Chemistry Stack Exchange is a question and answer site for scientists, academics, teachers, and students in the field of chemistry. It only takes a minute to sign up.
Sign up to join this community
From Wikipedia:
What does this graph mean?
What is $\varepsilon$? It looks like $\varepsilon_0$, like the vacuum permittivity, but what does this have to do with the polymorph and/or isomers of ferrite or hematite?
And what is the V or 'five' in square brackets after the $\varepsilon_0$?
This diagram, called E-pH diagram or Pourbaix diagram, makes it possible to know the domains of existence or of predominance of redox species as a function of pH.
The abscissa is the pH, the ordinate the reduction potential (with respect to the standard hydrogen electrode): thus, it is not a question of the size epsilon but of the potential $E$ which has been a little "stylized" as $\mathcal{E}$, which is expressed in volts (hence the symbol V).
This is a Pourbaix Diagram (I assume this is where you got this figure). While it's not a common notation as far as I'm aware, $\epsilon_0$ is being used to represent the reduction potential in volts (V). As mentioned at the top of the Wikipedia page, this is basically a phase diagram, that tells you the ranges of voltage/pH for which a particular species of (in this case) iron is most thermodynamically favorable. The dividing lines coincide with an even mixture of the surrounding species.
$\mathcal{E}_0$, as in electromotive force.
$\endgroup$
– orthocresol♦
Feb 13 at 2:14
