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
(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.
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
(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.
Exercise Objective Type Questions
(ICSE Class-8th Physical and Chemical Changes Essential Chemistry Ch-2 Bharti Bhawan)
Page 17
Choose the correct option.
Question 1
Which of the following is not a reversible change?
(a) The change of water into water vapour
(b) The cooling of a hot iron
(c) The condensation of sulphur vapour
(d) The burning oft LPG
Answer :
(d) The burning oft LPG
Question 2 ICSE Class-8th Essential Physical and
Which of the following is a periodic change?
(a) The change of the phases of the moon
(b) The charring of sugar
(c)The curdling of milk
(d) The clotting of blood
Answer :
(a) The change of the phases of the moon
Question 3
During which of the following changes are no new substances formed ?
(a) Photosynthesis
(b) Sublimation
(c) Respiration
(d) Burning
Answer :
(b) Sublimation
Question 4
In which ot the following processes is light absorbed?
(a) Sublimation
(b) Burning
(c) Photosynthesis
(d) Rusting
Answer :
(c) Photosynthesis
Question 5
Which of the following is an exothermic change?
(a) The melting of ice
(b) The freezing of water
(c) The vaporisation of water
(d) The dissolution of glucose in water
Answer :
(b) The freezing of water
Question 6 ICSE Class-8th Essential Physical and
Which of the the following is an endothermic change
(a) The slaking of lime
(b) The burning of wood
(c) The melting of iron
(d) Respiration
Answer :
(c) The melting of iron
Fill in the blanks :
1. When a solid dissolves in a liquid, the volume of the liquid … does not change …. (changes/does not change)
2 Photosynthesis is a .. chemical .. change. (physical/chemical)
3. The vaporisation of water is an .. endothermic .. change. (endothermic/exothermic)
4. When burnt, CNG forms carbon dioxide and .. water vapour .. (hydrogen/water vapour)
5. Iron combines with oxygen and .. moisture.. oft the air to form rust. (nitrogen/moisture)
6. The kinetic energy of molecules .. increases .. when a solid melts. (increases/decreases)
Write T for true and F for false for the following statements.
1. A physical change is irreversible. false
2 A chemical change is reversible. false
3. The mass of a substance undergoing a physical change is not altered. true
4. Heat is absorbed when glucose is dissolved in water. false
5. Heat is evolved when concentrated hydrochloric acid is poured into water. true
6. The slaking of lime is an endothermic change. false
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