Electron gain enthalpy and electron affinity are essentially the same concept, but with a sign convention difference. Electron gain enthalpy is the energy change when an atom gains an electron, with negative values indicating energy release. Electron affinity is traditionally defined as the energy released when an atom gains an electron, so it has the opposite sign of electron gain enthalpy.

Electron gain enthalpy = Electron affinity – 52RT, where R is the universal gas constant and T is the temperature in kelvin.