The standard reduction potential, designated by E¬°cell, of a substance is the ease with which it accepts electrons and is reduced. When two substances are placed in an electrochemical cell, the substance with the more positive reduction potential serves as the cathode. Reduction potentials are also used to calculate the electromotive force (emf) of a cell. The emf or cell potential is given by
The oxidation potential of the oxidized substance is added to the reduction potential of the reduced substance. If you are given the reduction potential for a certain process, the oxidation potential is equal in magnitude but opposite in sign. A spontaneous galvanic cell has a positive emf and a non-spontaneous galvanic cell has a negative emf.
Example:
Determine the cell potential of the following galvanic cell: one beaker has solid magnesium in an aqueous solution of magnesium sulfate, the other beaker has solid lead in an aqueous solution of lead sulfate. E¬° Mg=-2.372V, E¬° Pb=-.126V.
