[kimi85]

At constant pressure of 1 atm, N₂O₄ is 50% dissociated at 60 degree C, and 79% at 100 degree Celsius.  Calculate the equilibrium constantat these temperatures for the reaction N₂O₄ = 2NO₂.

This is what I did but I didn't get the right answer:

I find the delta G using the values found at the table. I multiplied each to the number of moles during the dissociation, then product minus the reactant
so, my delta G at 60C is 2365 J.  Then I used delta G = -RTlnK
I got 0.4256, but the correct answer is 1.33

For the delta H, I used delta G = delta H - T deltaS
but I my answer is still wrong.  The correct answer is 41.5 kJ.

Does anybody know what's wrong with my solution?
Thank you very much!

[Borek]

If you know how much gas is dissociated simple stoichiometry allows calculation of equilibrium concentrations, put them into reaction quotient and you are done. No need for delta G tables.

[kimi85]

Thank you sir.

I'll try it.

[Yggdrasil]

The information in the tables is usually for either 0^oC or room temperature.  You are asked to find the value at 60^oC, which will be different from the value at other temperatures.

[kimi85]

Thank you for that information.