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Published on: 26/09/2019
Changes Around Us
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Questions + Answers key
Take MCQ Science Test

1.
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 |
2.
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.
3.
When a candle burns, both physical and chemical changes occur. Explain.
4.
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.
5.
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.
6.
Differentiate between physical and chemical changes. Give two examples.
1.
| 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 |
2.
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
3.
Physical changes A candle is made up of wax. We take a small candle and measure its length with scale. Now fix this candle on a tile kept on table and light it with burning matchstick. Allow the candle to burn for some time. Now we absorb melting wax comes to side of candle or table. This wax is reversible and we can used this wax.
Chemical changes The wax near the flame burns and gives new substance like carbon dioxide, carbon soot, water vapours, heat and light.
4.
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
5.
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
6.
| S.No | Physical change | Chemical change |
|---|---|---|
| 1 | Only physical properties like colour volume, etc change. | The chemical composition and chemical properties of the reacting substances undergo a chang |
| 2 | No new substance is formed. Examples: (i) Conversion of water into ice. (ii)Tearing of paper. |
One or more new substances are formed Examples: (i) Burning of cooking gas, (ii)Ripening of fruits. |
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