Question

Define the following term Limiting reagent.

Answer 1

Limiting Reagent:

The reactant which gets completely consumed the course of the reaction is called limiting reagent.

For eg.

The balanced chemical equation is given as;

$1PbS+4H_2{O}_2\to 1{PbSO}_4+4H_{2}O$

Initial moles$\to$$5$mol $18$moles

and we have to calculate the maximum amount of ${PbSO}_4$ being produced.

$1$mol of PbS reacts with $4$mol of $H_2{O}_2$ to give $1$ mole of ${PbSO}_4$.

So $5$mol of PbS will react with $20$moles of $H_2{O}_2$

But moles of $H_2{O}_2$ is only $18$

So $H_2{O}_2$ is the reagent which is consumed first and hence it is the limiting reagent,

$4molof{H}_2{O}_2\to 1molof{PbSO}_{4}1molof{H}_2{O}_2\to \frac{1}{4}molof{PbSO}_{4}18molof{H}_2{O}_2\to \frac{18}{4}molof{PbSO}_4-4.5molof{PbSO}_4$

If $PbS$ was the limiting reagent, $5$mol of PbS would give $5$mol of ${PbSO}_4$ but it is not so.