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A new 3-D graphical representation of oxidation–reduction (redox) processes in aqueous solutions has been developed utilizing a composition grid for which the x-axis carries the activity of the reduced form of the redox couple and the y-axis carries the activity of the oxidized form. The Nernst equation potential corresponding to the redox couple’s activities at each grid point is plotted above it as a z-coordinate. This creates a 3-D trend surface (a topo) over the grid. The topos typically have a steep left-hand bluff and a precipitous front cliff that are encountered when one or the other of the redox couple species is near depletion. In between these two features, much of the topo is a broad plateau with an elevation near the E0 for the half-reaction. Discharge paths during the operation of a galvanic cell appear as oppositely-trending, angled paths across a pair of vertically-separated surfaces. The cell dies when the two reaction paths achieve the same potential, i.e., identical z-coordinates. Redox TOPOS, a free downloadable Microsoft Excel workbook, generates 1681-point (41 x 41) 3-D topos once a redox couple has been identified and all Nernst equation parameters have been entered. Also included are a set of PowerPoint lecture slides and a document “Teaching with Redox TOPOS” containing sections for use in lecture and exercises for homework or discussion for introductory college courses and upper division or graduate physical chemistry, analytical chemistry, biochemistry, and geochemistry courses.
© 2021 Garon C. Smith and Md Mainul Hossain
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Smith, Garon C. and Hossain, Md Mainul, "Chapter 3.1: Visualization of the Nernst Equation Via 3-D Topo Surfaces: E⁰ Plateaus, Left-Hand Bluffs, Front Cliffs and Reaction Paths" (2021). Water Topos: A 3-D Trend Surface Approach to Viewing and Teaching Aqueous Equilibrium Chemistry. 8.