Question

How many mole of $Zn\left( {Fe{S_2}} \right)$ can be made from $2{\text{ }}mole$ of zinc, ${\text{3 }}mole$ of iron and ${\text{5 }}mole$ of sulphur
(A) $2{\text{ }} mole$
(B) ${\text{3 }} mole$
(C) ${\text{4 }} mole$
(D) ${\text{5 }} mole$

Answer 1

First of all we need to find the limiting reagent . Then based on the coefficient of the balanced chemical equation do the required calculation.

Complete step by step answer:
The chemical equation for the formation of $Zn\left( {Fe{S_2}} \right)$ from zinc, Iron and Sulphur is as follows :
Now from the given reaction we can see that$1{\text{ }}mole$ of zinc will reacts with $1{\text{ }}mole$ of iron and 2 mole of sulphur to form $1{\text{ }}mole$ of $Zn\left( {Fe{S_2}} \right)$. Since zinc is in lesser quantity, we will do the calculation with zinc
So , As we can see 2 mole of zinc reacts with ${\text{2 }}mole$ of iron and ${\text{4 }}mole$ of sulphur to form ${\text{2 }}mole$ of $Zn\left( {Fe{S_2}} \right)$.
Thus we say that zinc is a limiting reagent because after the reaction $1{\text{ }}mole$ of iron and ${\text{2 mole}}$ of sulphur will remain .
Hence, the correct option is (A).

Additional information: The reactant which is completely used up during an irreversible reaction is called the limiting reagent while the reactant left is called the excess reagent . In a stoichiometric equation, the coefficient of reactants and products represents their stoichiometric amounts. Stoichiometric calculations help in finding whether the production of a particular substance is economically feasible or not.

Note:
When in a problem based on chemical equation the masses of or the number of moles of all the reactants are given the reaction will stop when one of the reactants gets exhausted . In such questions sometimes apart from the amount of product produced the amount of reactant which will be left un reacted may also be asked.