## Application of the Nernst Equation

The following equations show the application of the Nernst equation with a simple reaction system, such as the conversion of ferrous to ferric ions by the addition of a solution containing ceric ions:

Fe2+ ® Fe3+ + e Ce4+ + e ® Ce3+ Fe2+ + Ce4+ ® Fe3+ + Ce3+

Equations 7.41(5) and (6) are half-cell reactions. Equation 7.41(5) is written in the oxidized form, i.e., the charge(s) appear to the right of the arrow, and Equation 7.41(6) is written in the reduced form, i.e., the charge(s) appear to the left of the arrow. Each half-cell reaction has a standard or half-cell electrode potential.

The terms standard electrode potential and half-cell potential are closely related; the major distinction between them is conventional. If the half-cell reaction is written in the reduced form, as in Equation 7.41(6), the standard electrode potential and the half-cell potential are the same. If the reaction is written in the oxidized form (Equation 7.41[5]), the sign of the reported potential must be changed for the half-cell potential. Butler provides more information on the sign convention of OR reactions. Table 7.41.1 gives the standard electrode potentials for Equations 7.41(5) and (6).

The Nernst equation for the two reactions is as follows:

[Fe2

[Ce3

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