[ichidp]

For the reaction,
2SO₃ (g) :rarrow:2SO₂ (g) + O₂ (g)

ΔG= 19759 cal/mole and ΔH=46980 cal/mole.Calculate the degree of dissociation of SO₃ at 600K and 0.5 atm total pressure.

Halp please. I don't know what approach should I use, what relationship is there that I could use.. 

[SapereAude1490]

ΔG^Θ = - RTlnK^Θ

Watch the units.

Also, Kp = p_SO2 * p_O2 / p_SO3

and p_SO2 = p_total * X_SO2
       p_O2 = p_total * X_O2
       p_SO3 = p_total * X_SO3

As far as degree of dissociation is concerned, I would go about it like this

2SO₃     2SO₂ + O₂           or

 SO₃      SO₂ + 1/2O₂     

 1-α            α        1/2α

Σn = 1-α + α + 1/2α

Σn = 1 + 1/2α


so, X_SO2 = α / (1 + 1/2α)

    X_O2 = 1/2α / (1 + 1/2α)

    X_SO3 = 1-α /  (1 + 1/2α)
   
It would be nice if someone more knowledgeable can confirm it. Anyway, this will connect all the stuff you need. But I did get a cubic equation when I tried to solve it. You'll know you're on the right track if get 0<α<1 Also, I don't know what to do with the ΔH. It seems useless to me.