Balancing step by step
Let us now balance the reaction between magnesium and oxygen step by step.
The starting point
Mg + O2 → MgO
The formulae are right, but it is not yet balanced.
Step 1 — evening up the oxygen
There are two oxygen atoms in the reactants and one in the products.
We cannot write MgO2 to even up the oxygen — the formula is MgO. So we put a 2 in front of MgO.
Mg + O2 → 2MgO
Step 2 — evening up the magnesium
Writing "2MgO" puts two magnesium atoms on the product side.
The reactant side has only one magnesium atom, so a 2 must go in front of Mg as well.
2Mg + O2 → 2MgO
This is the balanced equation for the reaction between magnesium and oxygen.
Let us check it
| Atom | In the reactants | In the products |
|---|---|---|
| Mg | 2 | 2 |
| O | 2 | 2 |
Always count at the end
Once balanced, count the atoms of each element and confirm the two sides agree. It takes a few seconds and it catches mistakes.