I was looking at the Frost diagram of Manganese, and on the UC Davis ChemWiki, I see this one:

Frost Diagram (UC Davis)

However, the one straight from my textbook, "Descriptive Inorganic Chemistry" (Overton), looks like this:

Frost Diagram (Overton)

In the first image, the y-axis is $\mathbf{nE^o}$ and the x-axis goes from 0 to +7 from left to right, but in the second image, the y-axis is $\mathbf{-nE^o}$ and the x-axis goes from +7 to 0 from left to right.

I'm wondering if reversing the oxidation state ordering changes the y-axis definition between $nE^o$ and $-nE^o$.

It seems like a silly question to me, but I still want to be sure.

  • $\begingroup$ yep ! Write out pairs of coordinates! $\endgroup$ – porphyrin Jul 6 '16 at 7:24
  • 1
    $\begingroup$ I can't see any reason why reversing the x-axis direction should affect the y-axis in any way. I'd say one of your diagrams has it wrong. $\endgroup$ – Philipp Jul 6 '16 at 12:10

The UC Davis version is incorrect. The free energy of the system ($\Delta G$) is equal to -nFE, so y-axis is reported as $\Delta G / F$ or -nE, according to the original report by Arthur Frost (J. Am. Chem. Soc., 1951, 73 (6), 2680-2682).

Note: In the original report free energy was denoted by $\Delta F$, rather than $\Delta G$. The x-axis designation is insignificant.


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