Changes Around Us Important Questions

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Questions:

Generic 3

5 x 3 = 15

Some bags of cement lying on the floor get wet due to the leakage of tap water in the room. The next day, they are kept in the sunshine. Do you think the changes, that have occurred in the cement could be reversed?

Rohit puts a few drops of alcohol on the back of his hand. The alcohol disappears and his hand feels cool. Why does this happen?

How the iron blade in these tools is fixed to the wooden handle?

Melting of wax can be reversed whereas burning of wax cannot be reversed. Explain.

You accidently dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?

Multiple Choice Question

5 x 1 = 5

Breaking of toy is a

(a)

Reversible change

(b)

Periodic change

(c)

Irreversible

(d)

All of these

Rolling of chapati and baking of chapati are the changes that:

(a)

Can be reversed

(b)

Can not be reversed

(c)

Can be reversed and can not be reversed respectively

(d)

Can not be reversed and can be reversed respectively.

Which of the following changes can not be reversed?

(a)

Hardening of cement

(b)

Freezing of ice cream

(c)

Opening a door

(d)

Melting of chocolate

Iran rim is made slightly smaller than the wooden wheel. The rim is usually heated before fixing into the wooden wheel because on heating the iron rim

(a)

expands and fits onto the wooden wheel

(b)

contracts and fits onto the wooden wheel

(c)

no change in the size takes place

(d)

expands first, then on cooling contracts and fits onto the wooden wheel

10.

Which of the following changes cannot be reversed?

(a)

Hardening of cement

(b)

Freezing of ice cream

(c)

Opening a door

(d)

Melting of chocolate

Fill up / 1 Marks

2 x 1 = 2

11.

Changing of bread into toast is an ______ change because you can not convert the toast into bread again

12.

Change in weather takes place due to____________ of the sun.

Generic 2

5 x 2 = 10

13.

What are periodic and non-periodic changes? Give examples

14.

Explosion of a cracker is a chemical change. Explain

15.

You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?

16.

Melting of wax is a irreversible change. Is it correct?

17.

Look at the figures given below, which show three situations (a) burning candle (b) an extinguished candle (c) melting wax.

Which of these shows a reversible change and why?

Generic 5

5 x 5 = 25

18.

In the given table, check whether the given changes can be reversed or not.

Change	Can be reversed
Raw egg to boiled egg	Yes/No
Batter to Idli
Wet clothes to dry clothes
Woollen yarn to knitted sweater
Grain to its flour
Cold milk to hot milk
Straight string to a coiled string
Bud to flower
Milk to paneer
Cowdung to biogaes
Stretched rubber band to its
normal size
Ice cream to molten ice cream

19.

It was Paheli's birthday, her brother Simba was helping her to decorate the house for the birthday party and their parents were also busy making other arrangements. Following were the activities going on at Paheli's home:
(a) Simba blew balloons and put them on the wall.
(b) Some of the balloons got burst.
(c) Paheli cut colourful strips of paper and put them on the wall with the help of tape.
(d) She also made some flowers by origami (paper folding) to decorate the house.
(e) Her father made dough balls.
(f) Mother rolled the dough balls to make puries.
(g) Mother heated oil in a pan.
(h) Father fried the puries in hot oil.
Identify the activities at Paheli's home, as those that can be reversed and those, which cannot be reversed.

20.

Paheli mixed flour and water and
(a) made a dough,
(b) rolled the dough to make a chapati,
(c) baked the chapati on a pan,
(d) dried the chapati and ground it in a grinder to make powder.
Identify the changes (a) to (d) as the changes that can be reversed or that cannot be reversed.

21.

Conversion of ice into water and water into ice is an example of change which can be reversed. Give four more examples where you can say that the changes can be reversed.

22.

Give one example in each case.
(a) Change which occurs on heating but can be reversed.
(b) Change which occurs on heating but cannot be reversed.
(c) Change which occurs on cooling but can be reversed.
(d) Change which occurs on mixing two substances but can be reversed.
(e) Change which occurs on mixing two substances but cannot be reversed.

True or False

1 x 1 = 1

23.

Salt can be obtained from sea water by the process of evaporation

(a)

False

(b)

True

1 Marks

2 x 1 = 2

24.

The shape of a paper sheet changes when you make an aeroplane from it. Can you reverse this
change?

25.

Is making an omelette reversible or irreversible change

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Answers Key:

Generic 3

5 x 3 = 15

Cement bags are converted into a hard mass due to the chemical reaction with water. Anew product is formed, which has entirely different properties. So it being a chemical changes cannot be reversed.

It happens because, the heat energy required for the change is provided by the body

To fix the handle, the ring is heated and it becomes slightly large in size. Then, the handle easily fits into the ring. When the ring cools down contracts and fits tightly onto the handle.

Melting of wax is a reversible change because solid wax melts on heating and melted wax becomes solid on cooling. Melting of wax is a change which can be reversed, whereas burning of wax is an irreversible change we cannot combine all the products of burning of wax to get back the original candle. Therefore, burning of wax is a Change which cannot be reversed.

No, this change cannot be reversed. Because breaking of a toy is an irreversible change, we cannot regain the same toy.

Multiple Choice Question

5 x 1 = 5

(d)
expands first, then on cooling contracts and fits onto the wooden wheel

10.

(a)
Hardening of cement

Fill up / 1 Marks

2 x 1 = 2

11.

()
irreversible.

12.

()
heat

Generic 2

5 x 2 = 10

13.

Periodic change : A change that repeats after a definite time interval is known as periodic change, e.g., phases of moon, heart-beat, etc.
Non-periodic change : A change that does not repeat again and again after a regular interval of time is known as non-periodic change, e.g., earthquake, flood and so on.

14.

When we burn a cracker, it explodes. Heat, light and smoke come out after explosion. Many new products are formed. Hence, it is a chemical change.

15.

No, this change can not be reversed

16.

No, melting of wax is a reversible change because solid wax melts on heating and melting wax becomes solid on cooling

17.

Melting of wax in (c), which on cooling, changes back to solid wax but burning candle and an extinguished candle show chemical irreversible change.

Generic 5

5 x 5 = 25

18.

Change	Can be reversed
Raw egg to boiled egg	No
Batter to Idli	No
Wet clothes to dry clothes	Yes
Woollen yarn to knitted sweater	Yes
Grain to its flour	No
Cold milk to hot milk	Yes
Straight string to a coiled string	Yes
Bud to flower	No
Milk to paneer	No
Cowdung to biogas	No
Stretched rubber band to its	Yes
Ice cream to molten ice cream	Yes

19.

Reversed changes are as follows:
(a) Simba blew balloons and put them on the wall.
(d) Making of some flowers by origami (paper folding) to decorate the house.
(e) Her father made dough balls.
(f) Mother rolled the dough balls to make puries.
(g) Mother heated oil in a pan.
Changes that cannot be reversed are as follows:
(b) Some of the balloons got burst.
(c) Paheli cut colourful strips of paper and put them on the wall with the help of tape.
(h) Father fried the puries in hot oil

20.

(a) Made a dough this change cannot be reversed
(b) Rolled the dough to make a chapati. This change can be reversed.
(c) Baked the chapati on a pan, this change cannot be reversed.
(d) Dried the chapati and ground it in a grinder to make powder, this change cannot be reversed.

21.

Changes that can be reversed are called reversible changes.
Some examples are as follows:
(i) Melting of wax
(ii) Folding of a paper
(iii) Knitting of a sweater
(iv) Inflating of a tyre

22.

The example of each case is as follows:
(a) Heating of an iron rod
(b) Baking of chapati
(c) Formation of ice from water
(d) Formation of salt solution
(e) Mixing of cement and water

True or False

1 x 1 = 1

23.