Question

In the reaction `H_2S + 2O_2 -> H_2SO_4`, the law of definite proportions predicts that for every mole of `H_2S`, you will need how many moles of `O_2`?

Answer 1

Clearly it is 2 moles.

Explanation:

I would look at your equation again. You have even balanced and formatted it properly. What does it say? It says 1 molecule of hydrogen sulfide reacts with 2 molecules of oxygen to make 1 molecule of sulfuric acid.

What is the relationship between molecules and moles? A mole is simply Avogadro's number of molecules, a very large number, i.e. `N_A=6.022xx10^23` `mol^-1`. In the reaction you have given above, I could CORRECTLY say that 1 molecule of hydrogen sulfide reacts, or 1 MOLE of hydrogen sulfide reacts.

Please note that sulfuric acid is not produced in this way (from so-called conc. sour gas which sends the environmentalists screaming), and I doubt hydrogen sulfide can be oxidized up to to sulfuric acid easily.