Understanding the "Relationship between number of molecules"

Question

In the Ostwald Process, 4 molecules of ammonia and 5 molecules of oxygen react to produce 4 molecules of nitric oxide and 6 molecules of water.  Which of the following equations correctly models the relationship between the number of molecules of nitric oxide, n, and the number of molecules of water, w, produced by the reaction? 

 

I would think that it would come down to 2n=3w, but the correct answer is 3n=2w.  Can anyone help me understand why it would be this and not my guess?

Answer 1

You seem to be correct.  The mole ratio is 4 moles (or molecules) of NO to 6 moles (or molecules) of H2O.  This reduces to a ratio of 2 : 3 or 2n = 3w.  

 

The only thing I could say about this is that either the answer key is incorrect, or they are asking something else. This is NOT the entire Ostwald Process.  The Ostwald Process is a means of preparing nitric acid, HNO3.  Once the nitric acid is formed in the reaction you mention, then...

2NO + O2 ==> 2NO2  and further reaction gives

3NO2 + H2O ==> 2HNO3

 

So, the ratio of NO to HNO3 is 3:2 but that doesn't seem to be what the original question is asking.