Chemical Changes and Reactions Exe-2C Long Answer Chemistry Class-9 ICSE Selina Publishers

Chemical Changes and Reactions Exe-2C Long Answer Chemistry Class-9 ICSE Selina Publishers Solutions Chapter-2. Step By Step ICSE Selina Concise Solutions of Chapter-2 Chemical Changes and Reactions with All Exercise including MCQs, Very Short Answer Type, Short Answer Type, Long Answer Type, Numerical and Structured/Application Questions Solved . Visit official Website CISCE for detail information about ICSE Board Class-9.

Chemical Changes and Reactions Exe-2C Long Answer Chemistry Class-9 ICSE Concise Selina Publishers

Board ICSE
Publications Selina Publication
Subject Chemistry
Class 9th
Chapter-2 Chemical Changes and Reactions
Book Name Concise
Topics Solution of Exercise – (2C) Long/Descriptive Answer Type
Academic Session 2023-2024

D. Exercise – (2C) Long/Descriptive Answer Type

Chemical Changes and Reactions Class-9 Chemistry Concise Solutions  

Page 34

Question 1.

State the main characteristics of chemical reactions. Give at least one example in each case.

Answer:

(i) Evolution of gas

Example:

Zn +           H2SO4               →           ZnSO4          +           H2

[Zinc]  + [dil.sulphuricAcid]        [zinc sulphate]        [hydrogen]

(ii)  Change of colour

Example:

Fe +      CuSO4 (aq)    →             FeSO4   +             Cu

[Iron]   [Blue solution]         [Green Solution]   [copper]

(iii) Formation of precipitates:

Example:

AgNO3 (aq)              +        NaCl(aq)     →              AgCl(ppt)     +    NaNO3(aq)

Question 2.

State the effects of endothermic and exothermic reactions on the surroundings with examples.

Answer:

Exothermic reactions are spontaneous and warm their surroundings with the release of heat energy.

Ex. CH4 + 2O2 ⟶ CO2 ↑ + 2H2O + Heat

Endothermic reactions absorb heat energy from their surroundings and cause their surroundings to cool down.

Ex. C + 2S →Δ​ CS2

Question 3.

Complete and balance the following reactions:

(a) NaCl (aq) + AgNO3 (aq) →

(b) Pb(NO3)2 + KI →

(c) CuCO3

(d) Pb(NO3)2

(e) CO2 + H2O Chlorophyll  → sunlight ​

Answer:

(a) NaCl (aq.) + AgNO3 (aq.) ⟶ AgCl (white ppt.) ↓ + NaNO3 (aq.)

(b) Pb(NO3)2 (s) + 2KI (s) ⟶ 2KNO3 + PbI2 (s)

(c) CuCO3 (s) →Δ​ CuO (s) + CO2 (g)

(d) Pb(NO3)2 →Δ​ 2PbO + 4NO2 + O2

(e)  6CO2 + 6H2O  Chlorophyll  → sunlight C6H12O6 + 6O2

Question 4.

What do you observe? When

(a) Lead nitrate is heated.

(b) Silver chloride is exposed to sunlight.

(c) Hydrogen peroxide is exposed to sunlight.

(d) H2S gas is passed through copper sulphate solution.

(e) Barium chloride is added to sodium sulphate solution

(f) Water is added to the quick lime.

(g) Sodium chloride Answer is added to silver nitrate solution.

Answer:

(a) Lead nitrate decomposes on heating, leaving a yellow residue of lead monoxide, and brown nitrogen dioxide and colourless oxygen gases are evolved.

(b) Due to thermal decomposition, silver chloride breaks down into silver and chloride.

(c) Hydrogen peroxide breaks down to form water and oxygen gas along with heat energy.

(d) When hydrogen sulphide is passed through a blue Answerof copper sulphate, a black precipitate of copper sulphide is obtained, and sulphuric acid so formed remains in the solution.

(e) A white insoluble precipitate of barium sulphate is formed.

(f) Quick lime reacts vigorously with water to produce slaked lime, i.e. calcium hydroxide.

(g) When sodium chloride is added to the silver nitrate solution, a white curdy precipitate of silver chloride is formed.

Question 5.

Discuss the factors that affect a chemical change.

Answer:

Certain chemical reactions occur only when electricity is passed through the reactants.
2NaCl → electricity​ 2Na + Cl2 ↑

Some chemical reactions occur when the involved substances are subjected to high pressure.
N2 + 3H2 ⇌ above 200 atm 2NH3 ↑

Some chemical reactions need a catalyst to accelerate or decelerate the rate at which they occur.
2H2O2 →MnO2​​ 2H2O + O2 ↑

Some chemical reactions take place by the action of light.
2AgCl (s) → sunlight ​ 2Ag (s) + Cl2 (g)

Some chemical reactions take place when two substances are mixed in their solid state.
Pb(NO3)2 (s) + 2KI (s) ⟶ 2KNO3 + PbI2 (s)

Question 6.

Balance these reactions and state what type of reactions they are:

(a) NaNO3 ⟶ NaNO2 + O2

(b) AgNO3 + Zn ⟶ Zn(NO3)2 + Ag

(c) Fe + HCl ⟶ FeCl2 + H2

(d) AgNO3 ⟶ Ag + NO2 + O2

(e) NaBr + Cl2 ⟶ NaCl + Br2

(f) PbO + C ⟶ Pb + CO2

(g) KClO3 ⟶ KCl + O2

(h) AgNO3 + HCl ⟶ AgCl ↓ + HNO3

(i) NH3 + HCl ⟶ NH4Cl

(j) N2 + H2 ⟶ NH3

Answer:

(a) 2NaNO3 ⟶ 2NaNO2 + O2 ↑

Decomposition reaction

(b) 2AgNO3 + Zn ⟶ Zn(NO3)2 + 2Ag

Displacement reaction

(c) Fe + 2HCl ⟶ FeCl2 + H2 ↑

Displacement reaction

(d) 2AgNO3 ⟶ 2Ag + 2NO2 ↑ + O2 ↑

Decomposition reaction

(e) 2NaBr + Cl2 ⟶ 2NaCl + Br2

Displacement reaction

(f) 2PbO + C ⟶ 2Pb + CO2 ↑

Displacement reaction

(g) 2KClO3 ⟶ 2KCl + 3O2 ↑

Decomposition reaction

(h) AgNO3 + HCl ⟶ AgCl ↓ + HNO3

Double decomposition reaction

(i) NH3 + HCl ⟶ NH4Cl

Direct combination reaction

(j) N2 + 3H2 ⟶ 2NH3 ↑

Direct combination reaction

Question 7.

Explain the different types of double decomposition reactions by giving suitable equations.

Answer:

Different types of double decomposition reactions are:

1. Precipitation reaction — A reaction between two compounds in aqueous solution state to give two new compounds one of which is insoluble (precipitate) is called a Precipitation reaction.
For example, when H2S is passed through copper sulphate solution, a black precipitate of copper sulphide is obtained.
CuSO4 (aq) + H2S (g) ⟶ CuS [black ppt.] ↓ + H2SO4

2. Neutralization reaction — The reaction between an acid and a base that forms salt and water only is referred to as Neutralization reaction.
For example, Sodium chloride (base) reacts with HCl (acid) to form salt and water only.
NaOH + HCl ⟶ NaCl + H2O

Question 8.

Explain thermal dissociation and thermal decomposition reactions with examples. What is the difference between them ?

Answer:

A reversible decomposition reaction brought about only by heat is called thermal dissociation reaction.

For example, on application of heat, ammonium chloride decomposes into Ammonia and HCl:

NH4Cl ⇌ NH3 + HCl

A chemical reaction in which a compound decomposes to give two new elements / a new compound & an element / two new compounds on application of heat without any recombination on cooling is called a Thermal decomposition reaction.

For example, calcium carbonate decomposes to carbon dioxide and calcium oxide when heated to 1000°C

CaCO3 (s) → Δ​ CaO (s) + CO2 (g)

Difference between the two is that thermal dissociation is a reversible decomposition reaction whereas, thermal decomposition is an irreversible reaction.

Question 9.

Metal X was placed in lead nitrate solution. A thin layer of lead metal deposits on metal X. Which is more reactive metal X or lead ? State the type of reaction and give an example of this type.

Answer:

Metal X is more active metal because it displaced the metal lead from lead nitrate. It is a displacement reaction.

CuSO4 + Zn ⟶ ZnSO4 + Cu

Zn is more active metal than Cu, and it displaces Cu from copper sulphate.

Question 10.

What type of reaction is respiration ? Explain.

Answer:

Respiration is an exothermic reaction as it involves combustion of glucose with oxygen in the cells of the body releasing heat energy that is used by cells to perform various functions such as muscle contraction, nerve impulse transmission, and protein synthesis. The equation for respiration reaction is:

C6H12O6 + 6O2 ⟶ + 6CO2 ↑ + 6H2O + Heat energy

Question 11.

Discuss some decomposition reactions occurring inside our body.

Answer:

Digestion of food in our body is an example of decomposition reaction.

The starch present in the food we eat decomposes into glucose and sugar. Proteins undergo decomposition to form amino acids. Fats and oils are decomposed to fatty acids and finally oxidized by respiration into carbon dioxide and water.

Starch →Enzymes Glucose →[O] CO2 + H2O + Energy

—  : End of Chemical Changes and Reactions Exe-2C Long/Descriptive Answer Class-9 ICSE Chemistry Solutions :–

Return to  Return to Concise Selina ICSE Chemistry Class-9 

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