CCL: Thermodynamic reversibility criterion

[John Simmie <john.simmie[#]nuigalway.ie>]

 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