Why is a polar covalent bond stronger than a non-polar covalent bond?

Answer 1

Well! First some facs - H2 bond disocciation energy is 432 kJ/mol. This is greater than HCl (428 kcal/mol) so the simple statement is false.

Pauling put this idea forward, he analysed bond strengths in terms of valence bond theory and the idea of resonance between a pure covalent bond and an ionic bond. Where the energy of the pure covalent and ionic was very close together there was a considereable strengthening of the bond. In the simple case of the hydrogen halides this criterion was met most closely by HF and the bond energy of this highly polar molecule was stronger than both the pure covalent or pure ionic forms.

Pauling "invented" the concept of electrnegativity through this method of analysing bond strengths.