Exercise on Finding the Limiting Reactant: Solutions

Nitrogen (N₂) and hydrogen (H₂) gasses react to form ammonia (NH₃) according to the following equation:
N₂ + 3H₂ → 2NH₃

Question 1: What is the limiting reactant?

Question 2: How many moles of NH₃ can be formed from 4.0 moles of N₂ and 6.0 moles of H₂?

Solution:
The first step we need to find the limiting reactant. Here is what we know for the equation:

1 mole of N₂ requires 3 moles of H₂

2 moles of N₂ require 6 moles of H₂

However, there are 4 moles of N₂ for 6 moles of H₂
Hence, N₂ is in excess and H₂ is our limiting reactant.
3 moles of H₂ make 2 moles of NH₃, 1 mole of H₂ makes 2 / 3 moles of NH₃
6 moles of H₂ = 6×(2 / 3) moles of NH₃ and so, number of moles of NH₃ = 4 moles.

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