Physical And Chemical Changes Class-8 Dalal ICSE New Simplified Chemistry

Physical and Chemical Changes Class-8 Dalal Simplified ICSE Chemistry Solutions Chapter-2, Physical and Chemical Changes Dr Viraf J Dalal Middle School Allied Publishers Solutions. Chapter-2. We Provide Step by Step Solutions to Questions and Answers of Dr Viraf J Dalal Middle School Chemistry Allied Publishers. Visit official Website CISCE for detail information about ICSE Board Class-8.

Physical and Chemical Changes Class-8 Dalal Simplified ICSE Chemistry Solutions Chapter-2

Board ICSE
Class 8th
Subject Chemistry
Book Name Dalal New Simplified
Chapter-2 Physical and Chemical Changes
Unit-1 Physical and Chemical Changes
Topic Solution of exercise questions
Session 2023-24

Exercise-1

Physical and Chemical Changes Class-8 Dalal Simplified ICSE Chemistry Solutions Chapter-2

Question: 1. Change – is the law of nature which occurs in everyday life. State when a substance [i.e. matter] undergoes a kind of change.

Answer: Change is the law of nature that occurs in everyday life. A substance [i.e. matter] undergoes a kind of change when- subjected to energy changes.

The matter is said to undergo certain changes when energy is added to the matter or removed from the matter.

Question: 2. Give a reason why – 

a] Freezing of water is a reversible change while burning of a candle -an irreversible change.
b] Change of seasons is a periodic change while change of weather is a non-periodic change.

Answer: a] Freezing of water is reversible change as on heating frozen ice changes to water by heating.
Burning of a candle is irreversible change as on reversing the conditions we can not get candle back out of CO2, water vapours and wax vapours.

b] Change of season is periodic change as it occurs at regular intervals. Change of weather is non-periodic change because it does not occur periodically at regular intervals. Weather can change suddenly and it may rain in the evening.

Question: 3. State which of the following pertain to – chemical changes:

a] Substance retains its identity 
b] The change is permanent 
c] No new substance is formed
d] Is easily reversible 
e] Produces one or more new substances by change in its composition
f] The change is temporary 
g] The composition and properties of the original substance are not altered.

Answer: Chemical changes: (b) The change is permanent.
(e) Produces one or more new substances by a change in its composition.

Question: 4. Give four reasons why burning of a magnesium ribbon in air is considered a chemical changes.

Answer: Burning of a magnesium ribbon is chemical change as It is:

  1. Irreversible change
  2. New product with new properties is formed (MgO)
  3. It is a permanent change
  4. Composition is changed
  5. Energy is required to bring the change.

Question: 5. Compare the energy changes involved during a physical and a chemical change.

Answer: Physical changes are not accompanied by a marked evolution or absorption of heat energy whereas chemical changes are accompanied by evolution or absorption of heat energy and sometimes emission of light energy.

Question: 6. Is change of state of matter – a physical or a chemical change. Give reasons.

Answer: The change of state of a substance does not involve the formation of new molecules. A change in temperature or pressure can reverse the change in state. Therefore, a change in state is a physical change.

Question: 7. State which of the following terms connected with change of state of matter i.e. –

a] Melting              b] Vaporization            c] Condensation                 d] Freezing – pertain to –

i] Conversion of a liquid into a vapour or gas.
ii] Conversion of a liquid into a solid.
iii] Conversion of a solid into a liquid on heating.

Answer:

(b) Vaporization

(d) Freezing

(a) Melting

Question: 8. Potassium chloride is added to water and stirred. A salt solution is obtained which is then boiled leaving behind a residue

a] Is the above change physical or chemical.
b] Name the residue which remains behind after the salt solution is boiled.
c] Is the change reversible or not reversible.
d] Are the composition and properties of the original substance altered.
e] Give a reason why the above experimentation would not be possible, if calcium carbonate is taken, in place of potassium chloride.

Answer: a] Physical change.

b] White residue of potassium chloride.

c] Change is reversible.

d] No, the composition and properties are not altered.

e] When in place of KC1, we take calcium carbonate the above experiment cannot be possible as no new substance with new properties is produced, since CaCo3 is insoluble in water. Boiling will also not work as CaCo3 is in solid form in water.

Question: 9. Give a reason why –

a] Heating a platinum wire is a reversible change but, heating a magnesium wire is an irreversible change.
b] Addition of zinc nitrate to water is a physical change but, addition of zinc to dilute nitric acid is a chemical change.
c] Rusting of iron is a chemical change but, magnetization of iron is a physical change.

Answer: a] Heating a platinum wire, the final product is again platinum wire (as platinum is a noble metal and does not react with air), i.e. no change in composition and is a physical change. Heating magnesium wire forms MgO i.e. composition changes a new substance white powder of magnesium oxide is formed is a chemical change.

b] Zinc nitrate (soluble in water) dissolves in water and is reversible. No change in composition takes place is a physical change whereas zinc reacts with dil. nitric acid to produce H2 gas which gets oxidized to water by nitric acid (oxidizing agent) and hence is a chemical change.

c] Rusting of iron is a chemical change as composition changes, the reddish-brown flaky powder is formed with new properties and is irreversible, permanent change but magnetization of iron is temporary and reversible change with no change in composition is a physical change.

Question: 10. Select the chemical changes from the following list of changes –

a] Vaporization of water into water vapour.
b] Boiling of milk.
c] Respiration in mammals 
d] Rotting of eggs.
e] Drying of a fruit
f] The carbon cycle.
g] Occurrence of lightening
h] Breaking of glass
i] Butter turning rancid
j] Glowing of an electric bulb
k] Crystallization of a salt from its solution
l] Change of seasons 
m] Preparation of carbon dioxide from calcium carbonate & dilute hydrochloric acid.

Answer: a] physical change

b] physical change

c] chemical change

d] chemical change

e] physical change

f] physical change

g] chemical change

h] physical change

i] chemical change

j] physical change

k] physical change

l] physical change

m] chemical change

—: End of Physical and Chemical Changes Class-8 Dalal Simplified ICSE Chemistry Solutions Chapter-2 :—

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5 thoughts on “Physical And Chemical Changes Class-8 Dalal ICSE New Simplified Chemistry”

  1. Thanks! It is a very good site. My exams are going on and I can check my answers from here….. Thank you very much…..

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