Bond Dissociation Enthalpy
The enthalpy change when one mole of a specific bond is broken homolytically in the gas phase.
Formula / equation
A–B(g) → A·(g) + B·(g)
Unit
kJ/mol
In depth
Unlike average bond energies, dissociation enthalpies are defined for one particular bond in one particular molecule, and successive values differ: removing the four hydrogens from methane requires four different energies. Bond dissociation enthalpy is always positive.
Examples in the real world
The first C–H bond in methane needs 439 kJ/mol, while the average C–H value quoted in tables is 413.