The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder it exist as a liquid. When it comes out from the cylinder it becomes a gas (Change – A) then it burns (Change – B). The following statements pertain to these changes. Choose the correct one.
(i) Process – A is a chemical change.
(ii) Process – B is a chemical change.
(iii) Both processes A and B are chemical changes.
(iv) None of these processes is a chemical change
NCERT Solutions for Class 7th Science Chapter 6 Physical and Chemical Changes Page 66 Exercise Question 11
Answers
Answer:
The correct answer of this question is option 3, process B is a chemical change.
Explanation:
The process A is occurred due to the change of atmospheric pressure and that's why it is a physical change.
On the other hand,
The process B is occured with the help of the oxygen reaction and new products are created after the combustion and that's why it is a chemical change.
Answer:
The correct answer is (ii) 'Process – B' is a 'chemical change'.
Explanation:
The gas we use in the 'kitchen' is called 'Liquefied petroleum gas' (LPG). In the 'cylinder', it exists as a 'liquid'.
When it 'comes out' from the 'cylinder', it becomes a 'gas' (Change – A) then it 'burns' (Change – B).
Thus Process A is a 'physical change' since Process A involves the change of state of matter from liquid to gas. This is a reversible process, as the gaseous LPG can again be converted to the liquid stage.
However, Process B involves combustion of LPG, which is a chemical change, which 'alters' the properties of the LPG after combustion and is irreversible.