[davidb]

Could someone tell me what I'm doing wrong? Thanks.

Question:

Estimate the value of the equilibrium constant at 645K for each of the following reactions.
2NO₂(g)  N₂O₄(g)

Attempted Solution:

[tex]\Delta G = \Delta G^0 + RT ln Q[/tex]
[tex]0 = \Delta G^0 + RT ln K[/tex]
[tex]K = \exp(- \frac{ \Delta G^0 }{RT})[/tex]

ΔG_f° NO₂(g) = 51.3 kJ/mol
ΔG_f° N₂O₄(g) = 99.8 kJ/mol

ΔG_rxn° = (1 mol * 99.8 kJ/mol) - (2 mol * 51.3 kJ/mol) = -2.8 kJ/mol

[tex]K = \exp(-\frac{-2800J}{8.314\frac{J}{mol K} 645 K}) = \exp(0.522) = 1.6856[/tex]

[curiouscat]

Why do you feel you are wrong?

[curiouscat]

Well, I'm not sure  but aren't your ΔG values for 298 K? Don't they need to be Temperature corrected to 645 K?

[davidb]

Why do you feel you are wrong?

Because masteringchemistry.com is telling me I'm wrong.  I actually have a feeling they're wrong.  Wouldn't be the first time.