Question

Ammonia reacts with oxygen to form nitric oxide and water vapor: 

4NH₃ +5O₂ → 4NO + 6H₂O 

What is the theoretical yield of water, in moles, when 40.0g NH₃ and 50.0g O₂ are mixed and allowed to react:

•  1.87 mol

•  3.53 mol

•  1.57 mol

•  1.30 mol

•  None of these

Answer 1

Number of moles of NH₃= mass/mol. wt .=40.0 g/ (17.03 g/mol)=2.348796 mol 

Number of moles of O₂= mass / mol . wt .=50.0 g /(17.03 g / mol)=1.5625 mol

According to balanced equation,

5 moles of O₂ reacts with 4 moles of NH₃

So, 1.5625 mol of O₂ would react with 1.5625 mol * 4 / 5 = 1.25 mol of NH₃

But the number of moles of NH₃ present is more than required.

That is NH₃ is the excess reagent.

O₂ is the Limiting reagent.

According to the balanced equation,

5 moles of O₂ produces 6 moles of H₂O

So, 1.5625 mol of O₂ would produce 1.5625 mol * 6 / 5=1.875 mol of H₂O

The number of moles of H₂O = 1.87 mol

Option A is the correct answer.