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Balancing equations questions and answers

A balanced equation has the same number of each type of atom on both sides, because atoms aren't made or destroyed. You balance by changing the numbers in front of formulae, never the small numbers inside them. Type the balancing numbers in order (use 1 where there's no number).

8 questions · Foundation tier · Every answer is checked as you type it, with a full worked solution. Updated .

Start the questions Balancing equations guide Chemical equation balancer

Where balancing equations comes up

GCSE (AQA)Chemistry and Combined Science, Foundation and Higher: write and balance symbol equations. Higher only: balance an equation from the masses of reactants and products using moles.
Cambridge IGCSE (0620)Core: construct word and symbol equations with state symbols. Supplement: ionic equations, and deduce a balanced equation from information given.

The method

  1. Count the atoms of each element on both sides.
  2. Balance elements that appear in only one substance on each side first; leave elements on their own (like O₂ or H₂) until last.
  3. Change only the big numbers in front of formulae.
  4. Check every element again at the end.

Balancing equations questions

Try each one before looking at the hint. If you're stuck, the AI tutor can talk you through it step by step.

Warm-up

Question 1Warm-upFoundation

Balance: _ H2+_ O2→_ H2O\_\ \text{H}_2 + \_\ \text{O}_2 \rightarrow \_\ \text{H}_2\text{O}

Question 2Warm-upFoundation

Balance: _ Mg+_ O2→_ MgO\_\ \text{Mg} + \_\ \text{O}_2 \rightarrow \_\ \text{MgO}

Exam-style

Question 3Exam-styleFoundation

Balance: _ Na+_ Cl2→_ NaCl\_\ \text{Na} + \_\ \text{Cl}_2 \rightarrow \_\ \text{NaCl}

Question 4Exam-styleFoundation

Balance: _ N2+_ H2→_ NH3\_\ \text{N}_2 + \_\ \text{H}_2 \rightarrow \_\ \text{NH}_3

Question 5Exam-styleFoundation

Balance: _ CH4+_ O2→_ CO2+_ H2O\_\ \text{CH}_4 + \_\ \text{O}_2 \rightarrow \_\ \text{CO}_2 + \_\ \text{H}_2\text{O}

Question 6Exam-styleFoundation

Balance: _ Mg+_ HCl→_ MgCl2+_ H2\_\ \text{Mg} + \_\ \text{HCl} \rightarrow \_\ \text{MgCl}_2 + \_\ \text{H}_2

Challenge

Question 7ChallengeFoundation

Balance: _ Fe2O3+_ CO→_ Fe+_ CO2\_\ \text{Fe}_2\text{O}_3 + \_\ \text{CO} \rightarrow \_\ \text{Fe} + \_\ \text{CO}_2

Question 8ChallengeFoundation

Balance: _ C3H8+_ O2→_ CO2+_ H2O\_\ \text{C}_3\text{H}_8 + \_\ \text{O}_2 \rightarrow \_\ \text{CO}_2 + \_\ \text{H}_2\text{O}

Common mistakes

  • Changing a formula's small numbers (e.g. H₂O to H₂O₂).
  • Forgetting that a number in front multiplies every atom in the formula.
  • Not rechecking after a change.

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Sources

The questions are our own. The “where it comes up” notes are from each board's published specification, checked on 27 October 2026:

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