How Do You Calculate DeltaG for a Reaction at Non-Standard Pressures?

[CarbonWater]

Homework Statement

At 699 K, DeltaG (degree)=-23.25kJ for the reaction H2(g) + I2(g) <-> 2HI(g). Calculate DeltaG for this reaction if the reagents are both supplied at 10.0 atm pressure and the product is at 1.97 pressure.

Homework Equations

I believe this is the relevant equation
G=G(degree) +RT ln(P)

The Attempt at a Solution

G=-23.25kJ + 0.082 *(699+273) * ln (11.97)

but the answer is -42.1 kJ. I tried using 20, 10, and 1.97 atm and it still doesn't work. :-/

 

[danago]

Since Gibbs energy is a state property, you can try constructing a hypothetical pathway from your reactants at 10 atm to your products at 1.97 atm. You should calculate $$\Delta G$$ for each step of the pathway and then sum them.

I think the most obvious pathway looks something like this:

2 mol reactants (10 atm) ----> 2 mol reactants (1 atm)
2 mol reactants (1 atm) ----> 2 mol products (1 atm)
2 mol products (1 atm) ----> 2 mol products (1.97 atm)

So you will need to calculate $$\Delta G$$ for each of those steps.