Chemical Reactions and Equations - Full Questions and Answers Questions NCERT solution Chapter 1

Class 10 Chemical Reactions and Equations - Full Questions and Answers

1. Which of the statements about the reaction below are incorrect?

2PbO(s) + C(s) → 2Pb(s) + CO₂(g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all

Answer: (i) (a) and (b) are incorrect.

2. Fe₂O₃ + 2Al → Al₂O₃ + 2Fe

The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.

Answer: (d) displacement reaction.

3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.

(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.

Answer: (a) Hydrogen gas and iron chloride are produced.

4. What is a balanced chemical equation? Why should chemical equations be balanced?

Answer: A balanced chemical equation has the same number of atoms of each element on both sides. Equations should be balanced to follow the law of conservation of mass.

5. Translate the following statements into chemical equations and then balance them.

(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Answer:
(a) N₂ + 3H₂ → 2NH₃
(b) 2H₂S + 3O₂ → 2H₂O + 2SO₂
(c) 3BaCl₂ + Al₂(SO₄)₃ → 2AlCl₃ + 3BaSO₄
(d) 2K + 2H₂O → 2KOH + H₂

6. Balance the following chemical equations.

(a) HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O
(b) NaOH + H₂SO₄ → Na₂SO₄ + H₂O
(c) NaCl + AgNO₃ → AgCl + NaNO₃
(d) BaCl₂ + H₂SO₄ → BaSO₄ + HCl

Answer:
(a) 2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O
(b) 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O
(c) Already balanced.
(d) Already balanced.

7. Write the balanced chemical equations for the following reactions.

(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
(c) Aluminium + Copper chloride → Aluminium chloride + Copper
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

Answer:
(a) Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
(b) Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag
(c) 2Al + 3CuCl₂ → 2AlCl₃ + 3Cu
(d) BaCl₂ + K₂SO₄ → BaSO₄ + 2KCl

8. Write the balanced chemical equation for the following and identify the type of reaction in each case.

(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)

Answer:
(a) 2KBr(aq) + BaI₂(aq) → 2KI(aq) + BaBr₂(s) - Double displacement
(b) ZnCO₃(s) → ZnO(s) + CO₂(g) - Decomposition
(c) H₂(g) + Cl₂(g) → 2HCl(g) - Combination
(d) Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g) - Displacement

9. What does one mean by exothermic and endothermic reactions? Give examples.

Answer: Exothermic reactions release heat energy (example: burning coal). Endothermic reactions absorb heat energy (example: photosynthesis).

10. Why is respiration considered an exothermic reaction? Explain.

Answer: Because during respiration, glucose reacts with oxygen and releases energy (heat) in our body, so it is exothermic.

11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

Answer: Combination reactions combine substances to form one compound, while decomposition reactions break one compound into simpler substances. Example: 2H₂ + O₂ → 2H₂O (Combination), 2H₂O → 2H₂ + O₂ (Decomposition).

12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

Answer:
Heat: CaCO₃ → CaO + CO₂
Light: 2AgCl → 2Ag + Cl₂
Electricity: 2H₂O → 2H₂ + O₂

13. What is the difference between displacement and double displacement reactions? Write equations for these reactions.

Answer: Displacement: a more reactive element replaces a less reactive element (Zn + CuSO₄ → ZnSO₄ + Cu). Double displacement: exchange of ions (AgNO₃ + NaCl → AgCl + NaNO₃).

14. In the refining of silver, the recovery of silver from silver nitrate solution involves displacement by copper metal. Write down the reaction involved.

Answer: Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag

15. What do you mean by a precipitation reaction? Explain by giving examples.

Answer: A precipitation reaction forms an insoluble solid from solutions. Example: BaCl₂ + H₂SO₄ → BaSO₄ (solid) + 2HCl

16. Explain the following in terms of gain or loss of oxygen with two examples each: (a) Oxidation (b) Reduction

Answer: Oxidation is the gain of oxygen (examples: 2Mg + O₂ → 2MgO, C + O₂ → CO₂). Reduction is the loss of oxygen (examples: CuO + H₂ → Cu + H₂O, ZnO + C → Zn + CO).

17. A shiny brown coloured element 'X' on heating in air becomes black in colour. Name the element 'X' and the black coloured compound formed.

Answer: 'X' is copper (Cu), and the black compound formed is copper oxide (CuO).

18. Why do we apply paint on iron articles?

Answer: We apply paint on iron articles to prevent rusting. Rusting happens when iron reacts with moisture and oxygen in the air, forming a brown flaky substance called rust. The paint forms a protective layer on the surface of the iron, which stops air and moisture from reaching the iron, thus preventing rust.

19. Oil and fat containing food items are flushed with nitrogen. Why?

Answer: Oil and fat containing food items are flushed with nitrogen to prevent rancidity. Rancidity happens when fats and oils react with oxygen in the air, causing the food to develop a bad smell and taste. Nitrogen is an unreactive gas that does not support oxidation, so flushing food packets with nitrogen pushes out the oxygen and keeps the food fresh for a longer time without spoilage.

20. Explain the following terms with one example each: (a) Corrosion (b) Rancidity

Answer: (a) Corrosion is the slow eating up of metals by air and moisture (example: rusting of iron). (b) Rancidity is the spoilage of oily and fatty foods due to oxidation, producing a bad smell (example: chips left in air become smelly).