Question

How to find the limiting reactant in given moles?

Answer 1

Hint In single reactant reactions, the calculations can be carried out with only that amount of reactant which is converted to product. Limiting reagent concept made the calculation easy.

Complete step by step answer:
In the reactions where more than one reactant is involved, one has to first identify the limiting reactant that is the reactant which is completely consumed.
The calculations can be carried out with the amount of limiting reactant.
Now, let's know how to find the limiting reactant:
Let's assume a reaction illustrated as follows:
A + 2B $\to $ 4C
Where, A = 5 moles
 B = 8 moles
 C = 0 moles
Above mentioned quantities at its initial stage, that is why the product is 0 moles.
Number of moles of reactant by the stoichiometric coefficient equal to equivalent.
Reactant A = $\dfrac{Number\text{ }of\text{ }moles\text{ }of\text{ }reactant}{stoichiometric\text{ }coefficient}$ = $\dfrac{5}{1}$ = 5
Reactant B = $\dfrac{Number\text{ }of\text{ }moles\text{ }of\text{ }reactant}{stoichiometric\text{ }coefficient}$ = $\dfrac{8}{2}$ = 4
The reactant that produces the least number of equivalents is the limiting reactant.
So, according to our case reactant B is completely consumed at the end of the reaction that is formation of process.
Now, let's see how we can make use of reactant:
The ratio of moles by stoichiometric coefficient of limiting reactant is equal to any such equivalent of other reactant or product. With help of this we can find the number of moles of unknown product or reactant.
In our case we don't know the number of moles of product formed.
Equivalent of reactant B = Product C ,
This is equal as reactant B is the limiting reactant.
\[\dfrac{Number\text{ }of\text{ }moles\text{ }of\text{ }B}{stoichiometric\text{ }coefficient~}\] = \[\dfrac{Number\text{ }of\text{ }moles\text{ }of\text{ }C}{stoichiometric\text{ }coefficient~}\]
We don't know the number of moles of C (product).
So,
\[\dfrac{8}{2}=\dfrac{n}{4}\]
n = 16
Now, the number of moles of product C is 16.

Note: The limiting reactant that is the reactant which is completely consumed at the end of the reaction that is formation of process. The ratio of moles by stoichiometric coefficient of limiting reactant is equal to any such equivalent of other reactant or product. So, this helps us to find the unknown number of moles.