Changes around us
Revision
soft and is beaten to a desired shape. What kind of changes
are observed in this process– reversible or irreversible?
2. Can we reverse the following changes? If yes, suggest the name
of the method.
(a) Water into water vapour
(b) Water vapour into water.
(c) Ice into water.
(d) Curd into milk.
3. Which of the following changes cannot be reversed?
(a) Blowing of a balloon
(b) Folding a paper to make a toy aeroplane
(c) Rolling a ball of dough to make roti
(d) Baking cake in an oven
(e) Drying a wet cloth
(f) Making biogas from cow dung
(g) Burning of a candle
4. Give one example in each case
(a) Change which occurs on heating but can be reversed.
(b) Change which occurs on heating but cannot be reversed.
(c) Change which occurs on cooling but can be reversed.
(d) Change which occurs on mixing two substances, but
can be reversed.
(e) Change which occurs on mixing two substances, but
cannot be reversed.
5. Identify the changes as physical or chemical changes
- burning wood
- souring milk
- mixing acid and base
- digesting food
- cooking an egg
- heating sugar to form caramel
- baking a cake
- rusting of iron
- crumpling a sheet of aluminum foil
- melting an ice cube
- casting silver in a mold
- breaking a bottle
- boiling water
- evaporating alcohol
- shredding paper
- sublimation of dry ice into carbon dioxide vapour
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