Question

How many litres of oxygen are needed to react completely with 25.0L of H2S at STP according to the following reaction: 2H2S + 3o2 --> 2so2 + 2H2O

At STP temperature is 273 K pressure is 101.3 Kpa R is 8.314 so PV=nRT
101.3×25= n× 8.314× 273
n= 1.11 so using the molar ratio we find the moles of o2= 1.70 now how do I find the volume of O2 with only the moles and no concentration?!

Answer 1

YOu are doing it the very hard way. All the reactants are gases, same temp, pressure, so you can use the EQual Volumes law (John Dalton)

so for each 2 volumes of H2S, you need three volumes of O2
VolumesO2=3/2 * 25 liters

Answer 2

I agree with Bob Pursley that you are/were doing it the hard way; however, the answer to your question is this. After you know mols O2 = 1.70, then you know that at STP the volume of any gas is 22.4 L for one mole.
So 1.70 mols x (22.4 L/mol) = ? L.