Class 10 Science Chapter 1 Chemical Reactions and Equations
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Class 10 Science Chapter 1 Chemical Reactions and Equations

Here are Class 10 Science Chapter 1 Chemical Reactions and Equations Question-Answer

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

2PbO(s) + C(s) → 2Pb(s) + CO2(g)

  1. Lead is getting reduced.
  2. Carbon dioxide is getting oxidised.
  3. Carbon is getting oxidised.
  4. Lead oxide is getting reduced.

(i) (a) and (b)

(ii) (a) and (c)

(iii) (a), (b), and (c)

(iv) all

2. Fe2O3 + 2Al → Al2O3 + 2Fe

The above reaction is an example of a

  1. combination reaction.
  2. double displacement reaction.
  3. decomposition reaction.
  4. displacement reaction.

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

  1. Hydrogen gas and iron chloride are produced.
  2. Chlorine gas and iron hydroxide are produced.
  3. No reaction takes place.
  4. Iron salt and water are produced.

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

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

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

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6. Balance the following chemical equations.

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

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

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

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

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

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

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

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

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

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

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

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

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16. Explain the following in terms of gain or loss of oxygen with two examples each.

  1. (a) Oxidation
  2. (b) Reduction

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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.

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18. Why do we apply paint on iron articles?

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

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20. Explain the following terms with one example each.

  1. (a) Corrosion
  2. (b) Rancidity

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Very Important Chemical Reaction Concepts

  • A complete chemical equation represents the reactants, products, and their physical states symbolically.
  • A chemical equation is balanced so that the numbers of atoms of each type involved in a chemical reaction are the same on the reactant and product sides of the equation. Equations must always be balanced.
  • In a combination reaction, two or more substances combine to form a new single substance.
  • Decomposition reactions are opposite to combination reactions. In a decomposition reaction, a single substance decomposes to give two or more substances.
  • Reactions in which heat is given out along with the products are called exothermic reactions.
  • Reactions in which energy is absorbed are known as endothermic reactions.
  • When an element displaces another element from its compound, a displacement reaction occurs.
  • Two different atoms or groups of atoms (ions) are exchanged in double displacement reactions.
  • Precipitation reactions produce insoluble salts.
  • Reactions also involve the gain or loss of oxygen or hydrogen by substances. Oxidation is the gain of oxygen or loss of hydrogen. Reduction is the loss of oxygen or gain of hydrogen.

Chemistry Questions

  1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
  2. Give an example of a double displacement reaction other than the one given in Activity 1.10.
  3. Identify the substances that are oxidised and the substances that are reduced in the following reactions:
    1. 4Na(s) + O2(g) → 2Na2O(s)
    2. CuO(s) + H2(g) → Cu(s) + H2O(l)