Definition of Redox reactions (balancing)

  • Balance the atoms being oxidized or reduced.
  • Balance oxidation numbers by adding electrons.
  • Balance charge by adding H+ (acidic solutions) or OH- (basic solutions).
  • Balance H atoms by adding H2O. Balancing Redox Reactions
  • Write the half reactions.
  • Balance each half reaction.
  • Combine the half reactions to eliminate the electrons from the overall reaction. Example

    Fe2+(aq) + MnO4-(aq) ---> Fe3+(aq) + Mn2+(aq) (acidic solution)

    1. Write the half reactions:

    Fe2+(aq) ---> Fe3+(aq) (oxidation)

    MnO4-(aq) ---> Mn2+(aq) (reduction)

    2. Balance each half reaction:

    Fe2+(aq) ---> Fe3+(aq) + e-

    MnO4-(aq) + 8H+(aq) + 5e- ---> Mn2+(aq) + 4H2O

    3. Combine the half reactions to give the overall reaction: 5Fe2+(aq) ---> 5Fe3+(aq) + 5e- MnO4-(aq) + 8H+(aq) + 5e- ---> Mn2+(aq) + 4H2O ------------------------------------------------------------ 5Fe2+(aq) + MnO4-(aq) + 8H+(aq) ---> 5Fe3+(aq) + Mn2+(aq) + 4H2O

    Try balancing the lead-acid battery reaction:

    Pb(s) + PbO2 (s) + SO42-(aq) ---> PbSO4(s)






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