CCL: Thermodynamic reversibility criterion



Gonzalo:
All elementary reactions are reversible no matter what the entropy or enthalpy changes amount to.
according  to the principle of microscopic reversibility

ie Nature does not discriminate between reactants and products ... the paths traced out from
reactant ==> product are identical to those from product ==> reactant

The connection between kinetics & thermodynamics is given by k(forward) / k(reverse) = K
where k's are rate constants and K is equilibrium constant .... from this you can relate
k(reverse) to k(forward) and Gibbs free energy or enthalpy & entropy

Trust this clarifies the position, John

At 02:58 03/03/2006, you wrote:
Sent to CCL by: "Dr. Seth Olsen" [s.olsen1**uq.edu.au]

Hi Gonzalo,

A reaction is reversible if the entropy change is zero.  If the
activation barriers are different for the forward and reverse reactions
then the forward and reverse rates will be different, but this is not
the same as thermodynamic reversibility.  I recommend Dill & Blomberg's
'Molecular Driving Forces' for further info, though most chemical
thermodynamics texts will do.

Cheers,

Seth



Gonzalo Jimenez Oses gonzalo.jimenez[#]dq.unirioja.es wrote:

>Sent to CCL by: "Gonzalo Jimenez Oses" [gonzalo.jimenez a dq.unirioja.es]
>Dear colleagues,
>
>Could anyone shed some light into the reversivility of chemical processes attending to thermodynamic criteria, please?. Everybody tend to say that a reaction is reversible when the activation barrier from the products to a TS is lower or "comparable" with the one which goes from the reactants to the same TS. My question is if there is a Gibbs energy value (or range) that could make us to discriminate between reversible and irreversible processes.
>
>Thank you all>
>
>

>


--
ccmsccmsccmsccmsccmsccmsccmsccmsccmsccmsccmsccmsccmsccmsccmsccms

Dr Seth Olsen, PhD
Postdoctoral Fellow, Biomolecular Modeling Group
Centre for Computational Molecular Science
Chemistry Building,
The University of Queensland
Qld 4072, Brisbane, Australia

tel (617) 33653732
fax (617) 33654623
email: s.olsen1{:}uq.edu.au
Web: www.ccms.uq.edu.au

ccmsccmsccmsccmsccmsccmsccmsccmsccmsccmsccmsccmsccmsccmsccmsccms



-= This is automatically added to each message by the mailing script =-
To recover the email address of the author of the message, please change
the strange characters on the top line to the % sign. You can also



      http://www.ccl.net/cgi-bin/ccl/send_ccl_message

E-mail to administrators: CHEMISTRY-REQUEST%ccl.net or use
      http://www.ccl.net/cgi-bin/ccl/send_ccl_message


      http://www.ccl.net/chemistry/sub_unsub.shtml

Before posting, check wait time at: http://www.ccl.net

Job: http://www.ccl.net/jobs
Conferences: http://server.ccl.net/chemistry/announcements/conferences/

Search Messages: http://www.ccl.net/htdig (login: ccl, Password: search)


      http://www.ccl.net/spammers.txt

RTFI: http://www.ccl.net/chemistry/aboutccl/instructions/

-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Professor John M. Simmie
Chemistry Department & Environmental Change Institute
   National University of Ireland, Galway::Ireland
     Phone: +353-91-492451::Fax: +353-91-525700
             Mobile: +353-86-805-9948
     Website: www.nuigalway.ie/chem/combust.htm