Balancing Chemical Equations

Let’s look at how to balance a chemical equation correctly, using the following reaction as an example:

Al + O₂ → Al₂O₃

1. Count the Number of Each Element on Both Sides.

Start with metals and non-metals, leaving oxygen and hydrogen for last if present.

Reactants	Element	Product
1	Al	2
2	O	3

We have an imbalance of Al atoms, as there’s 1 atom in the reactants and 2 in the products.

2. Balance Aluminium (Al).

Place a coefficient of 2 before Al in the reactants to equalise the aluminium atoms on both sides.

Reactants	Element	Product
2 × 1	Al	2
2	O	3

2Al + O₂ → Al₂O₃

3. Balance Oxygen (O).

Initially, there are 2 oxygen atoms in the reactants and 3 in the products. Multiplying the oxygen in the reactants by 3 and in the products by 2 gives us 6 oxygens on each side.

Reactants	Element	Product
2 × 1	Al	2 × 2
3 × 2	O	2 × 3

2Al + 3O₂ → 2Al₂O₃

Now, because we altered the balance for oxygen, recheck aluminium again:

To maintain balance, we now need 4 Al atoms in the reactants.

Reactants	Element	Product
2 × 2 × 1 = 4	Al	2 × 2
3 × 2	O	2 × 3

4Al + 3O₂ → 2Al₂O₃

4. Final Check.

Ensure the atoms are balanced across reactants and products.

Reactants	Element	Product
4	Al	4
6	O	6

4Al + 3O₂ → 2Al₂O₃

Both sides have 4 aluminium atoms and 6 oxygen atoms.