Steps for Balancing Redox Reactions by Oxidation Number
1. Write above each element its oxidation number.
2. With the "line method", show the oxidation before & after reaction.
3. Then write how many electrons are moving for the oxidizing element and reducing element.
4. Change the coefficient in front of the species until the # of electrons gaining/losing (i.e. transferring) are equal.
5. Important note: this number of electrons moving is for one element, so if you have two, three, etc of these elements in the species chemical formula, you must multiply by that number to determine the number of electrons moving. Then you change the coefficient. At this point, you are only looking at the reactants, never the products.
6. Balance the rest by atoms (even if you have to change the coefficient from the electron balancing).