ICSE Class-8th Physical and Chemical Changes Essential Chemistry Ch-2 Bharti Bhawan Publishers

ICSE Class-8th Physical and Chemical Changes Essential Chemistry Ch-2 Bharti Bhawan Publishers. We Provide Step by Step Answer of Objective, Choose the Correct Option ,True False , Fill in the blanks ,Short / Long Answer Type of Exercise-2 Physical and chemical changes. Visit official Website CISCE for detail information about ICSE Board Class-8.

Board ICSE
Publications Bharti Bhawan Publishers
Subject Chemistry 
Class 8th
Chapter-2 Physical and Chemical Changes
Book Name Essential
Topics Solution of Objective, True False , Match the following , Short / Long Answer Type Questions
Academic Session 2021-2022

ICSE Class-8th Physical and Chemical Changes Essential Chemistry Ch-2 Bharti Bhawan Publishers


Exercise Short-Answer Type Questions

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(ICSE Class-8th Physical and Chemical Changes Essential Chemistry Ch-2 Bharti Bhawan)

Page 16

Question 1

What are reversible changes? Which of the two-the vaporisation of water and the burning o paper-is a reversible change.

Answer :  

A reversible change is a change that can be undone or reversed. If you can get back the substances you started the reaction with, that’s a reversible reaction. …Examples of reversible reactions include dissolving, evaporation, melting and freezing

the vaporisation of water is a reversible change.

Question 2

What are irreversible changes? Which of the two-the melting of ice and the growth of a plant an irreversible change?

Answer :  

Irreversible changes are permanent. They cannot be undone. For example you cannot change a cake back into its ingredients again.

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growth of a plant an irreversible change

Question 3

Define a periodic change. Is rusting a periodic change

Answer :  

periodic changes are the changes that tend to repeat or reoccur at the same interval of time periodically. There are infinite examples of a periodic change like a simple pendulum, the change in the position of a simple pendulum can be periodic and sometimes it can also be categorized as cyclic change

No, rusting is not a  periodic change

Question 4

Define a nonperiodic change. Is the swinging of a pendulum a nonperiodic change?

Answer :  

Non-periodic changes are changes which do not occur periodically or at regular intervals. Example: Change of weather

the swinging of a pendulum a periodic change

Question 5

Classify the following into desirable and undesirable changes.

(a) the spoiling of food

(b) The digestion of food

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(c) The rotting of an egg

(d) The decay of a dead animal in open air

Answer :  

(a) the spoiling of food- undesirable changes

(b) The digestion of food- desirable changes

(c) The rotting of an egg –undesirable changes

(d) The decay of a dead animal in open air- desirable changes

Question 6

Define a physical change. Is rusting a physical change?

Answer :  

A physical change is a change to the physical—as opposed to chemical—properties of a substance. They are usually reversible.

No, rusting is not  physical change?

Question 7

Define a chemical change. Is the heating of an electric iron a chemical change?

Answer :  

A chemical change is a change of materials into another, new materials with different properties

No,  the heating of an electric iron is not a chemical change?

Question 8

Classify the following into physical and chemical changes.

………………..

Answer :  

(a) The melting of ice – physical changes

(b) Respiration  –  chemical changes

(c) The cooking of food  – chemical changes

(d) Fermentation  – chemical changes

(e) The evaporation of a liquid  – physical  changes

(f) The sublimation of iodine  –  chemical changes

(g) The dissolving of a solid  – physical changes

(h) The burning of coal  –  chemical changes

(i) The glowing of a bulb  – physical  changes

(j) The freezing of water  – physical changes

(k) The curdling of milk  – chemical changes

(l) Photosynthesis in green plants  –  chemical changes

(m) The condensation of water vapour  – physical  changes

(n) The digestion of food  –  chemical changes

Question 9

Define exothermic and endothermic changes.

Answer :  

An exothermic process is one that gives off heat. This heat is transferred to the surroundings.

An endothermic process is one in which heat has to be supplied to the system from the surroundings.


Exercise Long-Answer Type Questions

(ICSE Class-8th Physical and Chemical Changes Essential Chemistry Ch-2 Bharti Bhawan)

Page 16

Question 1

Give two examples to show that the mass of the individual substance(s) undergoing a chemical change is altered. How do these changes obey the law of conservation of mass?

Answer :  

The mass of the individual substance undergoing a chemical change is altered. For example –
1. When carbon is burnt in air, the amount of carbon is reduced and finally the carbon vanishes. In
fact, all the carbon gets converted to carbon dioxide.
2. If an iron nail is allowed to rust, the mass of the rusted nail is more than that of the original nail.

Question 2

State the differences between physical and chemical changes.

Answer :  

Physical change

1. A physical change is temporary.
2. A physical change is reversible.
3. No new substances are formed in a physical change.
4. In a physical change, the mass of the substance does not change.
Chemical change

1. A chemical change is permanent.
2. A chemical change is irreversible.
3. New substances are formed in a chemical change.
4. The mass of the individual substance undergoing a chemical change is altered

Question 3

Discuss an example to show that physical and chemical changes can occur together.
Answer :  

Physical and chemical changes can happen together. A common example is the burning of a candle.
The following changes occur when a candle burns.
1. The wax under the wick gets heated and melts. The molten wax flows down and solidifies. The
changes in state from solid to liquid and again from liquid to solid are physical changes.
2. A part of the molten wax vaporizers and burns to form new substances-carbon dioxide and
water vapour. This change is irreversible.
So, the burning of wax is a chemical change.

Question 4

Giving one example of each kind, show that a change in energy takes place when a physical or a chemical change occurs.
Answer :  

Example of energy change in a physical change-

Energy changes observed during a change in state. A solid has to be heated in order to melt. In other
words, a solid absorbs heat in order to melt. For example, ice, sulphur, iron ,etc., absorbs heat in order to
melt.
Example of energy change in a chemical change When coal or wood is burnt, both heat and light are emitted. Burning is an exothermic process

Question 5

Explain why there is an energy change in a change of state of matter as well as in a chemical change.

Answer :  

Respiration is the biochemical process in which the cells of an organism obtain energy by combining
oxygen and glucose, resulting in the release of carbon dioxide, water and energy. The change is not
reversible and is, therefore, a chemical change.

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