Question

Some SO3(g), intially at 1.000 atm, is placed in an empty reaction vessel. At equilibrium, the total pressure is 1.017 atm. Assuming the partial pressures are in atmospheres, what is Kp for the reaction below?

2 SO3(g) ⇌ 2 SO2(g) + O2(g)

Answer 1

............2 SO3(g) ⇌ 2 SO2(g) + O2(g)
I...............1.................0.................0
C............-2x................2x...............x
E.............1-2x..............2x...............x

Ptotal = 1.017 = 1-2x+2x+x = 1+x so x = 0.017 atm.

Now under the E line just fill in as follows:
E.............1-2x..............2x...............x
.............1-2*0.017........2*0.017........0.017
Then plug those pressures into Kp expression and solve for Kp.
Post your work if you get stuck.
BTW, the last time I talked with Kevin s/he promised the same screen name would be used. It helps us help you if you stuck to one screen name..