please tell me how to find a limiting reagent with the help of a example

 

Limiting reagent: 

Many a time, the reactions are carried out when the reactants are not present in the amounts as required by a balance chemical reaction. In such situations, one reactant is in excess over the other. The reactant whicj is present in the lesser amounts gets consumed after sometime and after that no further reaction takes place whatever be the amount of the other reactant present. Hence, the reactant which gets consumed, limits the amount of product formed and is, therefore called the limiting reagent.

 

For example: 

 

N₂ + 3H₂ → 2NH₃.

Molecular mass of Nitrogen = 28 g/mol = 0.028 kg/mol

Molecular mass of Hydrogen = 6 g/mol = 0.006 kg/mol

Molecular mass of Ammonia = 17 g/mol = 0.017 kg/mol

Now, according to the balanced chemical equation, 0.028 kg of Nitrogen reacts with 0.006 kg of Hydrogen.

So, 50 kg of Nitrogen reacts with (0.006 x 50) / 0.028  = 10.71 kg of Hydrogen.

The amount of Hydrogen given (10 kg) is less than the amount required (10.71 kg) for 50 kg of Nitrogen.

Therefore, Hydrogen is the limiting reagent. the formation of Ammonia will depend on the amount of Hydrogen  available for reaction.

0.006 kg of Nitrogen produces (2x0.017) = 0.034 kg of Ammonia.

So, 10 kg of Hydrogen will produce (0.034 x 10) / 0.006 = 56.67 kg of Ammonia.