Chemical Reactions and Equations is the first Science chapter and gives 3–5 marks every year — usually ‘identify the type of reaction’ or ‘balance and name’.
Balancing in 4 steps
- Write the skeleton equation with correct formulas.
- Count atoms of each element on both sides.
- Balance the element that appears in the fewest compounds first; balance H and O last.
- Write physical states: (s), (l), (g), (aq).
Example
Fe + H₂O → Fe₃O₄ + H₂. Fe: 3Fe. O: 4H₂O. H: 8 → 4H₂. Final: 3Fe + 4H₂O → Fe₃O₄ + 4H₂.
Types of reactions
| Type | Pattern | Example |
|---|---|---|
| Combination | A + B → AB | CaO + H₂O → Ca(OH)₂ (exothermic) |
| Decomposition | AB → A + B | 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃ (thermal); 2AgCl → 2Ag + Cl₂ (photo) |
| Displacement | A + BC → AC + B | Fe + CuSO₄ → FeSO₄ + Cu |
| Double displacement | AB + CD → AD + CB | Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl (precipitation) |
| Redox | Oxidation + reduction | ZnO + C → Zn + CO (ZnO reduced, C oxidised) |
Key definitions
- Oxidation: gain of O or loss of H; Reduction: loss of O or gain of H.
- Exothermic: releases heat (respiration, burning); endothermic: absorbs heat (decomposition).
- Corrosion: rusting of iron (Fe₂O₃·xH₂O), black silver, green copper.
- Rancidity: oxidation of fats/oils; prevented by antioxidants, nitrogen flushing, refrigeration.
Board favourites
- Why is a magnesium ribbon cleaned before burning? — to remove the MgO layer.
- Why is respiration exothermic?
- White silver chloride turns grey in sunlight — photolytic decomposition.
Common mistakes
- Changing subscripts to balance (only coefficients can change)
- Calling a displacement reaction a double displacement
- Forgetting the ↑ and ↓ symbols for gas and precipitate
Related: Light Class 10 notes.
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Frequently asked questions
Are these Chemical Reactions and Equations Class 10 Notes notes enough for the exam?
They cover every formula, definition and question type that appears in school and board papers for this chapter. Use them with the NCERT examples, exercise questions and the last five years' papers to be fully prepared.
How should I revise Chemical Reactions and Equations Class 10 Notes?
Revise the notes after 1 day, 7 days and 30 days. Solve five questions each time instead of only reading, and keep an error list of the steps you get wrong.
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