A Question About Stoichiometry

Question

Hi,

We just started Stoichiometry. I answered the question below, but the website (Sapling) tells me it's wrong.

"If 3 molecules of N₂ react with 6 molecules of H₂ , determine the number of molecules of NH₃ that could form from each starting material."

" (3 molecules of N₂) * [ (X molecules of X) divided by (X molecules of X) ] = X molecules of NH₃ "

" (6 molecules of H₂) * [ (X molecules of X) divided by (X molecules of X) ] = X molecules of NH₃ "

It then asks what the limiting reactant is.

Answer 1

Hello, Jackson,

.

We need a balanced equation for this:

3N₂ + 6H₂ = ?NH₃

We have 6 N and 12 H coming in. But NH₃ requires 3 H per 1 N, so there is a imbalance. 6 N coming in can produce 6 NH₃, but that would require 18 H's, and we only have 12 coming in. That means hydrogen is the limiting reagent. The most you can make is 4NH₃, if we have the numbers of molecules mentioned.

The sentences with X's are a confusing to me. If we have 3 N coming in, we could make 3 NH₃ molecules, and so forth. I hope you can use this approach to answer the questions, assuming you understand what is being requested (I can't).

Bob

Answer 2

The balanced reaction is N₂ + 3 H₂ -> 2 NH₃

Therefore 3 mol of N₂ gives 6 mol NH₃ (3 mol N₂) * (2 mol NH₃/ 1 mol N₂)

And 6 mol H₂ gives 4 mol NH₃ (6 mol H₂) * (2 mol NH₃/ 3 mol H₂)

Knowing this you can find the limiting reagent.