[Big-Daddy]

If we have two equilibrium constants [itex]K_1[/itex] and [itex]K_2[/itex], measured at [itex]T_1[/itex] and [itex]T_2[/itex] respectively, for a certain reaction, should there not be a ΔG° relationship between them? If ΔG°=-R*T*ln(K) then it follows that ln(K₂/K₁)=-(ΔG°/R)*(1/T₂-1/T₁) as far as I can see (just divide K₂ by K₁). But then if you try replacing with ΔG°=ΔH°-T·ΔS°, ΔS° falls out and we end up with ln(K₂/K₁)=-(ΔH°/R)*(1/T₂-1/T₁). How can both formulae be correct - doesn't that suggest ΔG°=ΔH°, which is not necessarily (almost never) true?

[curiouscat]

If we have two equilibrium constants [itex]K_1[/itex] and [itex]K_2[/itex], measured at [itex]T_1[/itex] and [itex]T_2[/itex] respectively, for a certain reaction, should there not be a ΔG° relationship between them? If ΔG°=-R*T*ln(K) then it follows that ln(K₂/K₁)=-(ΔG°/R)*(1/T₂-1/T₁) as far as I can see (just divide K₂ by K₁). But then if you try replacing with ΔG°=ΔH°-T·ΔS°, ΔS° falls out and we end up with ln(K₂/K₁)=-(ΔH°/R)*(1/T₂-1/T₁). How can both formulae be correct - doesn't that suggest ΔG°=ΔH°, which is not necessarily (almost never) true?

You are assuming ΔG° is invariant with Temperature? That'd be a HUGE bug in your derivation right there (I think).

This itself is wrong: ln(K2/K1)=-(ΔG°/R)*(1/T2-1/T1)

[Big-Daddy]

Sorry, big mistake by me. Yeah, I see where I went wrong now. Thanks