22.3. Balancing Redox Reactions http://www.ck12.org
The carbon atom’s oxidation number increases by 2, while the iron atom’s oxidation number decreases by 3. As
written, the number of electrons lost does not equal the number of electrons gained. In a balanced redox equation,
these values must be equal, so coefficients must be used to make the total increase in oxidation number for all atoms
equal to the total decrease in oxidation number for all atoms.
Step 4: Use coefficients to make the total increase in oxidation number equal to the total decrease in oxidation
number. In this case, the least common multiple of 2 and 3 is 6. So the oxidation-number increase should be
multiplied by 3, while the oxidation-number decrease should be multiplied by 2. These coefficients are applied to
the corresponding formulas in the equation. A 3 is placed in front of CO and CO 2 , while a 2 is placed in front of Fe
on the right side of the equation. The Fe 2 O 3 does not require a coefficient because the subscript of 2 indicates that
there are already two iron atoms.
Step 5: Check to see if the equation is balanced in terms of both atoms and charge. Occasionally, a coefficient
may need to be placed in front of a formula that was not involved in the redox process. In the current example, the
equation is now balanced.
Fe 2 O 3 (s)+3CO(g)→2Fe(s)+3CO 2 (g)FIGURE 22.6
A blast furnace is where iron ore is pro-
cessed and turned into iron metal. First,
air is blown through a mixture of iron ore
and coke (carbon). The carbon monoxide
produced reduces the Fe^3 +ions in the
iron ore to metallic iron.Half-Reaction Method
Another method for balancing redox reactions uses half-reactions. Recall that half-reactions treat oxidation and
reduction as two separate processes that are occurring simultaneously. The half-reaction method tends to work