Change is the law of life. Everything changes over a period of time. Have you ever thought, what is going to happen if everything remains same around us? It will be a disaster if everything gets stuck in one place because nothin will progress in the absence of change. Sun moves, planets travel, rivers flow, plants grow, animals die , these are law of nature. However, not every change is useful to us. Some changes can cause loss and damage to earth. For example, watch an iron nail left opened for 6 months. What happens to the iron? It attracts rust. There are so many such changes in the world which are harmful. In this lesson we will refresh our knowledge on changes around us with the help of question answers.
1. To walk through a water logged area, you usually shorten the length of your dress by folding it. Can this change be reversed?
Answer: Yes, this can be reversed and it is very simple .
2. You accidentally dropped your favourite toy and broke it . This is a change you did not want. Can this change be reserved?
Answer: No, unfortunately, this cannot be reversed as we cannot make a toy as original toy out of the broken pieces.
3. Some changes are listed in the following table, For each changes, write in the blank column, whether the change can be reversed or not
Answer:
|
Sl.no |
Change |
Can be reversed (Yes / No) |
|
1 |
The sawing of a piece of wood |
Yes |
|
2 |
The melting of ice candy |
Yes |
|
3 |
Dissolving sugar in water |
No |
|
4 |
The cooking of food |
No |
|
5 |
The ripening of a mango |
No |
|
6 |
Souring of milk |
No |
4. A drawing sheet changes when you draw a picture on it .Can you reverse this change?
Answer: No, because once we use pen for drawing , the drawing sheet cannot be brought back to the original state ,however, the sheet can be reversed if the drawing was made out of pencil.
5. A thick coating of a paste of plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying, to keep the fractured bone immobilised, can the change in POP be reversed?
Answer: No, because POP is made up of a tough material, hence it is not possible to reverse to its original state.
6. Differentiate between a physical change and a chemical change.
Answer: A physical change refers to the change of the physical appearance of the object such as its shape, and size, whereas chemical change causes an alteration in the chemical composition of underlying substances. A chemical change involves the formation of a new substance with different chemical properties and such change is usually irreversible.
7. A bag of cement lying in the open area gets wet due to rain during the night. The next day the sun shines brightly. Do you think the changes, which have occurred in the cement, could be reversed?
Answer: No, these are irreversible chemical changes
8. When you tie your shoe lace , the shape of the lace is changed? Is it a physical or chemical change?
Answer. This is a physical change and it can be reversed.
9. Can we obtain batter from dosa or idly?
Answer. No, we cannot get back the batter from dosa because it is a chemical change and is an irreversible.
10. Define the term reversible and irreversible change.
Answer. Changes that can be reversed are called reversible changes while changes that cannot be reversed back to its original form are irreversible changes. . For example, the glowing of an electric bulb is a reversible change. Milk becoming curd is an irreversible change.
11. What type of change is stretching of a rubber band?
Answer. It is a reversible change
12. The melting of ice is a reversible change. Why?
Answer. Because ice when heated becomes water and the same water can be condensed back into ice by cooling it.
Match the following items given in Column A with that in Column B:
|
Column A |
Column B |
|
(a) Irreversible change |
(i) Needs mixing of two substances |
Answer:
|
Column A |
Column B |
|
(a) Irreversible change |
(vi) No new substance is formed |
Fill in the blanks with appropriate words:
Answers:
True or False statements :
Answer: