There is another useful method for balancing redox equations: the half-reaction method. In this method each substance that changes its oxidation number is balanced separately in a half-reaction that includes electrons explicitly. The two balanced half-reactions then are combined in such a way as to cancel electrons from the final expression.

Example.
Balance the iron and permanganate reaction by the half-reaction method.

Solution.
The unbalanced permanganate half-reaction is




Five electrons were needed because manganese goes from +7 to +2 oxidation state. Water molecules are added on the right to balance the oxygen atoms in the permanganate, and protons are added to the left:



This half-reaction is now balanced with respect to both number of atoms and overall charge, +2 on each side.