# Selina solutions for Concise Science Chemistry 1 Class 9 ICSE chapter 2 - Chemical Changes and Reactions [Latest edition]

## Chapter 2: Chemical Changes and Reactions

Exercise 2 (A)Exercise 2 (B)Exercise 2 (C)
Exercise 2 (A) [Pages 23 - 24]

### Selina solutions for Concise Science Chemistry 1 Class 9 ICSE Chapter 2 Chemical Changes and Reactions Exercise 2 (A) [Pages 23 - 24]

Exercise 2 (A) | Q 1.1 | Page 23

What is a chemical reaction?

Exercise 2 (A) | Q 1.2 | Page 23

State the conditions necessary for a chemical change or reaction.

Exercise 2 (A) | Q 2.1 | Page 23

Define the following terms

Chemical bond

Exercise 2 (A) | Q 2.2 | Page 23

Define the following terms:

Effervescence

Exercise 2 (A) | Q 2.3 | Page 23

Define the following terms

Precipitate

Exercise 2 (A) | Q 3.1 | Page 23

Give an example of a reaction where the following are involved

Heat

Exercise 2 (A) | Q 3.2 | Page 23

Give an example of a reaction where the following are involved

Light

Exercise 2 (A) | Q 3.3 | Page 23

Give an example of a reaction where the following are involved

Electricity

Exercise 2 (A) | Q 3.4 | Page 23

Give an example of a reaction where the following are involved

Close contact

Exercise 2 (A) | Q 3.5 | Page 23

Give an example of a reaction where the following are involved

Solution

Exercise 2 (A) | Q 3.6 | Page 23

Give an example of a reaction where the following are involved

Pressure

Exercise 2 (A) | Q 3.7 | Page 23

Give an example of a reaction where the following are involved

Catalyst

Exercise 2 (A) | Q 4.1 | Page 23

Define Photochemical reaction
Give an example

Exercise 2 (A) | Q 4.2 | Page 23

Define Electrochemical reaction
Give an example

Exercise 2 (A) | Q 5.1 | Page 23

Give an example of each of the following chemical changes:

A photochemical reaction involving

(i) silver salt (ii) water

Exercise 2 (A) | Q 5.2 | Page 23

Give an example of each of the following chemical changes:

A reaction involving

(i) blue solution

(ii) formation of dirty green precipitate

Exercise 2 (A) | Q 5.3 | Page 23

Give an example of the following chemical change.

Two gases combine to form white solid

Exercise 2 (A) | Q 5.4 | Page 23

Give an example of the following chemical change.

Two solids combine to form a liquid

Exercise 2 (A) | Q 5.5 | Page 23

Give an example of the following chemical change.

A reaction where colour change is noticed

Exercise 2 (A) | Q 6.1 | Page 24

Write the chemical reaction where the following changes are observed.

Gas is evolved

Exercise 2 (A) | Q 6.2 | Page 24

Write the chemical reaction where the following changes are observed.

Colour change is noticed

Exercise 2 (A) | Q 6.3 | Page 24

Write the chemical reaction where the following changes are observed.

Precipitate is formed

Exercise 2 (A) | Q 6.4 | Page 24

Write the chemical reaction where the following changes are observed.

Physical state is changed

Exercise 2 (A) | Q 7.1 | Page 24

Give reason for the following:

Silver nitrate solution is kept in coloured bottles.

Exercise 2 (A) | Q 7.2 | Page 24

Give reason for the following:

Molybdenum is used in the manufacture of ammonia.

Exercise 2 (A) | Q 7.3 | Page 24

Give reason for the following:

Blue solution of copper sulphate changes to green when a piece of iron is added to this solution.

Exercise 2 (A) | Q 7.4 | Page 24

Give reason for the following:

Colourless concentrated sulphuric acid in a test tube changes to blue on adding a small piece of copper to it.

Exercise 2 (B) [Page 29]

### Selina solutions for Concise Science Chemistry 1 Class 9 ICSE Chapter 2 Chemical Changes and Reactions Exercise 2 (B) [Page 29]

Exercise 2 (B) | Q 1.1 | Page 29

Complete the following statement.

The chemical change involving iron and hydrochloric acid illustrates a _________________ reaction.

Exercise 2 (B) | Q 1.2 | Page 29

Complete the following statement.

In the type of reaction called_______________, two compounds exchange their positive and negative radicals.

Exercise 2 (B) | Q 1.3 | Page 29

Complete the following statement.

A catalyst either ______ or _____________ the rate of a chemical change but itself remains ______________ at the end of the reaction.

Exercise 2 (B) | Q 1.4 | Page 29

Complete the following statement.

On heating, hydrated copper sulphate changes its colour from ________ to __________.

Exercise 2 (B) | Q 2 | Page 29

When hydrogen burns in oxygen, water is formed; when electricity is passed through water, hydrogen and oxygen are given out. Name the type of chemical change involved in the two cases.

Exercise 2 (B) | Q 3.1 | Page 29

Explain, giving one example for each of the following chemical changes:

Double decomposition

Exercise 2 (B) | Q 3.2 | Page 29

Explain, giving one example of the following chemical change:

Thermal decomposition

Exercise 2 (B) | Q 3.3 | Page 29

Explain,giving one example of the following chemical changes:

Reversible reaction

Exercise 2 (B) | Q 3.4 | Page 29

Explain, giving one example for each of the following chemical changes:

Displacement

Exercise 2 (B) | Q 4 | Page 29

(a) What is synthesis?

(b) What kind of chemical reaction is synthesis? Support your answer by an example.

Exercise 2 (B) | Q 5 | Page 29

Decomposition brought about by heat is known as thermal decomposition. What is the difference between thermal dissociation and thermal decomposition?

Exercise 2 (B) | Q 6 | Page 29

(a) Define the neutralization reaction with an example.

(b) Give a balanced equation for this reaction.

(c) Give three applications of neutralization reactions.

Exercise 2 (B) | Q 7 | Page 29

What do you understand by precipitation reaction? Explain with examples.

Exercise 2 (B) | Q 8.1 | Page 29

What are double displacement reaction?

Exercise 2 (B) | Q 9.1 | Page 29

What is a decomposition reaction?

Exercise 2 (B) | Q 9.2 | Page 29

Decomposition reactions can occur by heat.

Give two balanced reactions for each.

Exercise 2 (B) | Q 9.2 | Page 29

Decomposition reactions can occur by electricity
Give balanced reactions.

Exercise 2 (B) | Q 9.2 | Page 29

Decomposition reactions can occur by sunlight.

Give two balanced reactions.

Exercise 2 (B) | Q 10.01 | Page 29

State the type of reactions for the following represent and balance the ones that are not balanced.

Cl2 + 2KBr → 2KCl + Br2

Exercise 2 (B) | Q 10.02 | Page 29

State the type of reactions for the following represent and balance the ones that are not balanced.

NaOH + HCl → NaCl + H2O

Exercise 2 (B) | Q 10.03 | Page 29

State the type of reactions for the following represent and balance the ones that are not balanced.

2HgO → 2Hg + O2

Exercise 2 (B) | Q 10.04 | Page 29

State the type of reactions for the following represent and balance the ones that are not balanced.

Fe + CuSO4→ FeSO4 + Cu

Exercise 2 (B) | Q 10.05 | Page 29

State the type of reactions for the following represent and balance the ones that are not balanced.

PbO2 + SO2→ PbSO4

Exercise 2 (B) | Q 10.06 | Page 29

State the type of reactions for the following represent and balance the ones that are not balanced.

2KClO3→ 2KCl + 3O2

Exercise 2 (B) | Q 10.07 | Page 29

State the type of reactions for the following represent and balance the ones that are not balanced.

2H2O2→ 2H2O + O2

Exercise 2 (B) | Q 10.08 | Page 29

State the type of reactions for the following represent and balance the ones that are not balanced.

KNO3 + H2SO→ HNO3 + KHSO4

Exercise 2 (B) | Q 10.09 | Page 29

State the type of reactions for the following represent and balance the ones that are not balanced.

CuO+H2→ Cu+ H2

Exercise 2 (B) | Q 10.1 | Page 29

State the type of reactions for the following represent and balance the ones that are not balanced.

CaCO3→ CaO+ CO2

Exercise 2 (B) | Q 10.11 | Page 29

State the type of reactions for the following represent and balance the ones that are not balanced.

NH4Cl → NH3 + HCl

Exercise 2 (B) | Q 10.12 | Page 29

State the type of reactions for the following represent and balance the ones that are not balanced.

PbO + 2HNO3→ Pb(NO3) + 2H2

Exercise 2 (B) | Q 10.13 | Page 29

State the type of reactions for the following represent and balance the ones that are not balanced.

AgNO3 + NaCl → AgCl + NaNO3

Exercise 2 (B) | Q 11 | Page 29

Match the following:

 a. Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g) i. Photochemical decomposition b. $\ce{2AgCI(s) ->[Sunlight] 2Ag(s) + CI2(g)}$ ii. Thermal decomposition c. $\ce{2KCI ->[Electricity] 2K + CI2}$ iii. Displacement reaction d.  $\ce{2HgO(s) ->[\Delta] 2Hg(s) + O(g)}$ iv. Electrolytic decomposition
Exercise 2 (B) | Q 12.1 | Page 29

Multiple choice:

Which of the following is not a characteristic of a chemical change?

•  It is irreversible.

• No net energy change is involved.

• New substance is formed.

•  Involves absorption or liberation of energy.

Exercise 2 (B) | Q 12.2 | Page 29

Multiple choice:

A reaction of a type: AB + CD → AD + CD, involves

•  No chemical change

•  Decomposition of AB and CD

•  Exchange of ions of AB and CD

• Combination of AB and CD

Exercise 2 (B) | Q 12.3 | Page 29

Multiple choice:

The reaction BaCl2(aq) + H2SO4(aq) → BaSO4(s) + 2HCl(aq) is

• Displacement reaction

• Neutralisation reaction

• Decomposition reaction

• Double displacement reaction

Exercise 2 (B) | Q 12.4 | Page 29

Multiple choice:

Thermal decomposition of sodium carbonate will produce

•  Carbon dioxide

•  Oxygen

•  Sodium hydroxide

• No other product

Exercise 2 (C) [Page 32]

### Selina solutions for Concise Science Chemistry 1 Class 9 ICSE Chapter 2 Chemical Changes and Reactions Exercise 2 (C) [Page 32]

Exercise 2 (C) | Q 1 | Page 32

What is a chemical change? Give two examples of chemical change?

Exercise 2 (C) | Q 2 | Page 32

Why energy is involved in a chemical change?

Exercise 2 (C) | Q 3 | Page 32

What do you understand by 'chemical reaction'?

Exercise 2 (C) | Q 4.1 | Page 32

Give an example of a reaction where the following is involved .

Evolution of heat

Exercise 2 (C) | Q 4.2 | Page 32

Give an example of a reaction where the following is involved .

Absorption of heat

Exercise 2 (C) | Q 4.3 | Page 32

Give an example of a reaction where the following is involved .

High pressure is required

Exercise 2 (C) | Q 5 | Page 32

State The main characteristic of chemical reactions. Give at least one example in each case.

Exercise 2 (C) | Q 6.1 | Page 32

Give an example of the following chemical changes.

A reaction involving

(i) Change of state

(ii) formation of precipitate

Exercise 2 (C) | Q 6.2 | Page 32

Give an example of the following chemical changes.

An exothermic and an endothermic reaction involving carbon as one of the reactants.

Exercise 2 (C) | Q 6.3 | Page 32

Give an example of the following chemical changes.

A reaction where colour change is noticed.

Exercise 2 (C) | Q 7 | Page 32

Define exothermic and endothermic changes. Give two example in each case.

Exercise 2 (C) | Q 8 | Page 32

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

Exercise 2 (C) | Q 8.2 | Page 32

Give an example of double displacement reaction, where a gas is evolved.

Exercise 2 (C) | Q 9.1 | Page 32

Define:
Photochemical reaction
Give one example

Exercise 2 (C) | Q 9.2 | Page 32

Define:
Electrochemical reaction
Give one example

Exercise 2 (C) | Q 10.1 | Page 32

Complete and balance the following reaction:

NaCl(aq) + AgNO3(aq) →

Exercise 2 (C) | Q 10.2 | Page 32

Complete and balance the following reaction:

Pb(NO3)2 + KI →

Exercise 2 (C) | Q 10.3 | Page 32

Complete and balance the following reaction:

$\ce{CuCO3 ->[\Delta]}$

Exercise 2 (C) | Q 10.4 | Page 32

Complete and balance the following reaction:

$\ce{Pb(NO3)2 ->[\Delta]}$

Exercise 2 (C) | Q 10.5 | Page 32

Complete and balance the following reaction:

$\ce{NH3 + O2 ->[\Delta]}$

Exercise 2 (C) | Q 11.1 | Page 32

What do you observe? When

Exercise 2 (C) | Q 11.2 | Page 32

What do you observe? When

Silver chloride is exposed to sunlight.

Exercise 2 (C) | Q 11.3 | Page 32

What do you observe? When Hydrogen peroxide is exposed to sunlight.

Exercise 2 (C) | Q 11.4 | Page 32

What do you observe? When H2S gas is passed through copper sulphate solution.

Exercise 2 (C) | Q 11.5 | Page 32

What do you observe? When

Barium chloride is added to sodium sulphate solution

Exercise 2 (C) | Q 11.6 | Page 32

What do you observe? When

Water is added to the quick lime.

Exercise 2 (C) | Q 11.7 | Page 32

What do you observe? When

Sodium chloride solution is added to silver nitrate solution.

Exercise 2 (C) | Q 12.1 | Page 32

Name a carbonate which do not decompose on heating.

Exercise 2 (C) | Q 12.2 | Page 32

Name a nitrate which produces oxygen as the only gas.

Exercise 2 (C) | Q 12.3 | Page 32

Name a compound which produces carbon dioxide on heating.

Exercise 2 (C) | Q 12.4 | Page 32

Name a nitrate which produces brown gas on heating.

## Chapter 2: Chemical Changes and Reactions

Exercise 2 (A)Exercise 2 (B)Exercise 2 (C)

## Selina solutions for Concise Science Chemistry 1 Class 9 ICSE chapter 2 - Chemical Changes and Reactions

Selina solutions for Concise Science Chemistry 1 Class 9 ICSE chapter 2 (Chemical Changes and Reactions) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CISCE Concise Science Chemistry 1 Class 9 ICSE solutions in a manner that help students grasp basic concepts better and faster.

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Concepts covered in Concise Science Chemistry 1 Class 9 ICSE chapter 2 Chemical Changes and Reactions are Classification of Change: Chemical Changes, Conditions Necessary for Chemical Reactions, Types of Chemical Change or Chemical Reaction, Direct Combination (or Synthesis) Reaction, Decomposition Reactions, Single Displacement Reactions, Double Displacement Reaction, Energy Change in Chemical Reactions, Chemical Reaction.

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