The Half-Reaction Method

In the half-reaction method what we do is first break an equation into two parts and then balance the parts individually. Presented stepwise:

• Separate the reaction into two half-reactions.
• Balance each half-reaction separately:
  1. Balance atoms other than O & H by inspection.
  2. Balance O by adding H₂O to the opposite side.
  3. Balance H:
     • In acid solution add H⁺ as appropriate.
     • In base solution add H₂O to the side needing H, balance O by adding equal numbers of OH^- to the opposite side.
  4. Balance the charge by adding electrons (e^-) - add to same side as excess of positive charge, or opposite side if excess negative charge.
• Balance the charges of the two half-reactions by multiplying appropriately, then add to two equations together and cancel items appearing on both sides.

© R A Paselk

Last modified 27 October 2008