Talk:Absolute electrode potential

This  level-5 vital article is rated Start-class on Wikipedia's content assessment scale. It is of interest to the following WikiProjects:

Chemistry Low‑importance This article is within the scope of WikiProject Chemistry, a collaborative effort to improve the coverage of chemistry on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.ChemistryWikipedia:WikiProject ChemistryTemplate:WikiProject ChemistryChemistry articles Low This article has been rated as Low-importance on the project's importance scale.

I undid an edit (and then accidentally undid the undo, and then undid that), where the definition of the absolute potential was given as -E_abs = E_relative + 4.44. However, the article says that the absolute potential of the SHE is 4.44 eV, meaning this definition becomes

E_absSHE + E_absM = -E_relative.

This definition cannot be correct, because rather than canceling the arbitrary constant in the indefinite integral that gives you an electric potential, the left hand side contains a sum of the two constants. Even if E_abs is defined as the potential relative to the potential at infinity, E_relative needs to be defined as the difference between two absolute potentials, not the sum, so something like

E_absM - E_absSHE = E_relative

Which is equivalent to the equation as it is currently defined after undoing the revision. Since I'm not extremely knowledgable about electrochemistry, I'll leave it to someone else to make sure that the article is correct stating that 4.44 is the absolute potential of the SHE and not minus the absolute potential of the SHE. Also, for all I know, there may be a silly minus sign somewhere in the definition, but that still wouldn't reduce to the first equation I wrote, because the two values on the left hand side must have opposite sign. Mpalenik (talk) 22:07, 19 July 2016 (UTC)[reply]

Note that the topic isn't about absolute and relative potentials in the physics sense. Electrochemistry uses the term "absolute" very differently than does physics. (In my experience, this is a constant source of confusion! Use care, avoid spreading more confusion.) Instead the topic is about two separate potential-differences: the potential-difference between the electrolyte and a "standard electrode," relative to the potential-difference between any other electrolyte/electrode pair. Refer to "Galvani potential" and "Volta potential," both of which are potential-differences, yet a chemist would name them "absolute potentials," because they were not measured using an SHE electrode. In other words, what electrochemists call "absolute potentials," physicsts call "potential-differences." And where chemists name the SHE as a "single electrode," physicists would stay that the electrolyte is one electrode, the metal is the other ...i.e. all half-cells have two electrodes, an electrochemical cell has four, but only two are made of metal. Confused yet? 75.172.137.74 (talk) 22:40, 5 May 2020 (UTC)[reply]

Perhaps improve the description, since we're not discussing work-function (not the potential-diff from inside the metal to outside in vacuum.) Instead, this is the potential-diff from inside the metal, and through a water layer, then out through the water/vacuum interface. This cancels the expected water/vacuum potential-diff located at all water surfaces, only leaving the potential-diff created at the layer where the SHE surface is contacting the water surface. (Because otherwise, the "absolute" potential-diff would include an unwanted potential contributed by the polarized water molecules at the liquid surface. These perhaps give constant volts, due to an electret-like effect? And so cannot contribute to Galvani potentials? Need more research! 97.113.212.162 (talk) 00:19, 7 August 2023 (UTC)[reply]