, Volume 4, Issue 1, pp 1-9
Date: 14 Nov 2012

Do You Really Understand the Electrochemical Nernst Equation?

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Introduction

If you ask undergraduate students of Chemistry “Do you understand the electrochemical Nernst equation [1]?”, a high percentage of them will answer “Of course, we do! It is the equation that relates the activity of the species taking part in an electrochemical equilibrium to its electrode potential!” The next question: “So, would you be able to calculate how the electrode potential of the reaction1$$ \mathrm{A}+{{\mathrm{H}}^{+}}+{{\mathrm{e}}^{-}}\rightleftarrows \mathrm{D} $$changes with pH?” will also be answered by a high percentage of students with a “yes, we would.” It is given by:2$$ E={E^0}+\frac{RT }{F}\ln \frac{{{a_{\mathrm{A}}}.{a_{{{{\mathrm{H}}^{+}}}}}}}{{{a_{\mathrm{D}}}}}={E^0}+\frac{RT }{F}\ln \frac{{{a_{\mathrm{A}}}}}{{{a_{\mathrm{D}}}}}-\frac{2.3RT }{F}pH $$where Eo stands for the standard electrode potential and a for the activity of the different compounds that take part in the reaction”. But if you go deeper into the problem asking for example, “Do you t