Electron affinity and electron gain enthalpy

Zatman

Hello,

I was wondering if someone might be able to explain these terms. Specifically, the difference between them. From what I have read they seem to describe the same thing, i.e. the enthalpy change involved in:

X(g) + e^- → X^-(g)

I am sure there is a difference that I am just not understanding. Any help would be appreciated.

DrDu

I have never run before into the term electron gain enthalpy, but electron affinity refers really to the energy (not enthalpy) difference between an atom and an ion (+electron) in vacuum.

Zatman

Hmm. Well I've read the following which confused me:

"The tendency for atoms of neutral elements to gain electrons is measured by the electron affinity. This is numerically equal to the negative of the electron gain enthalpy, which is the enthalpy change when a gas-phase atom gains an electron."

[Foundations of Inorganic Chemistry, MJ Winter and JE Andrew, p8]

Einstein Mcfly

So....what's the mystery? It's something that these guys are defining as the negative of the EA.

DrDu

lElectron affinities are most definitively energy differences and not enthalpy differences, see
http://203.158.253.140/media/e-Book/...0/10_03_87.pdf
, though the numerical difference between electron affinity and the corresponding enthalpy is small (about RT=8.3*297 J ).

Zatman

Right, confusion gone. Thanks guys!