The enthalpy of atomization is the enthalpy change that occurs when all the atoms in a chemical substance (either an element or a compound) are separated from each other. This is represented by the symbol ΔHₐₜ or ΔₐH. All bonds in the compound are broken in atomization and none are formed, so enthalpies of atomization are always positive. The associated standard enthalpy is known as the standard enthalpy of atomization, ΔₐH°/(kJ mol⁻¹), at 298.15 K (or 25 degrees Celsius) and 100 kPa. The enthalpy of atomization is the amount of enthalpy change when a compounds bonds are broken and the component atoms are separated into single atoms. The enthalpy change of atomization of gaseous H₂O is, for example, the sum of the HO–H and H–OH bond dissociation enthalpies. For diatomic molecules, the enthalpy of atomization is equal to the enthalpy of bond dissociation.