# In a reaction

Question.

In a reaction

$A+B_{2} \rightarrow A B_{2}$

Identify the limiting reagent, if any, in the following reaction mixtures

(i) 300 atoms of $A+200$ molecules of $B$

(ii) $2 \mathrm{~mol} A+3 \mathrm{~mol} B$

(iii) 100 atoms of $A+100$ molecules of $B$

(iv) $5 \mathrm{~mol} \mathrm{~A}+2.5 \mathrm{~mol} \mathrm{~B}$

(v) $2.5 \mathrm{~mol} \mathrm{~A}+5 \mathrm{~mol} \mathrm{~B}$

Solution:

A limiting reagent determines the extent of a reaction. It is the reactant which is the first to get consumed during a reaction, thereby causing the reaction to stop and limiting the amount of products formed

(i)According to the given reaction, 1 atom of A reacts with 1 molecule of B. Thus, 200 molecules of B will react with 200 atoms of A, thereby leaving 100 atoms of A unused. Hence, B is the limiting reagent

(ii)According to the reaction, 1 moleof A reacts with 1 moleof B. Thus, 2 moleof A will react with only 2 moleof B. As a result, 1moleof A will not be consumed. Hence, A is the limiting reagent

(iii)According to the given reaction, 1 atom of A combines with 1 molecule of B. Thus, all 100 atoms of A will combine with all 100 molecules of B. Hence, the mixture is stoichiometric where no limiting reagent is present

(iv)1 moleof atom A combines with 1 moleof molecule B. Thus, 2.5 moleof B will combine with only 2.5 moleof A. As a result, 2.5 moleof A will be left as such. Hence, B is the limiting reagent

(v)According to the reaction, 1 moleof atom A combines with 1 moleof molecule B. Thus, 2.5 moleof A will combine with only 2.5 moleof B and the remaining 2.5 moleof B will be left as such. Hence, A is the limiting reagent