Solution:
Balanced chemical equation:
N2 + 2O2 → 2NO2
According to the equation above: 2×n(N2) = n(O2) = n(NO2)
Moles of each reactant:
n(N2) = 5 mol
n(O2) = 12 mol
Choose one reactant and determine how many moles of the other reactant are necessary to completely react with it. Let's choose N2:
n(O2) = 2 × n(N2) = 2 × 5 mol = 10 mol
The calculation above means that we need 10 mol of O2 to completely react with N2.
We have 12 mol of O2 and therefore more than enough oxygen gas.
Thus oxygen gas (O2) is in excess and nitrogen gas (N2) must be the limiting reagent.
Therefore,
n(NO2) = 2 × n(N2) = 2 × 5 mol = 10 mol
Moles of NO2 = 10 mol
Answer: 10 mol of NO2 are produced.