Enthalpy of atomization

The enthalpy of atomization (also standard enthalpy of atomisation - UK spelling) is the enthalpy change that accompanies the total separation of all atoms in a chemical substance (either a chemical element or a chemical compound). This is often represented by the symbol ΔHatO. The associated standard enthalpy is known as the Standard enthalpy of atomization, ΔHatO/(kJ·mol-1), at 298 K and 1 atmosphere of pressure, or 100 kPa (kilopascals.)

The enthalpy of atomization of gaseous H2O is, for example, the sum of the HO&mdash;H and H&mdash;O bond dissociation enthalpies. The enthalpy of atomization of an elemental solid is exactly the same as the enthalpy of sublimation for any elemental solid that becomes a monatomic gas upon evaporation.

There is a difference between a solid converting to a gas, and a diatomic gaseous element converting to gaseous atoms. The standard enthalpy is purely based on the production of one mole of gaseous atoms.