Question

In a reaction given below:
$A+B_{2} \longrightarrow AB_{2}$
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

"As per as the chemical reaction is considered, if two reactants are present, consider it as A and B. If reactant A is present higher amount compared to the reactant B, which is of lower amount. Then reactant B is called the "limiting reagent".

$A\quad +\quad B_{2}\quad  \longrightarrow\quad  AB_{2}$

As per as the above equation is consider, 1 atom of A reacts with 1molecule of B to give the products.  

i) "300 atoms" of A reacts with "200 molecules" of B to give product. Here, "200 molecules" of B reacts with 200 atoms A and "100 atoms" of reactant is left. Hence, here the lower concentration reactant B is called the "limiting reagent".

ii) 2 mole of reactant A reacts with 3 mole of reactant B to give products. Here 2 mole of A reacts with 2 mole of B and 1 mole of reactant B is left. Hence here the lower concentration reactant A is called the "limiting reagent".

iii) "100 atoms" of A reacts with "100 molecules" of B. Here in the case the reaction is stoichiometric. In such reactions no "limiting reagent" is present.

iv) 2.5 mole of A reacts with 2.5mole of B to give product. The 2.5mole of A remain left. So here B is the "limiting reagent".

v) 2.5 mole of A reacts with 2.5 mole of B to give product. Here the 2.5 mole of B is remain left. So A is the "limiting reagent"."