NCERT Solutions for Class 10 Science
Chapter 1 Chemical Reactions and Equations
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NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations
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)
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: Reaction between dilute hydrochloric acid and iron filling is given by –
Fe(s) + 2HCl(l) ⟶ FeCl2(aq) + H2
From reaction, hydrogen gas is evolved and iron chloride is formed.
4. What is a balanced chemical equation? Why should chemical equations be balanced?
Answer: Balanced chemical equation is a chemical reaction in which atoms in the reaction are balanced on both the sides. As per the law of conservation of mass, mass can neither be created nor be destroyed. Therefore, mass of atoms in reactant and products should be equal. This, suggest that total number of atoms of each element on both sides of the reaction should be same. However, all reaction should obey the law, therefore, it is necessary to balance the reaction.
5. Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
Answer: H2 + N3 ⟶ NH3
Balanced equation: 3H2 + N2 ⟶ 2NH3
(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
Answer: H2S + O2 ⟶ H2O + SO2
Balanced equation: 2H2S + 3O2 ⟶ 2H2O + 2SO2
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
Answer: BaCl2 + Al2(SO4)3 ⟶ AlCl3 + BaSO4
Balanced equation: 3BaCl2 + Al2(SO4)3 ⟶ 2AlCl3 + 3BaSO4
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Answer: K + H2O ⟶ KOH + H2
Balanced equation : 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) 2 HNO3 + 2 Ca(OH)2 → 2 Ca(NO3)2 + 2 H2O
(b) 6 NaOH + 3 H2SO4 → 3 Na2SO4 + 6 H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + 2 HCl
7. Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
Answer: 2 Ca(OH)2 + 2 CO2 ⟶ 2 CaCO3 + 2 H2O
(b) Zinc + Silver nitrate → Zinc nitrate + Silver
Answer: Zn + 2AgNO3 ⟶ Zn(NO3)2 + 2Ag
(c) Aluminium + Copper chloride → Aluminium chloride + Copper
Answer: 2 Al + 3 CuCl2 ⟶ 2 AlCl3 + 3 Cu
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride
Answer: 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)
Answer: 2KBr(aq) + BaI(aq) ⟶ 2KI(aq) + BaBr2(s)
The given reaction is displacement reaction.
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
Answer: ZnCO3 ⟶ ZnO + CO2
The given reaction is decomposition reaction.
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
Answer: H2 + Cl2 ⟶ 2 HCl
The given reaction is combination reaction.
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)
Answer: Mg + 2HCl ⟶ MgCl2 + H2
The given reaction is displacement reaction.
9. What does one mean by exothermic and endothermic reactions? Give examples.
Answer: When energy is released during the reaction, it is said to be exothermic reaction. Examples of exothermic reaction are explosions, nuclear reactions, etc. When energy is absorbed during the reaction, it is said to be endothermic reaction. Examples of endothermic reaction are evaporation, melting of ice, etc.
10. Why is respiration considered an exothermic reaction? Explain.
Answer: Living organisms acquire energy from food. During the process of digestion, complex substance in the food is broken down into glucose i.e. simpler substance. In the cell, glucose combines with oxygen to generate energy. This occurs during respiration. As energy is released therefore, respiration is known as exothermic reaction.
C6H12O2 + 6O2 ⟶ 6CO2 + 6H2O + Energy
11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer: In decomposition reaction, a compound breaks into two or more substances. These reactions proceeds by acquiring energy. In combination reaction, two or more substances combines to form a compound, thereby releasing the energy. Thus, decomposition reactions are called opposite reactions of the combination reaction. The general form of decomposition and combination reaction is given by-
Decomposition Reaction: AB + Energy ⟶ A + B
Example : 2H2O ⟶ 2H2 + O2
Combination Reaction: A + B ⟶ AB + Energy
Example : 2H2 + O2 ⟶ 2H2O + Energy
12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Answer: Decomposition reaction in presence of heat:
2 FeSO4 ⟶ heat Fe2O3 + SO2 + SO3
Decomposition reaction in presence of light:
2 AgCl ⟶ light 2Ag + Cl2
Decomposition reaction in presence of electricity:
2Al2O3 ⟶ electricity 4Al + 3O2
13. What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Answer:
| Displacement Reaction | Double Displacement Reaction |
|---|---|
| In this reaction more reactive element replaces less reactive element in a compound. | In this reactions, atoms or group of atoms interchange their places to form a new compound. |
| General form: A + BX ⟶ AX + B | General form: AB + CD ⟶ AD + CB |
| Example: CuSO4 + Zn ⟶ ZnSO4 + Cu | Example: Na2SO4 + BaCl2 ⟶ BaSO4 + 2NaCl |
14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
Answer: 2 AgNO3 + Cu ⟶ Cu(NO3)2 + 2 Ag
15. What do you mean by a precipitation reaction? Explain by giving examples.
Answer: Reaction in which precipitate is formed, which is an insoluble substance. Such reaction is called precipitate reaction.
Na2SO4 + BaCl2 ⟶ BaSO4 + 2NaCl
(Precipitate)
16. Explain the following in terms of gain or loss of oxygen with two examples each. (a) Oxidation (b) Reduction
Answer: (a) Oxidation – It is addition of oxygen to respective element
For example: CO2 + H2 ⟶ CO + H2O
In this example, oxygen is added to hydrogen forming water (H2O).
(b) Reduction – It is removal of oxygen from a respective element.
For example: CO2 + H2 ⟶ CO + H2O
In this example, oxygen is removed from carbon dioxide (CO2)
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: Shiny brown coloured element X is copper and black colour substance is copper oxide (CuO). Following is the reaction forming copper oxide from copper –
2Cu + O2 ⟶ 2CuO
(Copper) (Oxygen) (Copper Oxide)
18. Why do we apply paint on iron articles?
Answer: Paint is applied on iron articles as, it acts as a protective layer and prevent iron from rusting. Paint cuts the contact of air and moisture from iron and therefore, rusting of iron is prevented.
19. Oil and fat containing food items are flushed with nitrogen. Why?
Answer: Nitrogen gas does not reacts easily with other substance. Oxygen reacts with food materials containing oils and fats and makes them rancid. Bags used in packing such food materials in flushed with nitrogen in order to remove oxygen from it and since nitrogen does not react with food materials, it prevent food materials from getting rancid.
20. Explain the following terms with one example each. (a) Corrosion (b) Rancidity
Answer: (a) Corrosion – Corrosion is defined as process in which materials loses their strength and quality due to chemical reactions with moisture, air, etc. it is usually seen in metals.
Example : Rusting of iron in presence of moisture and air. Reaction can be given as –
4 Fe + 3 O2 + nH2O ⟶ 2Fe2O3.nH2O
(Hydrated iron oxide or rust)
(b) Rancidity – Rancidity is oxidation of oils and fats, which brings change in odour and taste of food materials.
Example : Change in odour and taste of butter or oil takes place, when used after a long period of time.
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Chapter 1 – Chemical Reactions and Equations?
