What is enthalpy of atomisation?

The enthalpy of atomization is the enthalpy change that accompanies the total separation of all atoms in a chemical substance. This is often represented by the symbol ΔₐₜH or ΔHₐₜ. All bonds in the compound are broken in atomization and none are formed, so enthalpies of atomization are always positive.
Enthalpy of atomization, ΔaH0, is the change in enthalpy when one mole of bonds is completely broken to obtain atoms in the gas phase. For example: atomization of methane molecule.CH4\xa0(g) →\xa0C (g) + 4H (g) ΔaH0= 1665.0 kJ mol-1For\xa0diatomic molecules, enthalpy of atomization is equal to the enthalpy of bond dissociation. For example: atomization of dihydrogen molecule.H2\xa0(g) → 2H (g); ΔaH0= 435.0 kJ mol-1