The work of balancing a chemical equation is in many ways a series of trials and errors. As a sample exercise, consider the equation given below. Does this represent a balanced chemical equation?
| | | | |
| N2 | + | H2 | | NH3 |
To determine whether this reaction is balanced you must first determine how many atoms of each type are on the reactant side (left-hand side) of the equation and how many atoms of each type are on the product side (right-hand side). In this example, you have two blue nitrogen atoms and two gray hydrogen atoms on the reactant side but only one nitrogen atom and three hydrogen atoms on the product side. For the purpose of balancing the equation we are not concerned what molecules these atoms are in, just the number of atoms of each type.
To balance this reaction, it is best to choose one kind of atom to balance initially. Let's choose nitrogen in this case. To obtain the same number of nitrogen atoms on the product side as on the reactant side requires multiplying the number of product NH3 molecules by two to give:
| | | |  |
| N2 | + | H2 | | 2NH3 |
As you can see above, once we know what the molecules are (N2, H2, and NH3 in this case) we cannot change them (only how many of them there are). The nitrogen atoms are now balanced, but there are 6 atoms of hydrogen on the product side and only 2 of them on the reactant side. The next step requires multiplying the number of hydrogen molecules by three to give:
| |  | | |
| N2 | + | 3H2 | | 2NH3 |
As a final step, make sure to go back and check whether you indeed have the same number of each type of atom on the reactant side as on the product side. In this example we have two nitrogen atoms and six hydrogen atoms on both sides of the equation. We now have a balanced chemical equation for this reaction.
