Ionisation enthalpy is the enthalpy change associated with the ionisation of an atom, that is, with removing an electron at constant pressure; it is usually expressed in kilojoules per mole (kJ/mol). It is closely related to the ionisation energy but is quoted as a molar, constant-pressure quantity. Like ionisation energy, it is a positive (endothermic) quantity.

电离焓是与原子电离(即在恒压下移除一个电子)相关的焓变,通常以千焦每摩尔(kJ/mol)表示。它与电离能密切相关,但以每摩尔、恒压的量给出。与电离能一样,它是正值(吸热)。