Cell Potential

What is cell potential?

Cell potential is the ability to produce an electric current. You cannot have a potential for a half-cell. You need two connected half-cells.

Cell potential results from the competition for electrons between half-cells.

You can find the cell potential by using the below equation:

Ecell = Ered — Eoxid

You can find the half-cell's potential by looking it up on a table of standard cell potentials.

Standard cell is the measured cell potential with the half cells at 1M, standard pressure (101kPa) and 25 °C. Standard cell potentials are all relative, so hydrogen is used as the basis for comparison.

Calculating Cell Potential

For example, if you have a cell made with zinc and silver.

Identify which metal will be reduced and which will be oxidized.

Silver (Ag) is higher than zinc (Zn) on the table, so silver will be reduced and zinc will be oxidized. (strong oxidizing agents will cause other metals to be oxidized and itself to be reduced)

Write the two half reactions.

Reduction: Ag+(aq) + e— → Ag(s) E = +0.80 V

Oxidation: Zn2+(aq) + 2e— → Zn(s) E = — 0.76 V

Use the equation to calculate cell potential.

Ecell = Ered — Eoxid

Ecell = +0.80 V — (— 0.76 V) = +1.56 V

Practice

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