In a galvanic cell, a spontaneous redox reaction occurs. however, the reactants are separated such that the transfer of electrons is forced to occur across a wire. the resulting electricity is measured in volts (v and is the sum of the potentials of the oxidation and reduction half-reactions:

Oxidation is the loss of electrons and corresponds to an increase in oxidation state. Reduction is the gain of electrons and corresponds to a decrease in oxidation state. Balancing redox reactions can be more complicated than balancing other types of reactions because both the mass and charge must be balanced. Redox reactions occurring in aqueous solutions can be balanced by using a special procedure called the half-reaction method of balancing. In this procedure the overall equation is broken down into two half-reactions: one for oxidation and the other for reduction. The half-reactions are balanced individually and then added together so that the number of electrons generated in the oxidation half reaction is the same as the number of electrons consumed in the reduction half-reaction.