Physical and Chemical Changes
A drawing sheet changes when you draw a picture on it. Can you reverse this change?
How does curd made? Is this change reversible?
A small quantity of curd is added to warm milk. The milk is stirred and is set aside undisturbed for a few hours at a warm place. In a few hours, the milk changes into curd.
Curd formed from milk cannot be changed into milk again. So, this an irreversible(cannot be reversed)change.
A drawing sheet changes when you draw a picture on it. Can you reverse this change?
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?
Can you say deforestation is an irreversible or reversible change?
Some common changes are given in table. Which of these changes do you think can be reversed? Change Can be reversed (i) Raw egg to boiled egg Yes/No (ii) Batter to idli (iii) Wet clothes to dry clothes (iv) Woolen yarn to knitted sweater (v) Grain to its flour (vi) Cold milk to hot milk (vii) Straight string to a coiled string (viii) Bud to flower (ix) Milk to paneer (x) Cow dung to biogas (xi) Stretched rubber band to its normal size (xii) Melting of ice-cream
Melting of ice is a
Rolling of chapati and baking of chapati are the changes that
Burning of paper and formation of curd are reversible changes.
Give reasons: Dissolving salt in water is a reversible change.