How can you tell when a substance's free energy formation will equal 0 at T = 25 C ?

Question

kainui · Answer

Elements that are in a natural state are considered to have zero gibbs free energy. Since it's hard to know the exact amount of chemical energy in a molecule, most of thermodynamics is based on changes in values and not the values themselves. 

Check out this list, and every time you see something in the last column with a zero in it, look to the left of it and you will see only a single element type there like Al or Br2. Notice that some things can be in different allotropes. This just means they have different crystal structures. For instance, Carbon can be arranged into graphite or diamond, but diamond isn't what was decided on as being the definition. Probably because graphite is much more common and cheaper to use in a lab!

anonymous · Answer

ah, thank you so much! So would that mean Ag(s) would have 0 gibbs but not SO2 (g) since its a compound? 

Also, which list are you referring to?

kainui · Answer

http://en.wikipedia.org/wiki/List_of_standard_Gibbs_free_energies_of_formation sorry I meant to post that link in my last reply.

kainui · Answer

Yes, you are exactly right @serinaaa