Frost diagram
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2008-05-30T20:53:08Z
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A '''Frost diagram''' is an Oxidation State Free Energy Diagram (O.S.F.E), also known as an Eh-pH diagram, due to its axial labellings, and is used in [[electrochemistry]] to illustrate the relative stability of a number of different [[oxidation state]]s of a particular substance. Frost diagrams will be different at different [[pH]]s so the pH must be specified.
The [[pH]] dependence is given by the factor -0.059m/n per pH unit, where m relates to the number of [[protons]] in the equation, and n the number of [[electrons]] exchanged. [[Electrons]] are always exchanged in [[electrochemistry]], but not necessarily [[protons]]. If there is no [[proton]] exchange in the reaction equilibrium, the reaction is said to be ''pH independent''. This means that the values for the electrochemical potential rendered in a [[redox]] [[half-reaction]] whereby the [[element]]/s in question change/s [[oxidation state]] are the same whatever the pH conditions under which the procedure is carried out.
On a Frost diagram the [[element]] is generally set as the reference point at 0 Volts.
The lower a point is on the Frost Diagram, the more stable it is. This indicates the most stable oxidation state for that element.
Points found high in the upper left indicate an element that will act as a strong oxidizing agent at that oxidation state [http://www.wou.edu/las/physci/ch462/redox.htm].
The gradient of the line between any two points on a Frost Diagram give the potential for the reaction. A species which lies in a peak, above the gradient of the two points on either side, denotes a species unstable with respect to [[disproportionation]], and a point which falls below the gradient of the line joining its two adjacent points lies in a [[thermodynamic]] sink, and is ''intrinsically stable''.
The axes of the Frost diagram show (horizontally) the oxidation state of the species in question and (vertically) the electron exchange number multiplied by the voltage (nE) OR the [[Gibbs free energy]] per unit of the [[Faraday constant]], ΔG/F.
An example of a Frost diagram: [http://facstaff.unca.edu/gheard/chem328/notes/V_frost.gif]
[[Category:Electrochemistry]]
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