Sulfur dioxide and oxygen gases react at high

Question

temperature (400 o C) in the presence of a catalyst(like Pt) to form sulfur trioxide gas. The reaction is
started from a gas mixture at 400oC with the partial pressures PSO2
= 15 atm and PO2= 10. atm. What
will be the final partial pressures of SO2(g), O2(g),and SO3(g), when the reaction is completed at400oC in a constant volume?

Answer 1

..........2SO2 + O2 ==> 2SO3
I.........15.....10.......0
You don't give a Kp; I assume the reaction is to go to completion.
SO2 can give 15 x 2 mols SO3/2 mols SO2 = 15 atm SO3.
O2 can give 10 x 2 mols SO3/1 mol O2 = 20 mols SO3; therefore,
SO2 is the limiting reagent
15 atm SO3 formed
pSO2 = 15-15 = 0
pO2 used = 15 atm SO2 x (1 mol O2/2 mol SO2) = 7.5 mols O2 used.
pO2 unused = 10-7.5 = 2.5 atm.