Class 10 Ncert Chapter 1

Chemistry

(7) Write the balanced chemical equation for the following reactions.

Calcium hydroxide + Carbon dioxide —-> Calcium carbonate + Water

Zinc + Silver nitrate —-> Zinc nitrate + Silver

Aluminium + Copper chloride —-> Aluminium chloride + Copper

Barium chloride + Potassium sulphate —-> Barium sulphate + Potassium chloride

Solution:

2Ca(OH)₂ + 2CO₂ → 2CaCO₃ + 2H₂O

Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag

2Al + 3CuCl₂ → 2AlCl₃ + 3Cu

BaCl₂ + K₂SO₄ → BaSO₄ + 2KCl

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

KBr + BaI₂ → KI + BaBr₂

ZnCO₃ → ZnO + CO₂

H₂ + Cl → HCl

Mg + HCl → MgCl₂ + H₂

Solution

2KBr + BaI₂ → 2KI + BaBr₂ (Double Displacement Reaction)

ZnCO₃ → ZnO + CO₂ (Decomposition Reaction)

H₂ + Cl → 2HCl (Combination Reaction

Mg + 2HCl → MgCl₂ + H₂ (Displacement Reaction)

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9. What is meant by exothermic and endothermic reactions? Give examples

An endothermic reaction occurs when energy is absorbed from the surroundings in the form of heat.(Example: Photosynthesis, melting of ice, evaporation). Conversely, an exothermic reaction is one in which energy is released from the system into the surroundings. (Example: Explosions, concrete setting, nuclear fission and fusion).

10. Why is respiration considered to be an exothermic reaction?

For the survival of life, we require energy. We obtain this energy from the food we eat. The food molecules, through the process of digestion, is broken down into a simpler molecule like glucose. These substances come in contact with the Oxygen present in our body cells to form Carbon dioxide and water along with a certain amount of energy (Respiration process). Since the energy is in the form of heat (that maintains our body temperature) the respiration is considered to be an exothermic reaction. The reaction taking place is:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy

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

Combination reaction is said to be the reaction between two or more molecules to form a larger molecule; whereas the decomposition reaction is defined as the splitting of larger molecules into two or more smaller molecules. This essentially explains that the decomposition reaction is the opposite of the combination reaction.

In most of the cases the decomposition reaction is endothermic since heat from the surrounding or induced heat is used to break the bonds of the larger molecule. Few examples of decomposition reactions are:

ZnCO₃ → ZnO + CO₂

CaCO₃ + Energy → CaO + CO₂

2HgO → 2Hg + O₂

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

Solution

Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)

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

When two solutions containing soluble salts are combined, a double displacement reaction takes place in which the ions are exchanged between the compounds. When one of such compounds formed is in solid form (that is insoluble in aqua) then it settles down at the bottom of the container. This solid is known as the precipitate and the respective reaction is termed as the precipitation reaction. Few examples of precipitation reactions are:

CdSO₄(aq) + K₂S(aq) → CdS(s) + K₂SO₄(aq)

2NaOH(aq) + MgCl₂(aq) → 2NaCl(aq) + Mg(OH)₂(s)