Moles-to-moles limiting reactant

Question

Nitrogen (N2) gas and hydrogen (H2) gas react to form ammonia (NH3) gas. Suppose you have 2.0 mol of N2 and 1.0 mol of H2 in a reactor.

What would be the limiting reactant? Enter its chemical formula below.

Answer 1

Hi! To find the limiting reactant in the given reaction between nitrogen gas (N22) and hydrogen gas (H2) to produce ammonia (NH33), we need to look at the balanced chemical equation for this reaction:

N2(g)+3H2(g)→2NH3(g)

This balanced equation tells us the ratio in which we need the reactants to be present in order to form a reaction. Because Nitrogen and Hydrogen are diatomic molecules (i.e., only come in pairs!), the equation tells us that a mimimum, 1 mole of N2 reacts with 3 moles H2 to produce 2 moles of NH3. Now, based on the prompt, if we have a certain amount of starting material, let's assess which reactant will run out first:

We have 2.0 moles of N2​ & 1.0 mole of H2.

Using the ratios from the balanced equation:

The 2.0 moles of N2 would need 6.0 moles of H2 in order to be fully consumed (i.e., all the nitrogen will become ammonia). We only have 1.0 mole of H2, which is significantly than the 6.0 moles needed. Therefore, H2 (hydrogen gas) is the limiting reactant because it will run out first before all of the nitrogen gas can react. It is holding back the potential of the reaction!

Hope this helps!