If the reaction is in gas phase u can use [A] = [A0] + RTln(p/p0) and this should give u the chemical potential ... if u have solid reagents the chemical potentials are not sensitive to the temperature, and I guess u dont have anything in solution.
Best Regards NH On Fri, Jan 16, 2009 at 10:27 PM, Roberto Veiga <roberto.ve...@ymail.com>wrote: > Ok, so I have how to know if the reaction is endothermic or not just by > calculating the four isolated systems (the two reactants and the two > products). But in order to know if the reaction is spontaneous for T>0, I > have to compute also the change in the entropy. It is not that easy, I > guess... > > Roberto > > ------------------------------ > *From:* N H <neyh...@gmail.com> > *To:* SIESTA-L@listserv.uam.es > *Sent:* Friday, January 16, 2009 10:11:41 PM > *Subject:* Re: [SIESTA-L] Hess's law > > If you have correwctly calculated all intial and finals states the answer > is yes! > > On Fri, Jan 16, 2009 at 10:02 PM, Roberto Veiga > <roberto.ve...@ymail.com>wrote: > >> Hello, >> >> if I have a substitution reaction as follows: >> >> AB+CD-->AC+BD >> >> and I calculate the four systems isolated with Siesta, can I calculate the >> enthalpy of such a reaction as stated by the Hess's law? Or there is any >> subtlety? >> >> Thanks in advance, >> >> Roberto >> >> > >
