Question

what is difference between electron affinity and electron gain enthalpy

Answer 1

Electron Gain Enthalpy is the energy released when one mole of electron are added to gaseous atoms of an element. Electron Affinity is the same as Electron Gain Enthalpy but viewed as the energy supplied to the surroundings rather than that released by the atoms. Hence its sign is opposite from the latter.

Answer 2

Answer:

definition of electron gain enthalpy (ΔegH) is : the heat or enthalpy change (kJ/mol) associated with an isolated neutral gaseous atom when it gains an electron.

The definition of electron affinity is : the change in energy of a neutral isolated gaseous atom when an electron is added to the atom to form a negative ion.

So, both the terms are basically the same I believe. The difference is that Electron affinity is the negative of electron gain enthalpy. Well it does make sense if you look at the meaning of the word “electron affinity“... not the textbook definition, but the direct meaning of the words electron & affinity. It has something to do with the attraction or love towards electrons.

Let‘s take the case of a non metal X with 6 valence electrons. When they gain an electron some amount of energy is released. This is electron gain enthalpy. This energy is negative according to thermodynamics. and since it is a non metal, it has a tendency to gain electron. So, the electron affinity would be positive.

but in the case metals, they tend to lose electrons. so, the electron affinity would be negative.

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Another difference between these two terms is that electron affinity is defined only at absolute zero. So at an other temperature we need to have another heat capacity quantity which is electron gain enthalpy. Therefore at regular temperature we use electron gain enthalpy.