Question 23

# In a reaction A + B2 → AB2 Identify the limiting reagent, if any, in the following reaction mixtures.(i) 300 atoms of A + 200 molecules of B(ii) 2 mol A + 3 mol B(iii) 100 atoms of A + 100 molecules of B(iv) 5 mol A + 2.5 mol B(v) 2.5 mol A + 5 mol B

while solving the problems relating to chemical equation,the reactant react according to the balanced chemical equation.Quite often, one of the reactant is present in lesser amount while the other may be present in higher amount.The reactant which is present in lesser amount is known as limiting reactant or reagent.

(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.Here atom B is in lesser amount(200)

(ii) According to the reaction, 1 mol of A reacts with 1 mol of B. Thus, 2 mol of A will react with only 2 mol of B. As a result, 1 mol of 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 mol of atom A combines with 1 mol of molecule B. Thus, 2.5 mol of B will combine with only 2.5 mol of A. As a result, 2.5 mol of A will be left as such. Hence, B is the limiting reagent because B is less as compared to A

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