[madscientist]

hi everyone,

Just wondering if this is how you write the expression for the equilibrium constant for the following reaction:

SO_2(g) + 1/2 O_2(g) <=====> SO_3(l)

my working is:

K = [a _SO3 ] / [a _SO2 ][a _O2 ] ^1/2

I also need to calculate the value of "K" from dG_rxn = -70890.0 J/mol

so:

                            -RT lnK = dG_rxn

    -(8.314 J/K.mol)(298K) lnK = -70890.0 J

                                  lnK = -70890.0 J / -(8.314 J/K.mol)(298K)

                                  lnK = 28.612690166

                                    K = e^28.612690166

                                       = 2.6689*10¹²

another part to this question is:

If 1.00 bar of SO2 and 1.00 bar of O2 are enclosed in a system in the presence of some SO3 liquid, in which direction would the equilibrium move?

Now all I could think of is that they dont want a numerical answer and that because the value for the equilibrium constant K is extremely large, this indicates that there is alot more products than reactants at equilibrium (doesnt it), especially when if you look at that equation the product (SO3) is in its liquid state and its activity is approx = 1

therefore:  K = 1 /  [a _SO2 ][a _O2 ] ^1/2

this says that at equilibrium, there is 2.6689*10¹² times more SO₃ than the multiplication of [a _SO2 ][a _O2 ] ^1/2.

can anyone tell me if my reasoning is correct?

cheers,

madscientist  :drunk:

[Mitch]

What is the "a"in your K constant equation. Isn't [] used for concentrations, how can you have a concentration for a gas?

[Borek]

how can you have a concentration for a gas?

Oxygen concentration in air is about 20%