text: Thermal expansion occurs because models for this quantity versus separation distance are asymmetric.
full_question: Thermal expansion occurs because models for this quantity versus separation distance are asymmetric. This quantity is approximately the height of the well of a Morse potential. For a binary acid, this quantity equals proton affinity plus electron affinity minus ionization energy. It is exactly equal to the heat of reaction for homolysis, forming radicals. Though not heat of formation, this quantity is quite low for peroxides, explaining their (*) explosiveness. The heat of reaction equals the sum over this quantity for each of the reactants minus the sum of it for the products. It varies inversely with length and directly with order. For 10 points, name this quantity, the amount of energy released when two molecular fragments link covalently.
first_sentence: Thermal expansion occurs because models for this quantity versus separation distance are asymmetric.
raw_answer: bond energy [or bond dissociation energy; or BDE; or bond strength; prompt on stability]