After the reaction has gone to completion, which gas remains in excess and how much is present?

Ammonia reacts with oxygen to form gaseous nitirc oxide and steam. Initially 2 moles of ammonia is mixed with 1 mole of oxygen.

Could you please show working

Answer:
4NH3+5O2-->4NO+ 6H2O

at completion, the ammonia will remain because 1.25 moles of O2 reacts with one mole of NH3

1mole O2 (4moles NH3/5 mole O2) = .8 moles NH3 needed to react to completion

so 1.2 moles NH3 left
2NH3 + 3O2 >> N2O3 + 3H2O
The ratio between NH3 and O2 is 2 : 3 so O2 is the limiting reactant
2 : 3 = x : 1
x = 2/3 = 0.667 moles NH3 needed for the reaction
2 - 0.667 = 1.33 moles NH3 in excess
4NH3 + 5O2 ==> 4NO + 6H2O

=> 5 mols of O2 reacts with 4 mols of NH3
=> 1 mol NH3 reacts with 4/5 = 0.8 mol of NH3

but NH3 was taken 2 mols
=> NH3 will be leftover & 2 - 0.8 = 1.2 mols of NH3 will remain unreacted.
Commercially, NO is produced by the oxidation of ammonia at 750 to 900 °C (normally at 850 °C) in the presence of platinum as catalyst:

4NH3 + 5O2 → 4NO + 6H2O

from the above equation 5 moles of oxygen react with 4 moles of ammonia to produce 4 moles of nitric oxide. but, here limiting concentration is oxygen, as only 1 mole of oxygen is available , so it will react with 4/5 moles of ammonia to produce 4/5 moles of nitric oxide.
The remaining gas will be ammonia =2-4/5 = 1.2 moles.

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