CBSE – 10th Standard Science

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Class 10 Question Bank Chapter 1 – Chemicals Reactions and Equations

Qus 1. What happens when  a magnesium ribbon is burnt in oxygen ?

Ans. When a magnesium ribbon is burnt in oxygen, it gets converted to magnesium oxide.

Qus 2. Does number of atoms of each element remains the same, before and after a chemical reaction ?

Ans. No, number of atoms of each element remains the same, before and after a chemical reaction.

Qus 3. What must be remembered when equalizing  the number of atoms ?

Ans. It must be remembered that we cannot alter the formulae of the compounds or elements involved in the reactions.

Qus 4. Write the place of a reactant in an equation ?

Ans. The reactants are written on the left-hand side (LHS) of an equation.

Qus 5. What must be done to check the correctness of the balanced equation ?

Ans. To check the correctness of the balanced equation, we count atoms of each element on both sides of the equation.

Qus 6. What is hit – and – trial method ?

Ans. This method of balancing chemical equations is called hit-and-trial method.

Qus 7. What should we do to make a chemical equation more informative ?

Ans. To make a chemical equation more informative, the physical states of the reactants and products are mentioned along with their chemical formulae.

Qus 8. Write the notations of gaseous, liquid, aqueous and solid states ?

Ans. The notations of gaseous, liquid, aqueous and solid states are (g), (l), (aq) and (s).

Qus 9. What happens when calcium oxide is combined with water ?

Ans. Calcium oxide reacts vigorously with water to produce slaked lime when combined with water.

Qus 10. Explain the term combination reaction ?

Ans. A reaction in which a single product is formed from two or more reactants is known as a combination reaction.

Qus 11. What is exothermic chemical reactions ?

Ans. Reactions in which heat is released along with the formation of products are called exothermic chemical reactions.

Qus 12. What is decomposition reaction ?

Ans. Reaction in which a single reactant breaks down to give simpler products is called decomposition reaction.

Qus 13. Write the other name of calcium oxide ?

Ans. Calcium oxide is called lime or quick lime.

Qus 14. Explain the term thermal decomposition ?

Ans. When a decomposition reaction is carried out by heating, it is called thermal decomposition.

Qus 15. What is endothermic reactions ?

Ans. Reactions in which energy is absorbed are known as endothermic reactions.

Qus 16. What is precipitation reaction ?

Ans. Any reaction that produces a precipitate can be called a precipitation reaction.

Qus 17. Explain the term double displacement reactions ?

Ans. The  reactions in which there is an exchange of ions between the reactants are called double displacement reactions.

Qus 18. What is oxidation-reduction reactions

Ans. When one reactant gets oxidised while the other gets reduced during a reaction. Such reactions are called oxidation-reduction reactions.

Qus 19. Explain the process of rusting of iron ?

Ans. When iron articles are shiny when new, but get coated with a reddish brown powder when left for some time. This process is commonly known as rusting of iron.

Que.20 Write the balanced equation for the following chemical reactions.

(i) Hydrogen + Chlorine → Hydrogen chloride

(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride

(iii) Sodium + Water → Sodium hydroxide + Hydrogen

Ans.      (i) H2+Cl2—–à2HCl

(ii) BaCl2+Al2(SO4)3—-àBaSO4+AlCl3

(iii) Na+H2O——àNaOH+H2

Que.21 Write a balanced chemical equation with state symbols for the following reactions.

(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.

(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water

Ans    i)BaCl2(aq)+NaSO4(aq)—àBaSO4(s) +NaCl(aq)

ii)NaOH(aq)+dil.HCl—àNaCl(l)+H2O

Que 22. What does one mean by exothermic and endothermic reactions? Give examples.

Ans. Reactions in which heat is released along with the formation of products are called exothermic chemical reactions.

examples of exothermic reactions are –

(i) Burning of natural gas

CH4(g) + 2O2 (g) → CO2 (g) + 2H2O (g)

(ii) respiration is an exothermic process

(iii) decomposition of vegetable matter into compost is also an example of an exothermic reaction.

Reactions in which energy is absorbed or heat is involved for the reaction are known as endothermic reactions.

For example:-

  • Photosynthesis
  • Dissolving ammonium salts in water

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