How to balance chemical equations
Step-by-step method for balancing equations, with worked examples.
Why we balance
Atoms are never created or destroyed in a reaction (conservation of mass), so there must be the same number of each type of atom on both sides of the equation.
The method
1. Write the correct formulas. 2. Count the atoms of each element on each side. 3. Add big numbers (coefficients) in front of formulas, never change the small numbers. 4. Recount until every element balances.
Top tip
Balance elements that appear in only one substance on each side first, and leave hydrogen and oxygen until last.
✏️ Worked example
Balance: CH₄ + O₂ → CO₂ + H₂O
Carbon: 1 and 1, fine. Hydrogen: 4 on the left, so put 2 in front of H₂O. Oxygen: now 2 + 2 = 4 on the right, so put 2 in front of O₂. CH₄ + 2O₂ → CO₂ + 2H₂O.
🧠 Test yourself
Balance: H₂ + O₂ → H₂O
2H₂ + O₂ → 2H₂O
Balance: Mg + HCl → MgCl₂ + H₂
Mg + 2HCl → MgCl₂ + H₂
Why can't you change H₂O to H₂O₂ to balance it?
That would make a different substance (hydrogen peroxide).
Want it to stick?
Practise with quizzes, an AI study helper and a Mistake Bank that brings back what you got wrong, all free on OmniEx.
Revise this on OmniEx →