1. Reversible Changes -
ü The changes described as changes that can be reversed by reversing the action or changing the conditions. Example - rolling of a chapati from dough, : freezing of water etc.
3. How Changes Occur -
ü There are other ways to bring about changes in substances:
ü Mixing two substances together - A small amount of curd is added to warm milk which leads to conversion of that milk into curd. This is an irreversible change.
ü Example - When we add a salt to water it becomes salty but this is a reversible change.
ü Expansion and Contraction - In order to make tools like an axe, the ring of its iron blade is heated which allows it to expand i.e. become larger in size and then is allowed to cool down which makes it contract again i.e. become smaller in size leading to a tight fit of the handle.
NCERT PRACTICE QUESTIONS
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, this change can be reversed..
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. This is physical change by nature.
3. Some changes are listed in the following table. For each change, write in the blank column, whether the change can be reversed or not.
Ans.-
4. A drawing sheet changes when you draw a picture on it. Can you reverse this change?
Ans. - If the drawing is made with a pencil then it can be erased and we will get the original sheet back. So, we can reverse the change. But if the drawing is made with colors or pen, then it cannot be erased. Thus the change cannot be reversed.
5. Give examples to explain the difference between changes that can or cannot be reversed.
Ans. -
6. A thick coating of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilize. Can the change in POP be reversed?
Ans. - No, the change in POP cannot be reversed because plaster of Paris on getting mixed with water changes into a hard mass and form a new compound.
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.- No, these are irreversible chemical changes.
Junior Science Topic - Changes Around Us. Chapter notes, video lectures, power point presentation and NCERT exercise solution. (Class 6, CBSE syllabus, chapter 06)
By - EduPorm India - The Educational Platform
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