Question

How do you identify the limiting reagent for the combination of Balanced Reaction?
$\dfrac{NaOH}{\left( 5\,mol \right)}\,+\,\dfrac{HCl}{\left( 4.5\,mol \right)}\,\,\,\to \,\,NaCl\,+\,\,{{H}_{2}}O$

Answer 1

The limiting reagent is the reactant that gets consumed completely before the reaction ends. This stops the reaction in mid and no further products are produced. For finding out the limiting reagent we first need to find out the number of moles of the reactants given in the reaction. After this we need to find out the molar ratios in which the reactants are reacting, and then perform necessary comparison.

Complete answer:
The given reaction is $\dfrac{NaOH}{\left( 5\,mol \right)}\,+\,\dfrac{HCl}{\left( 4.5\,mol \right)}\,\,\,\to \,\,NaCl\,+\,\,{{H}_{2}}O$
The general balanced reaction is; $NaOH\,+\,HCl\,\to \,NaCl\,+\,{{H}_{2}}O$
From the above balanced reaction, we can interpret that the molar ratio of $NaOH\,and\,HCl\,\,is\,\,1:1$
It means that one mole of $NaOH$will react completely with one mole of $HCl$
Hence $5$moles of $NaOH$will require $5$ moles of $HCl$for the reaction to occur completely.
But in the question, only $4.5$moles of $HCl$is given. It means there is less $HCl$present for the reaction to occur. As a result of this $HCl$will get completely consumed during the reaction.
For the reaction to have completely reacted with $NaOH$, $HCl$should have been present with a quantity of $5$moles. But this is not the case here

Therefore, $HCl$is the limiting reagent for the above balanced chemical reaction by $(\,5\,-\,4.5\,=\,0.5\,moles)$.

Note: Always convert the amounts of reactants to mole for solving the problems of limiting reagent. Here the amounts were already present in moles. Always balance a given chemical equation. Without balancing the equation, the actual answer may fluctuate. Always use the coefficients from a balanced reaction.