A chemical reaction can be expressed as an equation.
A chemical equation shows the chemicals that react (the reactants) followed by an arrow followed by the chemicals that are produced by the reaction (the products).
Here is an example of a chemical equation: Al + O2 --> Al2O3.
Chemical equations must be balanced since anything that is consumed by the reaction must form product – we can’t have atoms disappearing or appearing out of nowhere!
To balance an equation: we add a coefficient to the front of each element or compound that requires it. Essentially you are multiplying the amount of atoms or compounds on one side to match the amount on the other side.
Let’s try an example! We will take the given equation: Al + O2 --> Al2O3. We can see that this is not balanced – there is 1 aluminum on the reactant side and 2 on the product side, and there are 2 oxygens on the reactant side and 3 on the product side. How will we balance it?
First, let’s multiply the aluminum on the reactant side by 2 to match the amount of aluminum on the products side. Then we have to deal with the oxygens. There are 2 on the reactant side and 3 on the product side – since neither one is a multiple of the other, the best thing to do is find the least common multiple of both of them. This would be 6. (2 x 3 = 6). We can then adjust each side to have 6 oxygens by putting a coefficient of 3 in front of the diatomic reactant oxygen and a 2 in front of the compound on the product side.
Now, however, we see that there are 4 aluminums on the product side, so again we need to adjust the reactant aluminum! We can then change the coefficient of 2 in front of the aluminum to a 4.
Finally we have a balanced equation: 4Al + 3O2 --> 2Al2O3 . There 4 aluminums on each side and 6 oxygens on each side!