I heard that Gibbs free energy changes with temperature and pressure as
$$ \Delta G_1 = \Delta G_0 + R T \ln Q $$
But this makes no sense when pressure is zero or temperature is zero.
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asked Feb 9, 2017 at 20:22
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$\begingroup$ How so? What's the problem with T=0? $\endgroup$– Ivan NeretinCommented Feb 9, 2017 at 20:30
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3$\begingroup$ The guy's name was Gibbs, not Gibb. $\endgroup$– orthocresolCommented Feb 9, 2017 at 20:49
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1$\begingroup$ It makes no sense of either of them odd zero. Pressure can never be zero and neither do temperature. $\endgroup$– Huy NgoCommented Feb 9, 2017 at 21:41
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$\begingroup$ If the temperature is absolute zero, how is anything going to move to react? If the pressure is absolute zero, then you don't have a molecule in your volume to do any reactions. $\endgroup$– ericksonlaCommented Feb 9, 2017 at 22:48
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1 Answer
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$G^\circ = U(0K) = E^{ele}+ZPE$, i.e. the sum of the electronic energy (electrons and nuclei interacting) and the zero point vibrational energy.
You can't use $K=e^{-\Delta G^\circ/RT}$ at 0K because the derivation assumes that a certain amount of thermal energy is available. But you don't need the equation to figure out the relative amount of two molecules. At equilibrium at 0K all molecules are in the lowest possible state.
