Class 6 - Chemistry - Changes around us
To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?
Yes, it can be reversed by unfolding the dress.
You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?
No, it cannot be reversed, so it is an irreversible change.
Some changes are listed in the following table.
For each change, write in the blank column, whether the change can be reversed or not.
A drawing sheet changes when you draw a picture on it. Can you reverse this change?
If the picture is drawn with a pencil, then it can be erased; hence change can be reversed. But if the picture is drawn with colours,
the change cannot be reversed.
Give examples to explain the difference between changes that can or cannot be reversed.
Examples of Reversible Changes:
Example of Irreversible Changes:
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?
No, the change in plaster of Paris cannot be reversed. 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.
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?
Due to water, cement hardens and its composition changes. Since it is a chemical change therefore it cannot be reversed.