An important reaction sequence in the industrial production of nitric acid is the following:


starting from 20.0 mol of nitrogen gas in the first reaction, how many moles of oxygen gas are required in the second one?
a) 12.5 mol o₂
b) 20.0 mol o₂
c) 25.0 mol o₂
d) 50.0 mol o₂
e) 100. mol o₂

25.0 mol O₂ are required in the second reaction

Explanation:

N₂ (g) + 3H₂ (g)  →  2NH₃ (g)

4NH₃ (g)  +  5O₂ (g)  →  4NO (g) + 6 H₂O(l)

Molar ratio in first reaction is 1:2

For every mol of N₂. I make 2 moles of ammonia. If I have 20 moles of N₂, i'm going to get, 40 moles of ammonia.

In the second reaction, molar ratio between products is 4:5.

If I obtained 40 moles of ammonia in first step, let's prepare the rule of three.

4 moles of ammonia react with 5 moles of O₂

40 moles of ammonia react with ( 40.5) /4 = 25moles