[Big-Daddy]

How is it that the direction of change of the equilibrium constant with temperature depends on whether the reaction is exothermic or endothermic, but the derivative of ΔG° with respect to temperature contains no term for enthalpy change? ΔG°=ΔH°-TΔS°, d(ΔG°)/dT=-ΔS° ...

[mjc123]

lnK = -ΔG°/RT = -ΔH°/RT + ΔS°/R, so d(lnK)/dT = ΔH°/RT²
The two are equivalent because ΔH° and ΔS° are related to each other by ΔH° = TΔS° at the temperature at which ΔG° = 0 and K=1, so you can substitute ΔS° = (constant)*ΔH°. For equilibrium reactions, ΔH° and ΔS° are generally of the same sign - if they are of opposite sign, the equilibrium is heavily to one side or the other at all temperatures.