Download BALANCING REDOX EQUATIONS

BALANCING REDOX EQUATIONS
Honors Chemistry
Two Methods:
1.) Oxidation-Number Changes – comparing the increase/decrease in
oxidation number
2.) Half-Reactions – balance half-reactions separately
Oxidation Number Changes
1. Start with skeleton equation (unbalanced).
2. Assign oxidation numbers to all the atoms in the equation. Write the
number above the atoms.
3. Identify which atoms are oxidized and which are reduced.
4. Use the “arrow” method to connect the atoms that undergo
oxidation and reduction and write the number of electrons
lost/gained.
5. Make the total increase in oxidation number equal to the total
decrease on oxidation number by using appropriate coefficients.
6. Self-check to make sure the equation is balanced for both atoms
and charge.
EX.
Fe2O3(s) + CO(g)  Fe(s) + CO2(g)
Half-Reactions
1. Start with the skeleton equation (unbalanced).
2. Write the unbalanced equation in ionic form (separate all (aq)
species).
3. Write separate half-reactions for the oxidation and reduction
processes.
4. Balance the atoms in the half-reactions
a. To balance oxygen, add enough H2O molecules to balance
the half-reaction.
b. To balance Hydrogen (from the water or other sources) add
H+(aq).
5. Add enough electrons to one side of each half-reaction to balance
the charges. (**Remember electrons carry a negative charge)
6. Multiply each half-reaction by a coefficient to make the number of
electrons equal in both oxidation and reduction reactions.
7. Add the balanced half-reactions to show an overall equation and
subtract terms that appear on both sides of the equation.
EX:
S(s) + HNO3(aq)  SO2(g) + NO(g) + H2O(l)