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Concise Chemistry Class 9 ICSE Solutions for Chapter 2 - Chemical Changes and Reactions

ICSE

Concise Chemistry Class 9 ICSE Solutions for Chapter 2 - Chemical Changes and Reactions

ICSE Class 9 Chemistry Chapter 2 Selina Concise Solutions - Free PDF Download

Updated ICSE Class 9 Chemistry Chapter 2 - Chemical Changes and Reactions Selina Solutions are provided by Vedantu in a step-by-step method. Selina is the most famous publisher of ICSE textbooks. Studying these solutions by Selina Concise Chemistry Class 9 Solutions which are explained and solved by our subject matter experts will help you in preparing for ICSE exams. Concise Chemistry Class 9 ICSE Solutions can be easily downloaded in the given PDF format. These solutions for Class 9 ICSE will help you to score good marks in ICSE Exams 2024-25.

The updated solutions for Selina textbooks are created following the latest syllabus. These are provided by Vedantu in a chapter-wise manner to help the students get a thorough knowledge of all the fundamentals.

Chemical Changes and Reactions

There are constant physical and chemical reactions going on everywhere around us. Let us know the difference between physical and chemical reactions.

Physical Reaction

When there are changes in the physical property of the matter that do not produce any new matter and these changes are visible to us and some of them could be reserved and are not visible to us. Example- When water gets converted into ice in a fridge then its shape is visible to us and this is a physical change.

Chemical Reaction

The changes that happen chemically are known as Chemical change and that leads to the chemical reaction on the body of the matter. Example- The burning of coal produces coal and that happens because of the chemical reaction that takes place.

Characteristics of Physical and Chemical Changes

Physical Changes	Chemical Changes
These involve changes in form or shape but there won't be any impact on the composition	This would have an impact on the chemical composition.
These are reversible.	These are irreversible.
A physical change leads to a change in the physical properties of matter.	A chemical change leads to a change in the chemical properties of matter.

Examples of Physical Changes:

a. It dissolves salt and sugar in water.

b. There would be a sublimation of iodine.

Examples of Chemical Changes:

a. Burning of paper

b. When you cook food.

Conditions for Chemical Change to occur

Chemical changes take place because of the following conditions.

When a substance comes under close contact with another. Example- Coming of sodium in close contact with water then it forms sodium hydroxide and water.
The chemical reaction also takes place because of heat. Example-When iron and sulphur are heated together then there is a formation of FeS.
Chemical reactions also occur because of electricity. Example- When current passes from the water it separates both hydrogen and oxygen and that lead to the process of electrolysis.
Pressure also leads to the chemical reaction and changes its chemical properties. Example- When KClO3 and sulphur together get hit with a hammer then because of pressure chemical reaction takes place and the mixture explodes.
The addition of a catalyst also leads to the chemical reaction Example-KClO3 has to be heated strongly to produce oxygen.

Characteristics of Chemical Reactions

Characteristics	Example
Change in State	CO(g) + 2H2(g) CH3OH(g)
Evolution of gas	Zn + 2 HCl → ZnCl₂ + H₂
Change in Colour	FeSO₄ = Fe₂O₃ + SO₃ + SO₂
Change in Temperature Exothermic reactions(Energy released as heat, light, or sound) Endothermic reactions(Energy absorbed by reactants, temperature drops)	CaO + H₂O → Ca(OH)₂ respiration, combustion Na₂SO₄ + BaCl₂ → NaCl + BaSO₄ photosynthesis

FAQs on Concise Chemistry Class 9 ICSE Solutions for Chapter 2 - Chemical Changes and Reactions

1. What is a chemical reaction? What conditions are required for a chemical reaction to take place?

It is a process of breaking the chemical bond of the reactants to form new bonds and substances.

The conditions which are required for a chemical reaction to take place are as follows:

a. When a substance comes under close contact with another.

b. The chemical reaction also takes place because of heat.

c. Pressure helps in a chemical reaction as well.

d. Electricity is required too.

e .The addition of a catalyst.

2. What are the main characteristics of the chemical reactions?

The main characteristics of chemical reactions are as follows:

a. The evolution of gas.

b. Colour change is also one of the characteristics of a chemical reaction.

c. There would be a formation of precipitation. Few chemical reactions produce some insoluble substances known as precipitates.

d. Change of the state is observed during the chemical reaction. Solid might get converted into liquid and then liquid gets converted into gas when the chemical reaction takes place.

3. What is the difference between double decomposition, thermal decomposition, and reversible reaction?

Double decomposition is a kind of chemical change in which two compounds in a solution get reacted to form two new compounds with the help of a mutual exchange of radicals.

On the other hand, thermal decomposition means decomposition happens because of heat. Thermal decomposition reactions are those reactions that break or get decomposed because of the process based on heating to form many products.

When the direction of the chemical change gets reversed because of the change of the conditions under which the reaction is happening is known as a reversible reaction.

4. What is the difference between physical and chemical reactions?

There is a huge difference between them and they are as follows:

a. When there are changes in the physical property of the matter that do not produce any new matter and these changes are visible to us and some of them could be reserved and are not visible to us. This is known as a Physical reaction Example- When water gets converted into ice in a fridge then its shape is visible to us and this is a physical change.

b. The changes that happen chemically are known as Chemical change and that leads to the chemical reaction on the body of the matter. Example- The burning of coal produces coal and that happens because of the chemical reaction that takes place.

5. Is energy involved in a chemical change?

There is a presence of energy when a chemical reaction takes place. There is a formation and breakdown of bonds when a chemical reaction happens. In an exothermic reaction, energy is always released whereas in endothermic reaction energy is always taken in. The changes that happen chemically are known as chemical changes and that leads to the chemical reaction on the body of the matter. Energy is involved in chemical change through bond formation and breaking. In the case of exothermic reactions, there has been the release of energy and in endothermic reactions, energy is absorbed. This is an important point to remember.