1. Some changes, like folding a dress or drawing with pencil, can be reversed by unfolding or erasing. Other changes, like breaking a toy or using a permanent marker, cannot be reversed. 2. Changes like melting ice or dissolving sugar can be reversed by freezing water or evaporating the water. Irreversible changes include sawing wood, cooking food, or the ripening of fruit. 3. Heating materials like tar, rims, or cement causes chemical changes that cannot be reversed, while simply heating items to expand them, like a rim on a wheel, can be reversed by cooling.

1. Change Around Us

2. 1. To walk through a waterlogged area, you
usually shorten the length of your dress by
folding it. Can this change be reversed?
Ans- Yes, we can change it because by folding it
we change the length of dress on unfolding it
we get original dress back.

3. 2. You accidentally dropped your favorite toy and
broke it. This is a change you did not want. Can
this change be reversed?
Ans- No, this change cannot be reversed because
once the thing is broken it is very difficult to get it
back in their original shape.

4. 3. A drawing sheet changes when you draw a
picture on it. Can you reverse this change?
Ans- It is all depends on situations:
By erasing the drawing we can undo the
change. For example, if we draw with the help of
pencil, we can erase the drawing by using an
eraser. Then, it is a reversible change.
If we draw using a pen, we cannot erase the
drawing. Then this change cannot be reversed,
so it is irreversible change.

5. 4. Some changes are listed in the following table.
For each change, write in the blank column,
whether the change can be reversed or not.
Sr.No. Change Can be reversed (Yes/ No)
1. The sawing of a piece of wood
2. The melting of ice candy
3. Dissolving sugar in water
4. The cooking of food
5. The ripening of a mango
6. Souring of milk

6. 5. Give example to explain difference between
changes that can be or cannot be reversed.
Ans- Sr. No Reversible Change Irreversible change
1. Melting of Ice into water.
By freezing the water we
can obtain ice again.
Burning of candle.
2. Folding a paper: By
unfolding it, we can undo
the change.
Bursting of crackers
3. Hot milk to cold milk: By
boiling milk, we can make
it warm.
Cutting of trees.

7. 6. A thick coating of a paste of POP is applied
over the bandage on fractured bone. It
becomes hard on drying to keep the fractured
bone immobilized. Can the change in POP
(plaster of paris) be reversed.
Ans- When water is added to POP, it undergoes a
chemical change. Its composition changes and is
converted into another substance. Since it is a
chemical change, so it cannot be reversed.

8. 7. A bag of cement lying in the open 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?
Ans-Due to water, cement hardens and its
composition changes. Since it is a chemical
change which cannot be reversed.

9. 8. How the iron blade of tools is fixed to the
wooden handle?
Ans- To fix the handle, the ring is heated and it
becomes slightly larger in size(expands) Now
the handle easily fits into the ring.
9. On heating, the rim expands and fits onto the
wheel. Why we poured cold water on rim?
Ans- On pouring the water rim contracts and
tightly fitted to the wheel that’s why we pour
cold water.

10. Recap- Questions
1. Ravi has often noticed that road construction workers
heat a black material(tar) for repairing a road. He want
to know that whether the change is caused in tar, by
heating, Can be reversed?
2. Ice melts when it is heated. What does it change into? Is
it possible to change this water back into ice?
3. What are the changes occur in incense stick after
burning?
4. The changes that occur when tow substances are mixed
together. It can be reversed or not. If yes/no. How?