol to break both O-H bonds, so the bond energy for each one must be half that or 458.9 kJ/mol.

But if we measure the dissociation energy for just one of the O-H bonds we get 493.4 kJ/mol, leaving just 424.4 kJ/mol for the second O-H bond. Breaking the first O-H bond had a slight impact on the remaining bond, making it weaker. So the measured (first) bond dissociation energy is the sum of the true bond energy plus the pact on the second bond.