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

Chemical Changes and Reactions Exe-2C Short 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 Short 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) Short Answer Type
Academic Session 2023-2024

C. Exercise – (2C) Short Answer Type

Chemical Changes and Reactions Class-9 Chemistry Concise Solutions  

Page 33

Question 1.

Define:

(a) Photochemical reaction

(b) Electrochemical reaction

Give one example in each case.

Answer:

(a) It is a reaction which occurs with absorption of light energy.

Example: Photosynthesis

(b) It is a reaction which occurs with absorption of electrical energy.

Example: Acidulated water breaks into hydrogen and oxygen.


C. Exercise – (2C) Short Answer Type

Chemical Changes and Reactions Class-9 Chemistry Concise Solutions  

Page 34

Question 2.

Give an example of a reaction where the following are involved

(a) Evolution of heat

(b) Absorption of heat

(c) High pressure is required

Answer:

(a) C + O2 → CO2 + Heat

(b) C + 2S  → CS2

(c)  N+ 3H2→ 2NH3

Question 3.

Why does the blue colour of copper sulphate solution fade on adding iron fillings ?

Answer:

Blue colour of copper sulphate fades away as iron displaces copper from copper sulphate solution as iron is more reactive than copper.

Question 4.

Give an example of:

(a) Single displacement reaction

(b) Double displacement reaction

(c) Photochemical reaction

(d) Thermal decomposition reaction

(e) Electrolytic decomposition reaction

(f) Combination reaction between two compounds ?

Answer:

(a) Single displacement reaction

CuSO4 + Zn ⟶ Cu + ZnSO4

(b) Double displacement reaction

BaCl2 (aq) + H2SO4 (aq) ⟶ BaSO4 (s) + 2HCl (aq)

(c) Photochemical reaction

2AgNO3 →sunlight 2Ag + 2NO2 ↑ + O2 ↑

(d) Thermal decomposition reaction

2HgO (s) →Δ 2Hg (l) + O2 (g)

(e) Electrolytic decomposition reaction

2H2O current → electric 2H2 + O2 ↑

(f) Combination reaction between two compounds ?

NH3 + HCl ⟶ NH4Cl

Question 5. 

What do you understand by ‘chemical reaction’?

Answer:

A chemical reaction is the process of breaking the chemical bonds of the reacting substances (reactants) and making new bonds to form new substances (products).

A chemical change or chemical reaction occurs when particles collide. Collisions occur when reactants are in close contact or by supply of energy.

Question 6. 

Give an example of each of the following chemical changes.

(a) A reaction involving

(i) Change of state

(ii) Formation of precipitate

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

(c) A reaction where colour change is noticed.

Answer:

(a) (i) Change of state

Ammonia gas reacts with HCl gas to give solid ammonium chloride.

NH3 (g) + HCl(g) ⇋ NH4Cl(s)

(ii) Formation of precipitate

When a Answe rof silver nitrate is added to a Answer of sodium chloride, a white insoluble substance, silver chloride, is formed.

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

(b) Exothermic reaction:

When carbon burns in oxygen to form carbon dioxide, a lot of heat is produced.

C + O2 → CO2 + Heat

Endothermic reaction:

When carbon is heated with sulphur at high temperature, liquid carbon disulphide is formed.

C + 2S  CS2

(c) Colour change

A few pieces of iron are added into a blue coloured copper sulphate solution; the blue colour of copper sulphate fades and eventually turns into light green due to the formation of ferrous sulphate.

Fe + CuSO4 → FeSO4 + Cu

Question 7.

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

Answer:

A chemical change is a permanent change in which the chemical composition of a substance is changed and a new substance is formed.

Examples:

Heating of copper carbonate

Formation of curd from milk

Question 8.

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

Answer :

Exothermic reaction:

A chemical reaction in which heat is given out is called an exothermic reaction.

Example:

When carbon burns in oxygen to form carbon dioxide, a lot of heat is produced.

C + O2 → CO2 + Heat

When hydrogen is burnt in oxygen, water is formed and heat is released.

2H2 + O 2H2O + Heat

Endothermic reaction:

A reaction in which heat is absorbed is called endothermic reaction.

Example:

When carbon is heated with sulphur at high temperature, liquid carbon disulphide is formed.

C + 2S   CS2

When nitrogen and oxygen are heated together to a temperature of about 3000°C, nitric oxide gas is formed.

N2 O2 + 2NO  

Question 9.

Why energy is involved in a chemical change?

Answer:

In every chemical change, change in energy is involved.

There is a difference between the chemical energies of the reactants and products. It involves the breaking up of chemical bonds between the atoms resulting in the absorption of energy in the form of heat and simultaneous formation of bonds with the release of energy.

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

Return to  Return to Concise Selina ICSE Chemistry Class-9 

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