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Question -

In a reaction

A + B2 → AB2

Identify the limiting reagent, if any, in the followingreaction 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



Answer -

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

(i) According to the given reaction, 1 atom of A reacts with1 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 mol of A reacts with 1mol of B. Thus, 2 mol of A will react with only 2 mol of B. As a result, 1 molof B will not be consumed. Hence, A is the limiting reagent.

(iii) According to the given reaction, 1 atom of Acombines with 1 molecule of B. Thus, all 100 atoms of A will combine with all100 molecules of B. Hence, the mixture is stoichiometric where no limitingreagent 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 ofA will be left as such. Hence, B is the limiting reagent.

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

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