Question

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

Answer 1

(i) According to the reaction, 1 atom of A reacts with 1 molecule of B. 

∴200 molecules of B will react with 200 atoms of A, thereby leaving 100 atoms of A unreacted. Hence, B is the limiting reagent. 

(ii) According to the reaction, 1 mol of A reacts with 1 mol of B. 

∴ 2 mol of A will react with only 2 mol of B leaving 1 mol of B. Hence, A is the limiting reagent. 

(iii) 1 atom of A combines with 1 molecule of B. 

∴ All 100 atoms of A will combine with all 100 molecules of B. Hence, the mixture is stoichiometric and ther is no limiting reagent. 

(iv) 1 mol of atom A combines with 1 mol of molecule B. 

∴ 2.5 mol of B will combine with only 2.5 mol of A. and 2.5 mol of A will be left unreacted. Hence, B is the limiting reagent.

(v) 1 mol of atom A combines with 1 mol of molecule B. 

∴ 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.

Hence, A is the limiting reagent