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Cell Potentials

Redox Equations and Cell Potentials

Video tutorial
Redox reactions are divided into individual equations for the oxidation and reduction processes separately. These are called "half equations":
  • In the oxidation process, a substance loses one or more electrons: "Loss of Electrons is Oxidation" (OIL)
  • In the reduction process, a substance gains one or more electrons: "Reduction Is Gain" (RIG)
In Galvanic cells (batteries), the two processes are physically separate and are connected only a wire and a salt bridge. The two reactions happen in separate containers (such as beakers) and the electrons travel from one to the other via the wire, providing the possibility of producing electrical energy for us to use. The two processes together make the Galvanic cell and each is called a "half cell". In fact, the two half cells can be two different parts of an enzyme and the wire then becomes the atoms that connect them in the biomolecule.

Each half cell has a characteristic ability to give or take electrons. This is called its cell potential. The voltage (or potential) of the whole cell depends on the half cell potentials.

Redox reactions always involve an oxidation half cell and a reduction half cell: the electrons produced by the oxidation have to be used by a simultaneous reduction and the electrons required by the reduction have to come from an oxidation.

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