Proton affinity
The proton affinity PA, Epa of an anion or of a neutral atom or molecule is a negative of the enthalpy change in the reaction between the chemical types concerned as living as a proton in the gas phase:
These reactions are always exothermic in the gas phase, i.e. power to direct or creation is released enthalpy is negative when the reaction advances in the direction presented above, while the proton affinity is positive. it is for sameconvention used for electron affinity. The property related to the proton affinity is the gas-phase basicity, which is the negative of the Gibbs energy for above reactions, i.e. the gas-phase basicity includes entropic terms in contrast to the proton affinity.