Bond dissociation energy - Definition and Overview

In chemistry, bond dissociation is a process in which a specific bond is cleaved to give two new species. If a neutral molecule causes bond dissociation, it gives two free radicals. That is, two electrons that are involved in the bond are distributed one by one to the two species. This cleavage of a bond is called homolysis.

Bond dissociation is an endothermic process, and energy that is necessary to the process is called bond dissociation energy.

Strictly, the bond dissociation energy is defined as the standard reaction enthalpy of a bond fission process at 0 K (absolute zero). This standard reaction enthalpy is also called the bond dissociation enthalpy (or bond enthalpy).

The bond dissociation energy is usually different from the bond energy, which is calculated from the sum of the bond dissociation energies of all bonds in a molecule.

For example, an O-H bond of a water molecule (H-O-H) has 493.4 kJ mol^-1 of bond dissociation energy, and 424.4 kJ mol^-1 is needed to cleave the remaining O-H bond. The bond energy of the O-H bonds in water is 458.9 kJ mol^-1, which is the average of the values.

See also

• chemical bond
• binding energy