Quick answer: A balanced chemical equation has the same number of atoms of each element on both sides. Change coefficients in front of formulas; changing subscripts changes the substances.
Worked example
Balance Fe + O₂ → Fe₂O₃.
- Oxygen occurs in groups of 2 and 3; their least common multiple is 6.
- Use 3O₂ and 2Fe₂O₃ to give six oxygen atoms on each side.
- The products now contain four iron atoms, so put 4 before Fe.
- Balanced equation: 4Fe + 3O₂ → 2Fe₂O₃.
Check the result
Left: Fe 4, O 6. Right: Fe 2×2 = 4, O 2×3 = 6. Coefficients have no common factor greater than 1.
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Common mistake to avoid
Never change Fe₂O₃ to another formula to balance atoms. The arrow states a reaction; balancing alone does not specify conditions or prove that it occurs.
Try it yourself
1. Balance H₂ + O₂ → H₂O. 2. Balance N₂ + H₂ → NH₃.
Answers and reasoning
1. 2H₂ + O₂ → 2H₂O. 2. N₂ + 3H₂ → 2NH₃. Check each element separately.
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