Chapter 9.3, Problem 3RQ

Interpretation Introduction

Interpretation :

The difference in the limiting reagent problem and other stoichiometry problem must be explained.

Concept Introduction :

A stoichiometry problem deals with the finding of amounts of reactant and product using a balanced chemical equation.

A limiting reagent problem is the one in which one of the reactant is completely consumed and other reagent is in excess.

Answer to Problem 3RQ

In normal stoichiometry problem calculation can be done using the amount of any given substance. But in limiting reagent problem all the calculation must be done based on the amount of limiting reagent available.

Explanation of Solution

Let the following chemical reaction:

  ${\text{N}}_{\text{2}}{\text{(g)+3H}}_{\text{2}}\text{(g)}\to {\text{2NH}}_{\text{3}}\text{(g)}\text{.}$

Let’s consider 5 L nitrogen gas is allowed to reacts with 15 L of hydrogen at STP. Then amount of ammonia which is expected can be calculated based on the amount of hydrogen or nitrogen.

In this case the two reactants are present in required mole ratio (1 mol N₂ needs 3 moles H₂).

In an another case let’s consider 5 L nitrogen is mixed with 10 L of hydrogen, then amount of ammonia expected can’t be calculated from the amount of given nitrogen as nitrogen can’t be consumed completely in this case as sufficient hydrogen (15 L) required for 5 L nitrogen is not provided.