Bond dissociation energy

Bond dissociation energy is the energy required to break a specified chemical bond homolytically in the gas phase, producing two radicals. It depends on the molecular environment of the bond.

Homolytic bond cleavage: Bond breaking in which each bonded atom retains one electron from the shared pair. This is the specific cleavage process whose energy bond dissociation energy measures.
Bond energy–bond enthalpy relationship: The use of bond enthalpies to estimate reaction enthalpy from bonds broken and formed. Dissociation energies provide bond-specific inputs to approximate reaction energetics.
Enthalpy: A thermodynamic state function equal to internal energy plus pressure multiplied by volume. Many tabulated bond dissociation values are enthalpy changes rather than raw energy differences.
Bond-dissociation enthalpy: The enthalpy change for homolytically breaking a specified bond in the gas phase. It is often called bond dissociation energy, though enthalpy and energy are distinct quantities.
Carbon–hydrogen bond: A covalent bond between a carbon atom and a hydrogen atom. Its dissociation energy varies substantially with the structure of the carbon-centered radical formed.
Bond dissociation energy curve: A potential-energy curve describing how molecular energy changes as a bond is stretched and broken. Its dissociation limit gives the energy needed to separate the bonded fragments.
Combustion: A chemical reaction in which a fuel reacts rapidly with an oxidant, commonly releasing heat and light. Bond breaking and formation energies help account for combustion’s heat release.
Standard enthalpy of formation: The enthalpy change when one mole of a substance forms from its elements in standard states. Formation enthalpies let chemists calculate bond dissociation enthalpies with Hess’s law.
Bond dissociation free energy: The Gibbs free-energy change for homolytically breaking a specified bond under stated conditions. Entropy contributions make this free-energy measure differ from bond dissociation energy.
Oxygen–hydrogen bond: A covalent bond between an oxygen atom and a hydrogen atom. Its strength helps explain hydrogen donation by water, alcohols, and antioxidants.

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