The proton affinity, Epa, of an anion or of a neutral atom or molecule is a measure of its gas-phase basicity. It is the energy released in the following reactions:
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- A− + H+ → HA
- B + H+ → BH+
These reactions are always exergonic in the gas phase, i.e. energy is released when the reaction advances in the direction shown. However, proton affinities are conventionally quoted with the opposite sign convention from most other thermodynamic properties, a positive Epa indicating a release of energy by the system. This is the same sign convention as is used for electron affinity.
Read more about Proton Affinity: Acid/base Chemistry, Hydration, Difference From PKa, See Also
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