Question

The gas we use in the kitchen is called liquified petroleum gas (LPG).In the cylinder, it exists as liquid. When it comes out of the cylinder it becomes a gas (Change A) then it burns(Change B).
Choose the correct one:
A) Process A is chemical change.
B) Process B is chemical change.
C) Both these processes are chemical changes.
D) None of these processes are chemical changes.

Answer 1

Hint: In process A, there are no new substances formed. In process B, there are new substances formed like carbon dioxide, heat, light, etc.

Complete step by step answer:
-If its physical form (solid, liquid, or gas) changes from one form to another then it is a physical change. If the reactants are converted into products then it is a chemical change.
-If the reaction gives different products at different temperatures then the reaction depends on the temperature.

-Let us discuss the question now.
-When the liquid comes out of the cylinder as gas, there are no new substances formed. There is a change of state in the matter. This change of state is called a physical change and is thus a reversible reaction. Hence, the process is never a chemical change.
-But, when this gas is burnt then new products are formed. This can be explained with the reaction:
Gas $\dfrac{\text { Burning }}{\longrightarrow} \mathrm{CO}_{2}+$ heat $+$ light $+$ other substances

-This reaction is completely irreversible as carbon dioxide once released cannot be back into the gas. Thus, it is a chemical change. The process is a chemical change.
So, the correct answer is “Option B”.

Note: Gas cylinders are very explosive in nature. So while lighting the gas, we must be very careful and must always follow safety rules to avoid accidents and damages.