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

Hint: 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.