Question

Give scientific reason for the following :
1. Burning of paper is a irreversible change.
2. curdling of milk is a chemical change.
3. sublimation is a physical change.​

Answer 1

Explanation:

1.Burning of paper is irreversible as once it is burnt, the chemical composition of paper changes and cannot be brought back to it's previous state

2.Curdling of milk is a chemical change as the bacteria present in it solidify the milk to curd which cannot be brought back to milk. A chemical change occurs which is irreversible

3.Sublimation is a physical change as - first it changes from solid to gas and then gets deposited back to solid, basically it comes back to it's original form without any change in its chemical composition

Answer 2

Explanation:

1. Reason:

We can't get back the paper after burning it, so it is a irreversible change.

2. Reason:

The curd forms because of the chemical reaction between the lactic acid bacteria and casein. So it is a chemical change.

3. Reason:

The term sublimation refers to a physical change of state and is not used to describe the transformation of a solid to a gas in a chemical reaction. For example, the dissociation on heating of solid ammonium chloride into hydrogen chloride and ammonia is not sublimation but a chemical reaction.