Class-7 Dalal Simplified Physical and Chemical Changes ICSE Chemistry Solutions

Class-7 Dalal Simplified Physical and Chemical Changes ICSE Chemistry Solutions Dr Viraf J Dalal Middle School Allied Publishers Solutions. Chapter-2. We Provide Step by Step Solutions of Exercise/Lesson -2  Physical and Chemical Changes with Objective Type Questions, Fill in the blanks and Give reason , Match the following of Dr Viraf J Dalal Middle School Chemistry Allied Publishers. Visit official Website CISCE for detail information about ICSE Board Class-7.

Class-7 Dalal Simplified Physical and Chemical Changes ICSE Chemistry Solutions Cha- 2


EXERCISE-2

Question 1.
Change is the law of nature and occur in our everyday life, at all times and in all places.

Differentiate between the following changes with a suitable example.

  1. Desirable and undesirable change
  2. Periodic and non-periodic change
  3. Slow and fast change
  4. Natural and man-made change
  5. Reversible and irreversible change.

Answer 1:
(a) Desirable and undesirable change

Desirable Change Undesirable change
Changes that take place naturally or artificially and produce  desirable changes. Changes that take place naturally or artificially and produce undesirable changes.
Exa- ripen of fruit ,Rainfall on crops –  milk to curd – Growth of plants., Exa- – – breaking of goods,Rotting of fruits – Falling of trees – storm , floods


(b) Periodic and non-periodic change

Periodic Change Non-periodic change
Changes that take place at regular intervals of time . Changes which take place irregularly
Ex- Change of seasons –  Day turning into night Ex -Rusting of iron ,storm , Thunder and lightning


(c) Slow and fast change.

Slow Changes Fast Changes
Changes that take place very slowly, . Changes that take place quickly .
Ex – – Growith of trees – rusting –  soil formation Ex – – Burning wood – Bursting of crackers – chemical reaction


(d) Natural and man-made change

Natural Changes Man-made Changes
Changes that take place naturally and not artificially are natural changes. Changes that do not take place naturally but are artificial and man-made are man-made changes.
Ex- – Growth of living Ex – –  Fuel to gas – Burning candle


(e) Reversible and irreversible change.

Reversible Changes Irreversible Changes
Changes which are not permanent and can be reversed by another change are reversible changes. Changes which are permanent and cannot be reversed by any change.
Exa – –  Melting of ice – Ex – -ripening of fruit

Question 2.

Differentiate between a physical change and a chemical change with reference to –

  1. Nature of change i.e. temporary and reversible or permanent and irreversible.
  2. Formation of products.
  3. Energy change taking place during the respective change.

Answer 2:

Physical change Chemical change
(a) This change is temporary and reversible. (a) These changes are permanent and irreversible.
(b) There is no formation of new products. (b) There is formation of new products.
(c) There is no energy change in these changes. (c) Energy is either absorbed or evolved in these changes.
Ex – evaporation of water Ex – ripening of fruit

Question 3.

Give three reasons why melting of wax, is considered a physical change while burning of a candle, a chemical change.
Answer 3:

melting of wax, is considered a physical change

Melting of wax is temporary and wax can settle again on cooling and turns into a solid. Hence, the change is only physical and the state of matter changes.

burning of a candle, a chemical change

Burning of the candle is permanent because once it is burnt it cannot be converted into the candle. A new product is also formed with a composition different from candle. Hence it is a chemical change.

Question 4.
State the observations seen, when milk in a dish is kept aside for a few hours or more. Is the change which occurs – a physical change or a chemical change. Give reasons.
Answer 4:
When milk is kept aside in a dish for a few hours or more, it is observed that milk turns into curd. This change is chemical as it is permanent and cannot be reversed. A new product i.e. curd is also formed.

Question 5.
State what is meant by the term – inter conversion of matter. Is inter conversion of matter a physical change or a chemical change.
Answer 5:

The change of state of matter from one state to another state and back to the original state of matter is known as inter-conversion of matter.

This change is physical because it is not permanent and reversible.

Question 6.
Ice kept in a beaker, slowly melts and turns into water. The water in the beaker on solidification Le. freezing turns back to ice. Give four reasons why the change from ice to water and water back to ice is considered a physical change.
Answer 6:

Both Melting of ice and freezing of water are physical changes because:

  1. These change  are temporary
  2. They are reversible i.e. ice turns into water and water again turns into ice.
  3.  no new products formed
  4. The composition and properties of water are not altered.

Question 7.
Explain the term – ‘sublimation’. Is sublimation of naphthalene – a physical or a chemical change. Give reasons.
Answer 7:

The conversion of a solid directly to gaseous form and on cooling back to the solid-state is sublimation.

Sublimation of naphthalene is a physical change because the state of matter changes.

Question 8.
Ammonium chloride is also a sublimable solid. Give a reason why sublimation of ammonium chloride involves a physical and a chemical change.
Answer 8:
Sublimation of ammonium chloride – [NH4C1] On heating, this sublimes and dissociates into ammonia  [NH3] and hydrochloric acid HCl, and recombine on cooling to obtain   – NH4C1
ICSE Solutions for Class 6 History and Civics - Physical and Chemical Changes-09
Dissociation – is a chemical change. Hence, sublimation of such substances involves both – a physical and a chemical change.

Question 9.
State why addition of sodium chloride to water is considered a physical change, while addition of dilute sulphuric acid to zinc is considered a chemical change.
Answer 9:

When water is added to sodium chloride, there is no new product formed, hence it is a physical change.

When dilute sulphuric acid is added to zinc, a new product zinc sulphate is formed, hence it is a chemical change.

Question 10.
Photosynthesis is a natural process by which green plants manufacture food in the presence of sunlight.

  1. Are any new products formed during the above process.
  2. Can the change be reversed or is it irreversible
  3. State the conclusions which can be drawn, to represent photosynthesis as a physical or a chemical change.

Answer 10:

  1. The change is permanent and new products are formed like glucose and oxygen.
  2. The change is irreversible.
  3. It is a chemical change because carbon dioxide and water cannot be obtained back from glucose and oxygen.

Question 11.
Give reasons why – separation of mixtures e.g. iron from a mixture of iron and sulphur is a physical change, but heating a mixture of iron and sulphur is considered a chemical change.
Answer 11:

Why separation of iron from a mixture of iron and sulphur is a physical change,

  • The properties of iron and sulphur do not change when they are separated.
  • There is no formation of a new product in this change.
  • There is no change in the heat energy level of the mixture.
  • The change is temporary and reversible as iron and sulphur can be mixed again.

Why heating a mixture of iron and sulphur is a chemical change.

  • There are changes in properties of both on heating, they lose their magnetic power.
  • A new substance, iron sulphide is formed.
  • The heat energy is released when the iron and sulphur mixture is heated. The test tube becomes red hot.
  • The change is permanent, which means it cannot be reversed.

Question 12.
Explain in brief the involvement of energy in – physical and chemical changes.
Answer 12:
Involvement of energy during physical / chemical changes

In physical changes, energy is used to change the state of matter.

In chemical changes, energy is released when there is decomposition of a substance and absorbed while forming a new substance.


Objective Type Questions

Physical and Chemical Changes Class-7 Dalal ICSE New Simplified Dr Viraf J Dalal Middle School Allied Publishers Solutions. Chapter-2

Question- 1. 

Fill in the blanks with the appropriate words for each of the statements given below:

  1. Germination of seeds is considered a _____ reaction.
  2. If a change is permanent & irreversible it is considered a_ change.
  3. Heating a piece of iron is considered a _____ change while heating a piece of coal (carbon) is considered a _____ change.
  4. Chemical changes may involve the exchange of energy in the form of ____ and ____
  5. Change of milk into curd is a _______ change.

Answer-1

  1. Chemical
  2. Chemical
  3. Physical
  4. Light and heat
  5. Desirable

Question -2. 

State whether the following statements are true or false. If false write – the correct statement.

  1. Desirable changes are meaningful, while undesirable changes are unfavourable.
  2. During physical changes, the composition of the original substance is not altered, but the properties of the original substance are altered.
  3. During a chemical change the composition of the original substance is not altered and the change is irreversible
  4. Melting of butter and wax are examples of chemical changes.
  5. Melting of ice is an exothermic, irreversible chemical change.

Answer-2

  1. Desirable changes are meaningful, while undesirable changes are unfavourable.
    True.
  2. During physical changes, the composition of the original substance is not altered, but the properties of the original substance are altered.
    True.
  3. During a chemical change the composition of the original substance is not altered and the change is irreversible.
    False. During a chemical change the composition of the original substance is altered and the change is irreversible.
  4. Melting of butter and wax are examples of chemical changes.
    False. Melting of butter and wax are examples of physical changes.
  5. Melting of ice is an exothermic, irreversible chemical change.
    False. Melting of ice is an endothermic, reversible physical change.

Question-3. 

Match the examples of changes in List I with the correct.

List I List II
1. Expansion of a steel rod on heating A.Physical
2. Rotting of eggs B.Chemical
3. Milk turning sour
4. Tarnishing of copper
5. Separation naphthalene from a mixture of naphthalene and sodium chloride


Answer- 3:

  1. .Physical
  2. B.Chemical
  3. B.Chemical
  4. B.Chemical
  5. .Physical

Question-4. 

Fill in the blanks with the correct words for each of the statements given below:

  1. Sublimation is ______ a change of state of matter.
  2. Sublimation involves a ______ change.
  3. During sublimation, a solid on heating turns directly into _____ and on cooling back to _____
  4. Ammonium chloride, a sublimable sold undergoes _______ on heating.
  5. Sublimation of iodine is an example of _______ change.

Answer-4

  1. Sublimation is considered a change of state of matter.
  2. Sublimation involves a physical change
  3. During sublimation a solid on heating turns directly into vapour and on cooling back to solid.
  4. Ammonium chloride, a sublimable solid undergoes dissociation on heating.
  5. Sublimation of iodine is an example of physical change

Question-5. 

Name the following:

  1. The product obtained during ‘photosynthesis’ – which is a chemical change.
  2. The term involved in the change of state from – ”water to ice’ – which is a physical change.
  3. The final product of the physical change involved during ‘melting of a piece of wax’
  4. The type of change i.e. physical or chemical involved – ‘during respiration in human beings.’
  5. The type of change i.e. physical or chemical involved – ‘when a substance undergoes a change in state, colour or size.

Answer-5

  1. Glucose and oxygen
  2. Freezing point
  3. Wax
  4. Chemical change
  5. Chemical change

.– : End of Physical and Chemical Changes Class-7 Dalal Simplified Solutions :–


Return to –  Dalal Simplified Chemistry for ICSE Class-7 Solutions

Thanks

Share with your friends. 

You might also like
Show Comments (2)