In chemistry, the enthalpy of atomization (also atomisation in British English) is the enthalpy change that accompanies the total separation of all atoms in a chemical substance either an element or a compound. This is often represented by the symbol ⁠ Δ Δ a t H ⁠ or ⁠ Δ Δ H a t . ⁠ 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, Δ at H /(kJ mol), at 298.15 K (or 25 degrees Celsius) and 100 kPa.