Question

Initially a vessel is charged at 1000K with SO3 at a partial pressure of 0.5atm. At equilibrium the SO3 partial pressure is 0.2atm. Calculate the value of Kp at 1000K. 2SO3->2SO2+O2

My answer:
0.5-0.2=0.3atm
SO2=0.3atm*2/2mol= 0.3
O2=0.3atm*1/2mol=0.8
Therefore 0.8-0.3=0.5

Tbook answer: 0.338

Answer 1

You should have set up an ICE chart.
.........2SO3 ==> 2SO2 + O2
I.........0.5.....0.......0
C.........-2x.....2x......x
E......0.5-2x.....2x.......x

The problem tells you that 0.5-2x = 0.2
Solve for x and evaluate SO2 and O2, substitute into Keq and solve for K.
I get 0.3375 which rounds to 0.338.