Diagrams That Provide Useful Oxidation-Reduction Information

Latimer Diagrams

Latimer or reduction potential diagrams show the standard reduction potentials connecting various oxidation states of an element. The Latimer diagram for a series of manganese species in acidic solution is shown below.
The standard reduction potential for the reduction half-reaction involving the two species joined by the arrow is shown above the arrow. Latimer diagrams show the redox information about a series of species in a very condensed form. From these diagrams you can predict the redox behavior of a given species. The more positive the standard reduction potential, the more readily the species on the left is reduced to the species on the right side of the arrow. Thus, highly positive standard reduction potentials indicate that the species at the left is a good oxidizing agent. Negative standard reduction potentials indicate that the species to the right behaves as a reducing agent. Half -reactions can be written from these diagrams.

Frost Diagrams

Frost or oxidation state diagrams plot the relative free energy of a species versus oxidation state. These diagrams visually show quite a bit about the properties of the different oxidation states of a species. Frost diagrams can be constructed from Latimer diagrams. The values to be plotted on the y-axis are obtained by multiplying the number of electrons transferred during an oxidation state change by the standard reduction potential for that change.
       The Frost Diagram for Manganese

What You Can and Cannot Learn From a Frost Diagram:

Pourbaix Diagrams

Pourbaix or eh-pH diagrams depict the thermodynamically form of an element as a function of potential and pH. The Pourbaix diagram is a type of predominance diagram -- it shows the predominate form in an element will exist under a given set of environmental conditions. These diagrams give a visual representation of the oxidizing and reducing abilities of the major stable compounds of an element and are used frequently in geochemical, environmental and corrosion applications. Like Frost diagrams, Pourbaix diagrams display thermodynamically preferred species. Kinetics is not incorporated.

How to Read a Pourbaix Diagram
   Pourbaix Diagram for Manganese

What You Can Learn From a Pourbaix Diagram


  1. Rayner-Canham, G. Descriptive Inorganic Chemistry; Freeman:New York,1996; Chapter 9.
  2. Douglas, B;McDaniel, D.; Alexander, J. Concepts and Models of Inorganic Chemistry, 3rd ed.; Wiley & Sons:New York, 1994; Chapter 8.