Question

A sample of ammonia reacts with oxygen as shown.


4NH3(g) + 5O2(g) Right arrow. 4NO(g) + 6H2O(g)


What is the limiting reactant if 4.0 g of NH3 react with 8.0 g of oxygen?
O2 because it produces only 0.20 mol of NO.
NH3 because it produces only 0.20 mol of NO.
O2 because it produces two times less NO than NH3.
NH3 because it produces three times more NO than O2.

Answer 1

O2 is the limiting reactant.

Work:
- moles NH3 = 4.0 g / 17.03 g·mol−1 ≈ 0.235 mol
- moles O2 = 8.0 g / 32.00 g·mol−1 = 0.250 mol

Reaction needs 5/4 = 1.25 mol O2 per mol NH3, so 0.235 mol NH3 would need 0.235×1.25 = 0.294 mol O2, but only 0.250 mol O2 is available → O2 limits.

Moles NO formed = 0.250 mol O2 × (4 mol NO / 5 mol O2) = 0.200 mol NO.

Thus the correct choice is: "O2 because it produces only 0.20 mol of NO."