Chemical Reactions and Equations – Class 10 SSC Science 1 (Chapter 3)
Simple, exam-focused notes with examples, balancing steps, study tips and FAQs. Perfect for last‑minute revision.
Introduction
Chemical reactions power our world—from rusting iron to charging batteries and cooking food. In Chapter 3 of Class 10 SSC Science 1, you’ll learn how to represent these changes using chemical equations, classify reaction types, and balance equations according to the Law of Conservation of Mass.
What is a Chemical Reaction?
A chemical reaction is a process where one or more substances (reactants) convert into new substances (products) with different properties by rearrangement of atoms.
Example: Burning magnesium ribbon
Mg + O2 → 2MgO
Writing Chemical Equations
Steps
- Write the word equation (reactants → products).
- Replace words with formulae.
- Balance atoms on both sides.
- Add state symbols (s, l, g, aq) if needed.
- Include conditions (heat, catalyst) above/below the arrow.
Illustration
Fe + S → FeS
2H2 + O2 → 2H2O
Types of Chemical Reactions
1) Combination
Two or more substances combine to form one product.
CaO + H2O → Ca(OH)2
2) Decomposition
One compound breaks into simpler substances (often on heating or electrolysis).
2KClO3 → 2KCl + 3O2
3) Displacement
More reactive element displaces a less reactive one from its compound.
Zn + CuSO4 → ZnSO4 + Cu
4) Double Displacement
Exchange of ions between two compounds, often forming a precipitate.
AgNO3 + NaCl → AgCl ↓ + NaNO3
5) Redox
Oxidation and reduction occur simultaneously.
CuO + H2 → Cu + H2O
Oxidation & Reduction (Redox)
Oxidation
Gain of oxygen / loss of hydrogen / loss of electrons.
2Mg + O2 → 2MgO (Mg oxidized)
Reduction
Loss of oxygen / gain of hydrogen / gain of electrons.
CuO + H2 → Cu + H2O (CuO reduced)
Agents: Oxidizing agent causes oxidation (and gets reduced). Reducing agent causes reduction (and gets oxidized).
Real‑Life Applications: Corrosion & Rancidity
Corrosion (Rusting)
Iron reacts with oxygen and moisture forming rust. Prevention: painting, galvanizing, oiling/greasing.
Rancidity
Oxidation of fats/oils produces unpleasant smell/taste. Prevention: airtight containers, antioxidants, refrigeration, nitrogen packing.
Quick Practice
Balance the following:
- __ Al + __ O2 → __ Al2O3
- __ Na + __ H2O → __ NaOH + __ H2
- __ CaCO3 → __ CaO + __ CO2
- __ FeCl3 + __ NH4OH → __ Fe(OH)3 + __ NH4Cl
Answers: 4Al + 3O2 → 2Al2O3; 2Na + 2H2O → 2NaOH + H2; CaCO3 → CaO + CO2; FeCl3 + 3NH4OH → Fe(OH)3 + 3NH4Cl.
Study Tips (Score Booster)
- Memorise key definitions: oxidation, reduction, displacement, precipitate.
- Practise balancing 10 equations daily—time yourself (max 10 minutes).
- Make a one‑page formula sheet with 2 examples per reaction type.
- Revise previous years’ SSC questions from this chapter.
- Use colour codes in your notebook: reactants (blue), products (green), conditions (orange).
FAQs: Chemical Reactions & Equations
Why is balancing a chemical equation important?
It satisfies the Law of Conservation of Mass—atoms are neither created nor destroyed, so the count of each element must match on both sides.
Which reactions give a precipitate?
Many double displacement reactions form an insoluble salt (precipitate), e.g., AgNO3 + NaCl → AgCl ↓ + NaNO3.
Is photosynthesis a combination reaction?
Yes. CO2 and H2O combine in the presence of sunlight and chlorophyll to form glucose and O2.
How do I identify oxidation and reduction quickly?
Track oxygen and hydrogen: gain of O or loss of H is oxidation; loss of O or gain of H is reduction. In redox, both occur together.
How many marks does this chapter usually carry?
Weightage varies by paper, but you can expect balancing/identification and short concept questions (2–4 marks). Always check the latest blueprint.
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📚 Also Read:
- Download 11th HSC Chemistry Textbook PDF – Maharashtra Board Free (2025)
- Identify the Type of Chemical Reaction – 20 Practice Questions for Class 10
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