Bond dissociation energies describe the strength of chemical bonds. They can be determined experimentally. We’ll need some basic math for this section. 

Enthalpy (ΔH°) is the sum of bond dissociation energies for the reaction.

  • Negative values (-) indicate the making of new bonds = Exothermic
  • Positive values (+) indicate the breaking of new bonds = Endothermic

Problem: Predict the sign and magnitude of ∆Ho in kj/mol for the following reaction. Identify the reaction as either exothermic or endothermic.