Question

9
.
In a reaction 3A + B2 —> A,B2 [NCERT Pg. 20]
If 180 atoms of A and 100 molecules of B react,
then
(1) B is limiting reactant and 100 molecules of
A, B, will be formed
(2) A is limiting reactant and 60 molecules of A,B2
will be formed
(3) A is limiting reactant and 180 molecules of
A, B, will be formed
(4) B is limiting reactant and 60 molecules of A,B2
will be formed.​

Answer 1

(Here, the reaction should be $\[A + {B_2} \to A{B_2}\]$) [Correction]

In the reaction $\[A + {B_2} \to A{B_2}\]$, if 180 atoms of A react with 100 molecules of B, then B is the limiting reactant and 100 molecules of $\[A{B_2}\]$  will be formed. Thus, the correct option is (1).

Explanation:

• A limiting reactant is a substance that is completely consumed in a chemical reaction.
• In the given reaction, $\[A + {B_2} \to A{B_2}\]$, one molecule of $B$ combines with one atom of $A$.
• Therefore, 100 molecules of $B$ will combine with 100 atoms of $A$ to form 100 molecules of $\[A{B_2}\]$.
• 80 atoms of $A$ will be left unconsumed.
• Thus, $B$ is the limiting reactant as it is completely consumed in the reaction.