Question

Question 4

1. Define catalyst.

2. Write any three differences between physical and chemical change.

(c) Classify the following processes into physical or chemical changes.
baking of bread, switching of an electric bulb, curdling of milk, dissolving sodium chloride in water, photosynthesis, rusting of iron, evaporation of water, formation of dew, sublimation of camphor, burning of charcoal or LPG, clotting of blood, crystallization of sugar, ripening of fruit, cooking of vegetables, melting of wax.

Answer 1

1. Substances that alter the rate of a reaction without itself being consumed, are known as catalysts.

Physical Change	Chemical Change
1. The change takes place only in the state, texture, colour, electrical or magnetic properties or solubility, etc. However, molecular properties (composition) do not change,	1. The change takes place in the state, texture, colour, electrical or magnetic properties along with the change in its molecular properties (i.e. its molecular arrangement changes).
2. The specific properties of the substance remain unaltered after the physical change.	2. The specific properties of the substance change completely after the chemical change
3. No new substances are produced.	3. New substances are produced.

(c) Physical Changes:- switching of an electric bulb, dissolving sodium chloride in water, evaporation of water, formation of dew, sublimation of camphor, crystallization of sugar, melting of wax.

Chemical changes:- baking of bread, curdling of milk, photosynthesis, rusting of iron, burning of charcoal or LPG, clotting of blood, ripening of fruit, cooking of vegetables.