Viraf J. Dalal solutions for New Simplified Middle School Chemistry [English] Class 7 chapter 2 - Physical and Chemical Changes [Latest edition]

Change is the law of nature and occurs in our everyday life, at all times and in all places. Differentiate between the following change with a suitable example.

Desirable and undesirable change.

Change is the law of nature and occurs in our everyday life, at all times and in all places.
Differentiate between the following change with a suitable example.

Periodic and non-periodic change

Change is the law of nature and occurs in our everyday life, at all times and in all places.
Differentiate between the following change with a suitable example.

Slow and fast change.

Change is the law of nature and occurs in our everyday life, at all times and in all places.
Differentiate between the following change with a suitable example.

Natural and man-made change.

What are reversible and irreversible changes ? Give one example for each.

Differentiate between a physical change and a chemical change with reference to – Nature of change is temporary and reversible or permanent and irreversible.

Differentiate between a physical change and a chemical change with reference to – Formation of products.

Differentiate between a physical change and a chemical change with reference to – Energy change taking place during the respective change.

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

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.

State what is meant by the term – interconversion of matter. Is interconversion of matter a physical change or a chemical change.

Ice kept in a beaker, slowly melts and turns into water. The water in the beaker on solidification is 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.

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

Ammonium chloride is also a sublimable solid. Give a reason why the sublimation of ammonium chloride involves a physical and a chemical change.

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.

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

Are any new products formed during the above process.

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

Can the change be reversed or is it irreversible?

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

State the conclusions which can be drawn, to represent photosynthesis as a physical or a chemical change.

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.

Explain in brief the involvement of energy in physical and chemical changes.

Fill in the blank with the appropriate word of the statement given below:

Germination of seeds is considered a __________ change.

Fill in the blank with the appropriate word of the statement  given below:

If a change is permanent and irreversible it is considered a _________ change.

Fill in the blanks with the appropriate words of the statement  given below:

Heating a piece of iron is considered a __________ change while heating a piece of coal [carbon] is considered a ___________ change.

Fill in the blanks with the appropriate words of the statement  given below:

Chemical changes may involve exchange of energy in the form of __________ and _________.

Fill in the blank with the appropriate word of the statement given below:

Change of milk of curd is a _______ change.

State whether the following statement is true or false. If false write the correct statement.

Desirable changes are meaningful, while undesirable changes are unfavourable.

State whether the following statement is true or false. If false write the correct statement.

During physical changes, the composition of the original substance is not altered, but the properties of the original substance are altered.

State whether the following statement is true or false. If false write the correct statement.

During a chemical change the composition of the original substance is not altered and the change is irreversible.

State whether the following statement is true or false. If false write the correct statement.

Melting of butter and wax are examples of chemical changes.

State whether the following statement is true or false. If false write the correct statement.

Melting of ice is an exothermic, irreversible chemical change.

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

Fill in the blank with the correct word of the statement given below:

Sublimation is _______ a change of state of matter.

Fill in the blank with the correct word of the statement given below:

Sublimation involves a __________ change.

Fill in the blanks with the correct words of the statement given below:

During sublimation, a solid on heating turns directly into _________ and on cooling back to __________.

Fill in the blank with the correct word of the statement given below:

Ammonium chloride, a sublimable solid undergoes _________ on heating.

Fill in the blank with the correct word of the statement given below:

Sublimation of iodine is an example of _________ change.

Name the following:

The products obtained during ‘photosynthesis’ – which is a chemical change.

Name the following:

The term involved in the change of state from – ‘water to ice’ – which is a physical change.

Name the following:

The final product of the physical change involved during the ‘melting of a piece of wax’.

Name the following:

The type of change physical or chemical involved – ‘during respiration in human beings’.

Name the following:

The type of change physical or chemical involved – ‘when a substance undergoes a change in state, colour or size’.