Balancing Redox Reactions

There are many methods to balance redox reactions, but it is best to pick a method and approach it systematically.

Here, one method (the half reaction method) will be presented.  If another methods works better for you, then great.  If not, learn this one and practice it.  An important idea is that balancing Redox reaction is different in acidic versus basic conditions.  This is because the reaction involves either H⁺ or OH^-  which will affect both the elements and the charge.

Here is the half reaction method in acidic solutions.

Step 1: Determine the oxidation numbers of the elements in the reaction and identify the oxidation and reduction reactions.

Step 2: Identify the oxidation and reduction half reactions and write the equations for each.

Step 3: For each half-reaction, balance all elements except for hydrogen and oxygen.  Then balance the oxygen by adding H₂O.  Then balance the hydrogen using H⁺.  Finally balance the charge in the half-reaction using electrons.

Step 4: Multiply one or both of the balanced half-reaction by whole numbers to equalize the number of the electrons in each half-reaction.

Step 5: Double check that all the elements and charge are balanced.

The half reaction method in basic conditions is nearly identical.  The steps are the same up through step 5.

Step 6: We now have a balanced equation except it has H⁺ and we want to get to basic conditions.  So now, add enough OH^- to each side of the equations to neutralize away any H⁺.  One side of the equation should now have the same number of H⁺ and OH^-.  These form water, H₂O molecules.  Now, cancel out any waters that appear on both sides of the equation.

Step 7: Double check that all elements and charge are balanced.