Here is an example. Consider the oxidation of propane.
| __ C3H8 + __O2 --> __CO2 + __H2O |
The most complexe coumpund is propane. The carbon atoms will balance if the coefficient on carbon dioxide is 3.
| __ C3H8 + __O2 --> 3 CO2 + __H2O |
Next, the hydrogens will balance if the coefficient on water is 4.
| __ C3H8 + __O2 --> 3 CO2 + 4 H2O |
No there are 10 oxygen atoms depicted on the products side of the reation so the coefficient on oxygen (on the reactants side) must be 5.
| __ C3H8 + 5 O2 --> 3 CO2 + 4 H2O |
These numbers were chosen assuming the coefficient on propane was 1.
| 1 C3H8 + 5 O2 --> 3 CO2 + 4 H2O |
So the final balanced reaction equation is:
| C3H8 + 5 O2 --> 3 CO2 + 4 H2O |
The sum of the coefficients of the reactants and the products in this reaction is 13.
Note: A properly balanced reaction equation will always use the smallest whole numbers which are possible. Thus, while a reaction such as
is technically balanced, it is only properly balanced as
since this equation contains no fractions.
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Department of Chemistry and Biochemistry
California State University, East Bay
patrick.fleming@csueastbay.edu