20 Important Balanced Chemical Equations

1. Formation of water: 2H₂ + O₂ → 2H₂O

2. Formation of ammonia: N₂ + 3H₂ → 2NH₃

3. Burning of magnesium: 2Mg + O₂ → 2MgO

4. Formation of calcium oxide (quicklime): 2Ca + O₂ → 2CaO

5. Iron rusting (simplified): 4Fe + 3O₂ → 2Fe₂O₃

6. Electrolysis of water: 2H₂O → 2H₂ + O₂

7. Decomposition of calcium carbonate (limestone): CaCO₃ → CaO + CO₂

8. Decomposition of silver chloride (in sunlight): 2AgCl → 2Ag + Cl₂

9. Decomposition of ferrous sulphate: 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃

10. Decomposition of lead nitrate: 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂

11. Zinc displaces copper: Zn + CuSO₄ → ZnSO₄ + Cu

12. Iron displaces copper: Fe + CuSO₄ → FeSO₄ + Cu

13. Sodium in water: 2Na + 2H₂O → 2NaOH + H₂

14. Zinc with dilute H₂SO₄: Zn + H₂SO₄ → ZnSO₄ + H₂

15. Magnesium with HCl: Mg + 2HCl → MgCl₂ + H₂

16. Neutralisation (NaOH + HCl): NaOH + HCl → NaCl + H₂O

17. Precipitation (silver nitrate + sodium chloride): AgNO₃ + NaCl → AgCl↓ + NaNO₃

18. Combustion of methane: CH₄ + 2O₂ → CO₂ + 2H₂O

19. Combustion of ethanol: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

20. Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Steps:

1. Write the unbalanced equation with correct formulae
2. Count atoms on each side
3. Add coefficients (whole numbers) to balance — never change subscripts!
4. Start with the most complex molecule
5. Balance metals first, then non-metals, hydrogen last, oxygen last

Example: Balance H₂ + O₂ → H₂O

• Left: 2H, 2O → Right: 2H, 1O (unbalanced O)
• Add coefficient 2 on right: H₂ + O₂ → 2H₂O
• Now left needs 2H₂: 2H₂ + O₂ → 2H₂O ✓