[jones106]

Hey guys, i'm hung up on the Gibbs Free Energy equations.  I know that ?G° is the free energy change under standard conditions (1 M, 1 atm, 25ºC), and that it is characteristic for a given reaction.  I think that when a reaction is occurring under conditions that are not standard the equation ?G=?Gº + RTlnQ is used to account for these different conditions (am I correct here?).  My problem, however, is with ?G'º (which my textbook also defines as standard free energy change.  What is the difference between ?Gº and ?G'º and when do you use which?  Does it have something to do with pH?  I just can't seem to get this.  Any help would be greatly appreciated.  Sorry for some reason my delta symbols come out as question marks.

Thank you very much,
Taylor

[Yggdrasil]

For ΔG^o, the standard conditions are 1atm, 298K, and that all reactants are at 1M.  Biologists use a ΔG^o' with a redefined set of standard conditions closer to physiological conditions.  Here the standard conditions are 1 atm, 310K (37^oC), pH 7.0, and all reactants (except hydrogen ions) at 1M.

[jones106]

Hey thanks a lot.  So I am guessing that ?Gº' is also a constant for a given reaction and would only be used when those physiological conditions are specified?  Thanks again

[Yggdrasil]

Yup.