Test: Changes Around Us - Class 6 MCQ

Processes (i) and (ii) involve absorption of heat energy while processes (iii), (iv) and (v) involve evolution of heat energy.

Sharpening of pencil - Physical, irreversible change
Evaporation of water - Physical, reversible change
Photosynthesis - Chemical, irreversible change
Rusting of iron - Chemical, irreversible change

:Blowing of a balloon and drying of wet clothes are examples of physical, reversible changes as both these changes do not involve any change in the composition and can be reversed. Tearing of paper and cutting of tree are physical changes that cannot be reversed. Hardening of cement and baking of a cake involve chemical reactions, and are thus chemical changes. Sunrise-sunset and low-high tides are examples of periodic changes as these changes occur at regular intervals.

Decomposition of calcium carbonate is an endothermic, chemical change as calcium carbonate breaks into calcium oxide and carbon dioxide by absorption of heat. Slaking of lime releases a lot of heat hence, it is an exothermic, chemical change.
Therefore, P should be ‘exothermic’, Q should be 'endothermic' and R should be chemical change.