Enthalpy of atomization

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 a chemical element or a chemical compound).^[1] This is often represented by the symbol Δ_atH or ΔH_at. 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_atH^o/(kJ mol⁻¹), at 298.15 K (or 25 degrees Celsius) and 100 kPa.

Definition

Enthalpy of atomization is the amount of enthalpy change when a compound's bonds are broken and the component atoms are separated into individual atoms.

Enthalpy of atomization is denoted by the symbol Δ_atH. The enthalpy change of atomization of gaseous H₂O is, for example, the sum of the HO–H and H–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.

When a diatomic element is converted to gaseous atoms, only half a mole of molecules will be needed, as the standard enthalpy change is based purely on the production of one mole of gaseous atoms. When the atoms in the molecule are different isotopes of the same element the calculation becomes non-trivial.

Standard enthalpy of atomization is the enthalpy change when 1 mol of a substance is dissociated completely into atoms under standard conditions (298.15K, 1 bar).

See also

• Ionization energy
• Electron gain enthalpy

References