Last Updated: April 2026
Chemical Reactions and Equations is Chapter 1 of CBSE Class 10 Science (Chemistry). In CBSE Board 2025, this chapter contributed 5-7 marks in the Science paper. Understanding how to write and balance chemical equations, identify reaction types, and recall key reactions is essential for scoring full marks in this chapter.
Chapter Summary — Chemical Reactions and Equations
A chemical reaction involves the conversion of reactants into products with a change in chemical properties. Chemical equations represent reactions using symbols and formulas. Balanced equations satisfy the Law of Conservation of Mass.
Types of Chemical Reactions — CBSE Class 10
| Reaction Type | Definition | Example |
|---|---|---|
| Combination Reaction | Two or more substances combine to form a single product | 2Mg + O2 → 2MgO |
| Decomposition Reaction | Single compound breaks into two or more simpler products | 2H2O → 2H2 + O2 (electrolysis) |
| Displacement Reaction | More reactive element displaces less reactive element | Fe + CuSO4 → FeSO4 + Cu |
| Double Displacement | Exchange of ions between two compounds | Na2SO4 + BaCl2 → BaSO4 + 2NaCl |
| Oxidation-Reduction (Redox) | Simultaneous oxidation and reduction | CuO + H2 → Cu + H2O |
| Exothermic Reaction | Releases heat energy | Natural gas combustion, respiration |
| Endothermic Reaction | Absorbs heat energy | Photosynthesis, decomposition of calcium carbonate |
Key Chemical Equations for CBSE Board 2026
| Reaction | Equation | Type |
|---|---|---|
| Burning of magnesium | 2Mg + O2 → 2MgO | Combination, Exothermic |
| Electrolysis of water | 2H2O → 2H2 + O2 | Decomposition |
| Thermal decomposition of lead nitrate | 2Pb(NO3)2 → 2PbO + 4NO2 + O2 | Decomposition |
| Iron with copper sulphate | Fe + CuSO4 → FeSO4 + Cu | Displacement |
| Silver nitrate + sodium chloride | AgNO3 + NaCl → AgCl + NaNO3 | Double Displacement (precipitation) |
| Calcium carbonate heating | CaCO3 → CaO + CO2 | Decomposition (thermal) |
| Quick lime + water | CaO + H2O → Ca(OH)2 | Combination, Exothermic |
How to Balance Chemical Equations — Step-by-Step Method
- Write the unbalanced equation with correct formulas for all reactants and products
- Count atoms of each element on both sides
- Add coefficients (whole numbers) to balance atoms — start with the most complex molecule
- Balance metals first, then non-metals, leave hydrogen and oxygen for last
- Check: total atoms of each element must be equal on both sides
- Verify that all coefficients are the smallest possible whole numbers
CBSE Class 10 Important Questions — Chemical Reactions
- Why should magnesium ribbon be cleaned before burning in air? (Ans: To remove the oxide layer which would prevent burning)
- What happens when zinc is added to ferrous sulphate solution? Write the equation. (Ans: Zn is more reactive than Fe — displacement reaction: Zn + FeSO4 → ZnSO4 + Fe)
- Define corrosion with an example. How can it be prevented? (Ans: Gradual deterioration of metals — rusting of iron; prevented by painting, galvanising, alloying)
- What is rancidity? How is it related to oxidation? (Ans: Oxidation of fats and oils making food smell bad — prevented by adding antioxidants, vacuum packing)
- What happens when silver chloride is exposed to sunlight? (Ans: Photodecomposition — 2AgCl → 2Ag + Cl2; used in black and white photography)
Frequently Asked Questions — CBSE Class 10 Chemical Reactions
How many types of chemical reactions are in CBSE Class 10?
CBSE Class 10 Science Chapter 1 covers 5 main types of chemical reactions: Combination, Decomposition, Displacement, Double Displacement, and Oxidation-Reduction (Redox). Reactions can also be classified as Exothermic (heat releasing) or Endothermic (heat absorbing). Understanding each type with examples is essential for CBSE board exams.
What is the Law of Conservation of Mass?
The Law of Conservation of Mass states that mass can neither be created nor destroyed in a chemical reaction. The total mass of reactants equals the total mass of products. This is why chemical equations must be balanced — the number of atoms of each element must be equal on both sides of the equation.
What is the difference between corrosion and rancidity?
Corrosion is the oxidation of metals by atmospheric oxygen and moisture — for example, rusting of iron (Fe2O3.xH2O). Rancidity is the oxidation of fats and oils in food, producing unpleasant smell and taste. Both are oxidation processes but corrosion affects metals while rancidity affects food containing fat. Both can be prevented by limiting exposure to oxygen.
How many marks does Chapter 1 carry in CBSE Class 10 Science board exam?
Chemical Reactions and Equations typically contributes 5-7 marks in the CBSE Class 10 Science board examination. Questions can be 1-mark (definition/MCQ), 2-mark (short answer), 3-mark (balanced equations), and 5-mark (long answer covering multiple reaction types with equations). Mastering this chapter fully ensures full marks from these questions.
Get NCERT solutions and chapter-wise practice tests for CBSE Class 10 and 12 at Ready For Boards.
