Identify the limiting reagent when 14g N2 combines with 2g H2 to form NH3

Question

Identify the limiting reagent when 14g N2 combines with 2g H2 to form NH3

Answer 1

Hello Rose

 

We first need to write the balanced chemical reaction.

 

N₂ + 3H₂ → 2NH₃

 

By definition, the limiting reagent will be the substance that will be completely consumed in the reaction.  The method I like to use to figure out the limiting reagent is to start with the mass of each reactant and convert them to the # of moles of the product.  The reactant that produces the least amount of product will be the limiting reagent.

 

The process for this can be written as:

 

g N₂ → mol N₂ → mol NH₃

g H₂ → mol H₂ → mol NH₃

 

The mole ratio from the balanced chemical reaction between N₂ and NH₃ is 1:2, and between H₂ and NH₃ is 3:2.  Molar mass of N₂ = 28 g/mol, and H₂ = 2 g/mol.

 

14 g N₂ x (1 mol N₂ / 28 g N₂) x (2 mol NH₃  / 1 mol N₂) = 1 mol NH₃

 

2 g H₂ x (1 mol H₂ / 2 g H₂) x (2 mol NH₃ / 3 mol H₂) = 0.7 mol NH₃

 

As you can see, H₂ produces less NH₃, therefore, it is the limiting reagent.