Inorganic and Applied Chemistry

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Inorganic and Applied Chemistry

Figure 6- 4: The galvanic iron/silver cell

Schematic setup of the Ag+/Ag and Fe2+/Fe3+ cell.

6.4 Concentration dependency of cell potentials

So far we have only looked at galvanic cells under standard conditions. Nevertheless cell potentials depend

on the concentration of the ions that are in the half cells. E.g. the following overall cell reaction:

Cu(s) + 2 Ce4+(aq)  Cu2+(aq) + 2 Ce3+(aq)

has a cell potential of 1.36 at 298 K where all ions are in 1 M concentration. Are the conditions not the

standard ones (concentration = 1.0 M, temperature = 298 K) the potential of the cell may be different. Is the

concentration of Ce4+ e.g. larger than 1 M the reaction, according to the principles of Le Charteliers, will

increase to the right and thereby increase the driving force of the cell. The cell potential will thereby increase.

The dependence of concentration for the cell potential at 298 K is given by the Nernst equation (named after

the German chemist Hermann Nernst) given as:

Y

z

celle celle log

0. 0592

+ +^0 (Standardconditions) (6- 3)

where Y is the reaction fraction found from the overall reaction equation and z is the number of transferred

electrons in the overall reaction equation. We will look further into the application of the Nernst equation in

the following example.

Electrochemistry