NCERT Solutions for class 10 Science Chapter 1 Chemical Reactions And Equations

NCERT Solutions for class 10 Science Chapter 1 Exercise Question

Question 1

Which of the statements about the reaction below are incorrect ?
2 PbO(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)

Question 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.

Question 3

What happens when dilute hydrochloric acid is added to iron filings ? 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.

Question 4

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

Answer

A balanced chemical equation is the total mass of the elements present in products side and in reactant side are equal in chemical reaction

We need to balance chemical equation because it followthe law of conservation of mass.According to this law, mass can neither be created nor be destroyed in a chemical reaction

Question 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) 3H₂ (g) + N₂ (g) → 2NH₃ (g)
(b) H₂S (g) + 3O₂ (g) → SO₂ (g) + 2H₂O(l)
(c) 3BaCl₂ (aq) + Al₂(SO₄)₃ (aq) → 2AlCl₃ (aq) + 3BaSO₄ ↓(s)
(d) 2K (s) + 2H₂O (l) → 2KOH (aq) + H₂ (g)

Question 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) NaCl + AgNO₃ → AgCl + NaNO₃
(d) BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl

Question 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 + 2 Ag
(c) 2Al + 3 CuCl₂ → 2AlCl₃ + 3 Cu
(d) BaCl₂ + K₂SO₄ → BaSO₄ + 2KCl

Question 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
(b) Zinc carbonate(s) → Zinc oxide (s) + Carbon dioxide (g) bromide(s)
(c) Hydrogen (g) + Chloride (g) → Hydrogen chloride (g)
(d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g)

Answer

(a) 2KBr (aq) + Bal₂(aq) → 2Kl(aq) + BaBr₂(s)
Type : Double displacement reaction

(b) ZnCO₃ (s) → ZnO (s) + CO₂ (g)
Type : Decomposition reaction

(c) H₂ (g) + Cl₂ (g) → 2HCl(g)
Type : Combination reaction

(d) Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)
Type : Displacement reaction

Question 9

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

Answer

A reactions in which heat is evolved are known as exothermic reactions
Example :
(i) C (s) + O₂ (g) → CO₂ (g) + Heat
(ii) N₂ (g) + 3H₂ (g) → 2NH₃ (g) + Heat

Endothermic reactions : Those reactions in which heat is absorbed are known as endothermic reactions. it is usually indicated by writing “Heat” on the left side of a chemical equation.
Examples :
(i) C (s) + 2S (s) → CS₂ (l) – Heat
(ii) N₂ (g) + O₂ (g) → 2NO(g) – Heat

Question 10

Why is respiration considered an exothermic reaction ? Explain.

Answer

Respiration is an exothermic process because during respiration glucose combines with oxygen in the cells of our body to form carbon dioxide and water along with the production of energy.

Question 11

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

Answer

In combination reaction when two or more substance combine to form a single product with large amount of heat is called combination reaction For example:
N² + 3H₂ – 2NH₃ + heat;

In a decomposition reaction require energy either in the form of heat or light or electricity for breaking down the reactants into two or more products
2NH₃ + Heat – N₂ + 3H₂;

Question 12

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

Answer

Decomposition reactions involving of heat
CaCo₃(s) – CaO(s) + CO₂(g)
Decomposition reactions involving of light
2AgCl – 2Ag(s) + Cl₂(g)
Decomposition reactions involving of electrical energy
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Question 13

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

Answer

A displacement reactions in which a more reactive metal displaces a less reactive metal from its compound. For example,
Zn(s) + CuSO₄(aq) → Cu(s) + ZnSO₄(aq)
here Zinc is more reactive displaces copper from its solution.
A double displacement reactions, a mutual exchange of ions between two compound to form two new compound. For example,
AgNO₃(aq) + NaCl (aq) → AgCl(s) + NaNO₃ (aq)
Here silver nitrate and sodium chloride exchange Cl^– and NO₃^– and form two new compound.

Question 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

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

Question 15

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

Answer

When two reactants in solution react and one or more of the products form, which is insoluble in water or forms a precipitate, the reaction is called a precipitation reaction
Example : Na₂SO₄

Question 16

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

Answer

(a) Oxidation : It is define as the gain of oxygen to a substance is called oxidation.
(i) C(s) + O₂(g) → CO₂
In the recation C gain oxygen to form CO. (ii) 2Mg(s) + O₂ (g) → 2MgO(s)

In the recation Mg gain oxygen to form MgO.

(b) Reduction : It is define as the loss of oxygen from a substance is called reduction.
Example: (i) CuO + H2 – Cu + H₂O
In the recation copper oxide is being lossing oxygen and it is reduced to copper.

(ii) ZnO + C – Zn + CO
Here, zinc oxide is being lossing oxygen and it is reduced to zinc .

Question 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

Element ‘X’ is copper (Cu).The black coloured compound is copper oxide (CuO).

Question 18

Why do we apply paint on iron articles ?

Answer

We apply paint on iron articles because it does not allow air, moisture to attack on iron articles and there no risk of rusting .

Question 19

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

Answer

Oil and fat containing food items flushed with nitrogen because food get exposed in the presence air and get oxidised which have bed taste and becomes rancid and nitrogen acts as an antioxidant and it prevent them from being oxidised.

Question 20

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

Answer

i. Corrosion: It is a process of slow decay of the metals due to the attack of air, moisture, acids, etc. on the surface of metals is called corrosion. eg. Iron forms reddish brown coloured coating on iron .

ii. Rancidity: The oxidation of oils and fats in foods give a bad smell , taste and unfit for consumption a is called rancidity Rancid of old cooking oil