Balancing simple Oxidation- Reduction by half-reaction method

Oxidation - reduction reactions can often be quite difficult to balance. The Half-reaction method is quite useful in balancing it. It consists of first separating the equation into two half reactions, one for oxidation and other for reduction. You balance each half- reaction ,  then combine them to obtain a balanced oxidation-reduction reaction. First we identify the species being oxidized and reduced and assign the appropriate oxidation states.

             

                                           Zn(s) + Ag⁺(aq) -> Zn²⁺ (s) + Ag(aq)

Now write the half -reactions in an unbalanced form:

                                              Zn  -> Zn²⁺    (oxidation)

                                              Ag⁺ -> Ag     (reduction)

Now , balance the charge in each equation by adding electrons to the more positive side to create balanced half-reactions. Following this procedure, the balanced half reactions are:

                                             Zn -> Zn²⁺ + 2 e^-  (Oxidation half reaction)

                                            Ag⁺ + e^- -> Ag      (Reduction half reaction)

To meet the goal and obtain the balanced oxidation -reduction, we multiply each half reaction by a factor(integer) so that we can add them together, the electrons cancel.

                                          1 X (  Zn -> Zn²⁺ + 2 e^- )

                                    2 X(  Ag⁺ + e^- -> Ag )

                                 -------------------------------------

                                Zn + 2 Ag⁺+ 2e-  -> .Zn²⁺ + 2Ag + 2 e-

       Thus the final equation after balancing is : Zn + 2 Ag⁺ -> .Zn²⁺ + 2Ag