Question

Which of the following are chemical changes?
(i) Decaying of wood
(ii) Burning of wood
(iii) Sawing of wood
(iv) Hammering of a nail into a piece of wood

• A. (i) and (ii)
• B. (ii) and (iii)
• C. (iii) and (iv)
• D. (i) and (iv)
  

Answer 1

The correct option is A

(i) and (ii)

1. Chemical change- A chemical change results from a chemical reaction, while a physical change is when matter changes forms but not chemical identity.
2. The five conditions of chemical change: colour change, formation of a precipitate, formation of a gas, odour change and temperature change.
3. Example - rusting of iron.
4. Physical changes are those in which the physical properties of the substances change. It is reversible and no new product is formed. Example: Conversion of water into steam.

Explanation of correct option:

Decaying of wood:

1. There is a change in the chemical composition of the wood.
2. It's a chemical change.

Burning of wood:

1. When wood is burned, there is the production of carbon dioxide, water vapour and ash.
2. It is a chemical reaction.

Since decaying and burning wood is a chemical change thus option (a) is correct.

Explanation of incorrect options:

Sawing of wood:

1. The physical characteristics like the shape and size change.
2. The chemical composition of the wood doesn't change.
3. It's a physical change.

Hammering of the nail into a piece of wood:

1. Only the shape of the wood changes.
2. There is no change in its chemical composition thus it's a physical change.

Since sawing of wood and hammering of the nail are physical changes thus options (b), (c) and (d) are incorrect.

Hence, option (a) is the correct option.