Advanced Study Material for Class 10 Science: Chapter 01 Chemical Reactions and Equations
Access comprehensive study materials and useful resources for Chapter 01 Chemical Reactions and Equations using the CBSE Class 10 Science Chemical Reactions and Equations Important Questions with Answers Set 01. Designed to align with the 2026-27 CBSE academic guidelines, these advanced resources help Class 10 Science students reinforce core concepts beyond standard textbooks.
Practice Class 10 Science Resources: Chapter 01 Chemical Reactions and Equations
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Very Short Answer Questions
1. State one industrial application of the reduction process.
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Answer: It is used in metallurgical processes for the refining of metals.
Teacher's Note: Use the key term in your answer.
2. Which is a chemical change: rusting of iron or melting of iron?
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Answer: Rusting of iron.
Teacher's Note: Give an example if the question allows.
3. State one basic difference between a physical change and a chemical change.
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Answer: In a physical change no new substance is formed; in a chemical change a new substance is formed.
Teacher's Note: Write a short, clear answer.
4. Which is a chemical change: fermentation of fruit juice or diluting fruit juice?
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Answer: Fermentation of fruit juice.
Teacher's Note: Remember this for your exam.
5. Which is a chemical change: burning of wax or melting of wax? Give the reason.
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Answer: Burning of wax. Candle wax is a hydrocarbon that burns to give CO2 and H2O, and the change is irreversible.
Teacher's Note: Learn this point and write it in your own words.
6. If copper is heated over a flame it develops a coating. What are its colour and composition?
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Answer: Black, copper(II) oxide (CuO).
Teacher's Note: Use the key term in your answer.
7. All decomposition reactions are endothermic. Why?
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Answer: Energy in the form of heat, light or electricity is needed to break down the compound.
Teacher's Note: Give an example if the question allows.
8. In the electrolysis of water, why is the volume of gas at one electrode double that at the other?
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Answer: Water splits as 2H2O → 2H2 + O2, so hydrogen and oxygen are formed in the ratio 2 : 1 by volume.
Teacher's Note: Write a short, clear answer.
9. Which is a chemical change: electrolysis of water or sodium chloride exposed to sunlight?
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Answer: Electrolysis of water.
Teacher's Note: Remember this for your exam.
10. What is a skeletal equation?
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Answer: An unbalanced chemical equation.
Teacher's Note: Learn this point and write it in your own words.
11. On adding dilute hydrochloric acid to copper oxide powder the solution turns blue-green. Name the compound formed.
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Answer: Copper(II) chloride, CuCl2.
Teacher's Note: Use the key term in your answer.
12. What happens when quicklime is added to water?
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Answer: It reacts vigorously to form slaked lime with a lot of heat: CaO + H2O → Ca(OH)2 + heat.
Teacher's Note: Give an example if the question allows.
13. Balance: FeSO4 → Fe2O3 + SO2 + SO3 (on heating).
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Answer: 2FeSO4 → Fe2O3 + SO2 + SO3
Teacher's Note: Write a short, clear answer.
14. What happens when ZnCO3 is heated in the absence of air?
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Answer: Zinc oxide and carbon dioxide are formed: ZnCO3 → ZnO + CO2.
Teacher's Note: Remember this for your exam.
15. Name and state the law kept in mind while balancing a chemical equation.
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Answer: The law of conservation of mass: mass can neither be created nor destroyed in a chemical reaction.
Teacher's Note: Learn this point and write it in your own words.
16. Why are decomposition reactions called the opposite of combination reactions?
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Answer: In a combination reaction two or more substances join to form one; in a decomposition reaction one compound breaks into two or more substances.
Teacher's Note: Use the key term in your answer.
17. Name the reaction used to extract metals from their oxides or chlorides.
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Answer: Electrolytic reduction.
Teacher's Note: Give an example if the question allows.
18. Why is photosynthesis an endothermic reaction?
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Answer: Because it absorbs energy (sunlight).
Teacher's Note: Write a short, clear answer.
19. Why is hydrogen peroxide kept in coloured bottles?
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Answer: In sunlight it decomposes into water and oxygen (2H2O2 → 2H2O + O2); coloured bottles prevent this.
Teacher's Note: Remember this for your exam.
20. Name the type of reaction: N2 + 3H2 → 2NH3.
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Answer: A combination reaction.
Teacher's Note: Learn this point and write it in your own words.
21. Why should a magnesium ribbon be cleaned before burning in air?
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Answer: It is coated with a layer of magnesium oxide, which must be removed with sandpaper so the metal can burn.
Teacher's Note: Use the key term in your answer.
22. Why do we paint iron articles?
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Answer: To prevent rusting.
Teacher's Note: Give an example if the question allows.
23. Why are oil and fat containing foods flushed with nitrogen?
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Answer: Nitrogen prevents the food from being oxidised, so it can be kept for longer.
Teacher's Note: Write a short, clear answer.
Short Answer Questions
24. Hydrogen burns in oxygen to form water; water on electrolysis gives hydrogen and oxygen. State the kind of reaction in each case.
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Answer: The first is a combination reaction; the second is a decomposition reaction.
Teacher's Note: Remember this for your exam.
25. A green iron salt, when heated strongly, turns black and gives the smell of burning sulphur. Name the salt and the type of reaction.
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Answer: Ferrous sulphate (FeSO4); a decomposition reaction.
Teacher's Note: Learn this point and write it in your own words.
26. Hydrogen is passed over heated copper(II) oxide to give copper and steam. Write the equation and name the substance oxidised and reduced.
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Answer: CuO + H2 → Cu + H2O. H2 is oxidised and CuO is reduced.
Teacher's Note: Use the key term in your answer.
27. Give reasons: (i) Chips packets are filled with nitrogen. (ii) New iron articles shine but get a reddish-brown coating with time.
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Answer: (i) To prevent rancidity (oxidation of the oil). (ii) Iron rusts (corrodes) in moist air.
Teacher's Note: Give an example if the question allows.
28. Give two industrial uses of decomposition reactions with equations.
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Answer: (i) In making cement, quicklime is obtained by heating limestone: CaCO3 → CaO + CO2. (ii) In photochromic glass, silver halides decompose in sunlight: 2AgCl → 2Ag + Cl2.
Teacher's Note: Write a short, clear answer.
29. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
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Answer: Iron is more reactive than copper, so it displaces copper from the solution and forms green iron sulphate: Fe + CuSO4 → FeSO4 + Cu.
Teacher's Note: Remember this for your exam.
30. Metal X + salt solution of Y → salt solution of X + metal Y. What do you infer?
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Answer: It is a displacement reaction. X is more reactive than Y because it displaces Y from its salt solution.
Teacher's Note: Learn this point and write it in your own words.
31. Can oxidation or reduction take place alone? What are such reactions called?
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Answer: No. When one substance is oxidised another is reduced at the same time. Such reactions are redox reactions.
Teacher's Note: Use the key term in your answer.
32. Name the type of reaction: compost formation; burning of natural gas; silver turning black in air; colour change when an iron nail is put in copper sulphate.
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Answer: Decomposition; oxidation (combustion); oxidation (corrosion); displacement.
Teacher's Note: Give an example if the question allows.
33. An aluminium can stored ferrous sulphate solution and developed holes. Explain.
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Answer: Aluminium is more reactive than iron and displaces iron from ferrous sulphate, so the can is eaten away: 2Al + 3FeSO4 → Al2(SO4)3 + 3Fe.
Teacher's Note: Write a short, clear answer.
34. The smell and taste of fatty food change after some time. Name the process and give two ways to prevent it.
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Answer: Rancidity (oxidation of fats and oils). It can be prevented by storing food in airtight containers or a refrigerator, adding antioxidants, or flushing with nitrogen.
Teacher's Note: Remember this for your exam.
35. Identify the type: (i) CH4 + 2O2 → CO2 + 2H2O (ii) Pb(NO3)2 + 2KI → PbI2 + 2KNO3 (iii) CaO + H2O → Ca(OH)2 (iv) CuSO4 + Zn → ZnSO4 + Cu
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Answer: (i) Combustion (exothermic) (ii) Double displacement (precipitation) (iii) Combination (iv) Displacement
Teacher's Note: Learn this point and write it in your own words.
36. Potassium iodide solution is added to lead(II) nitrate solution. Give the colour of the precipitate, its name, the balanced equation and the type of reaction.
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Answer: Yellow precipitate of lead iodide: 2KI + Pb(NO3)2 → PbI2 + 2KNO3. It is a double displacement (precipitation) reaction.
Teacher's Note: Use the key term in your answer.
37. Potassium chloride solution mixed with silver nitrate gives an insoluble white substance. Write the equation and the types of reaction.
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Answer: KCl(aq) + AgNO3(aq) → AgCl(s) + KNO3(aq). It is a double displacement and a precipitation reaction.
Teacher's Note: Give an example if the question allows.
38. List four observations that show a chemical reaction has taken place.
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Answer: Evolution of a gas, change in temperature, change in state, change in colour (or formation of a precipitate).
Teacher's Note: Write a short, clear answer.
39. Write skeletal equations: (i) hydrogen sulphide reacts with sulphur dioxide to give sulphur and water; (ii) methane burns in oxygen to give carbon dioxide and water. Why do we balance equations?
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Answer: (i) H2S + SO2 → S + H2O; balanced: 2H2S + SO2 → 3S + 2H2O. (ii) CH4 + O2 → CO2 + H2O; balanced: CH4 + 2O2 → CO2 + 2H2O. Equations are balanced to obey the law of conservation of mass, so the number of atoms of each element is the same on both sides.
Teacher's Note: Remember this for your exam.
40. A metal ribbon burns with a dazzling white flame and changes to a white powder. Write the balanced equation.
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Answer: 2Mg + O2 → 2MgO
Teacher's Note: Learn this point and write it in your own words.
41. Name two changes when oily food is oxidised and one way to slow it down.
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Answer: The food turns rancid and its taste and smell change. Keep it in airtight containers or flush with nitrogen.
Teacher's Note: Use the key term in your answer.
42. Identify and define: CH4 + 2O2 → CO2 + 2H2O + heat.
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Answer: An exothermic reaction: one in which heat is released along with the products.
Teacher's Note: Give an example if the question allows.
43. A substance X is used for whitewashing. Name it and write its reaction with water.
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Answer: X is quicklime, CaO. CaO + H2O → Ca(OH)2 (slaked lime).
Teacher's Note: Write a short, clear answer.
44. Why is respiration an exothermic reaction?
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Answer: Food is broken down to release energy: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy.
Teacher's Note: Remember this for your exam.
45. Why are decomposition reactions the opposite of combination reactions? Give equations.
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Answer: A decomposition reaction splits one compound into simpler substances (CaCO3 → CaO + CO2), whereas a combination reaction joins substances into one (CaO + H2O → Ca(OH)2).
Teacher's Note: Learn this point and write it in your own words.
46. In refining silver, silver is recovered from silver nitrate by displacement with copper. Write the reaction.
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Answer: Cu + 2AgNO3 → Cu(NO3)2 + 2Ag
Teacher's Note: Use the key term in your answer.
47. Give reasons: (a) chips bags are flushed with nitrogen; (b) iron articles lose shine; (c) food should be kept in airtight containers.
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Answer: (a) To prevent rancidity. (b) Corrosion of the metal. (c) To prevent oxidation.
Teacher's Note: Give an example if the question allows.
48. What happens when (a) hydrated copper sulphate is heated; (b) gypsum is heated at 373 K; (c) chlorine is passed through dry slaked lime? Give equations.
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Answer: (a) The five molecules of water of crystallisation are lost and blue crystals turn white: CuSO4·5H2O → CuSO4 + 5H2O. (b) Plaster of Paris forms: CaSO4·2H2O → CaSO4·½H2O + 1½H2O. (c) Bleaching powder forms: Ca(OH)2 + Cl2 → CaOCl2 + H2O.
Teacher's Note: Write a short, clear answer.
49. Write the steps for balancing N2 + H2 → NH3.
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Answer: Write the skeletal equation and count the atoms. N is 2 on the left and 1 on the right, so put 2 before NH3; now H is 6 on the right, so put 3 before H2. Balanced: N2 + 3H2 → 2NH3.
Teacher's Note: Remember this for your exam.
50. Give an example of a reaction with (a) change in colour, (b) change in temperature, (c) formation of a precipitate.
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Answer: (a) Pb(NO3)2 + 2KI → PbI2 + 2KNO3 (colourless to yellow). (b) Zn + H2SO4 → ZnSO4 + H2 (heat is evolved). (c) BaCl2 + Na2SO4 → BaSO4 + 2NaCl (white precipitate).
Teacher's Note: Learn this point and write it in your own words.
51. Complete and balance: (i) CaCO3 + HCl (ii) Al + HCl (iii) MnO2 + HCl
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Answer: (i) CaCO3 + 2HCl → CaCl2 + H2O + CO2 (ii) 2Al + 6HCl → 2AlCl3 + 3H2 (iii) MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
Teacher's Note: Use the key term in your answer.
52. Will these reactions take place? (a) Zn + CuSO4 (b) Fe + ZnSO4 (c) Zn + FeSO4
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Answer: (a) Yes; zinc is more reactive than copper. (b) No; iron is less reactive than zinc. (c) Yes; zinc is more reactive than iron.
Teacher's Note: Give an example if the question allows.
53. What is rancidity? Give two ways to prevent it.
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Answer: The bad smell and taste that develops when foods containing fats and oils are oxidised. It is prevented by adding antioxidants and flushing with nitrogen.
Teacher's Note: Write a short, clear answer.
54. Give one example each of decomposition by (i) electricity, (ii) heat, (iii) sunlight, with equations.
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Answer: (i) 2H2O → 2H2 + O2 (ii) CaCO3 → CaO + CO2 (iii) 2AgCl → 2Ag + Cl2
Teacher's Note: Remember this for your exam.
55. Balance: (i) Al + CuCl2 → AlCl3 + Cu (ii) PbO + HCl → PbCl2 + H2O (iii) NH3 + O2 → NO + H2O
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Answer: (i) 2Al + 3CuCl2 → 2AlCl3 + 3Cu (ii) PbO + 2HCl → PbCl2 + H2O (iii) 4NH3 + 5O2 → 4NO + 6H2O
Teacher's Note: Learn this point and write it in your own words.
56. What is a balanced chemical equation? Why must equations be balanced? Balance Al2O3 + NaOH → NaAlO2 + H2O.
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Answer: A balanced equation has the same number of atoms of each element on both sides. It is balanced to obey the law of conservation of mass. Al2O3 + 2NaOH → 2NaAlO2 + H2O.
Teacher's Note: Use the key term in your answer.
57. What is a precipitation reaction? Give an example with a balanced equation.
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Answer: A reaction in which an insoluble substance (precipitate) forms on mixing solutions of two ionic compounds. Example: Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq); BaSO4 is a white precipitate.
Teacher's Note: Give an example if the question allows.
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Useful Resources and Notes for Class 10 Science Chapter 01 Chemical Reactions and Equations
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