From owner-chemistry@ccl.net Mon Jul 22 21:01:00 2013 From: "=?ISO-8859-1?Q?Jo=E3o_Brand=E3o?= jbrandao_+_ualg.pt" To: CCL Subject: CCL: Pressure Message-Id: <-48987-130722101753-28468-vVbHBel6tzNtxpHD/CYtqA .. server.ccl.net> X-Original-From: =?ISO-8859-1?Q?Jo=E3o_Brand=E3o?= Content-Type: multipart/alternative; boundary="------------020605060806070500080507" Date: Mon, 22 Jul 2013 15:17:27 +0100 MIME-Version: 1.0 Sent to CCL by: =?ISO-8859-1?Q?Jo=E3o_Brand=E3o?= [jbrandao]^[ualg.pt] This is a multi-part message in MIME format. --------------020605060806070500080507 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Hi I suppose, Bonoit is talking about reaction rate, nor chemical equilibrium. Usually, the effect of the pressure is the alteration of energy (mainly stabilization) of a reaction intermediate (complex or product) by non reactive collisions with a third partner. As this third partner is not explicit included in the rate constants, it is accounted as an effect of the total pressure. João Brandão Universidade do Algarve, Portugal Em 22-07-2013 03:03, Van Dam, Hubertus J HubertusJJ.vanDam~!~pnnl.gov escreveu: > Sent to CCL by: "Van Dam, Hubertus J" [HubertusJJ.vanDam(-)pnnl.gov] > Hi Bonoit, > > I assume you are talking about gas-phase reactions. In gas-phase reactions the pressure at which a reaction is performed shifts the equilibrium composition. If the pressure is increased the equilibrium shifts towards the side with fewer molecules and for pressure lowering the opposite happens. Differences in temperature have similar effects, with higher temperatures shifting the equilibrium to the endothermic side and vice versa. This is a straightforward application of Chatelier's principle (in the Netherlands it is referred to as the van 't Hoff principle but I haven't been able to find an obvious reference to his contribution). > > Best wishes, > > Huub van Dam > Pacific Northwest National Laboratory > Tel: 509-372-6441 > > > > > > -----Original Message----- > >> From: owner-chemistry+hubertus.vandam==pnnl.gov^^^ccl.net [mailto:owner-chemistry+hubertus.vandam==pnnl.gov^^^ccl.net] On Behalf Of bonoit bonoit bonoit_10+*+yahoo.fr >> > Sent: Sunday, July 21, 2013 11:11 AM > To: Van Dam, Hubertus J > Subject: CCL: Pressure > > > Sent to CCL by: "bonoit bonoit" [bonoit_10[-]yahoo.fr] Dear CCLers, > > I would like to enquire about the meaning of high-pressure limit and low-pressure limit and what are their influence on the rate of a given reaction. I mean why some products form in the high-pressure limit and other low-pressure limit? > What is the relation of these two pressure limits with temperature? > > Regards > Bonoithttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt> > > > --------------020605060806070500080507 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Hi

I suppose, Bonoit is talking about reaction rate, nor chemical equilibrium.

Usually, the effect of the pressure is the alteration of energy (mainly stabilization) of a reaction intermediate (complex or product) by non reactive collisions with a third partner.
As this third partner is not explicit included in the rate constants, it is accounted as an effect of the total pressure.

João Brandão
Universidade do Algarve, Portugal


Em 22-07-2013 03:03, Van Dam, Hubertus J HubertusJJ.vanDam~!~pnnl.gov escreveu: 
Sent to CCL by: "Van Dam, Hubertus J" [HubertusJJ.vanDam(-)pnnl.gov]
Hi Bonoit,

I assume you are talking about gas-phase reactions. In gas-phase reactions the pressure at which a reaction is performed shifts the equilibrium composition. If the pressure is increased the equilibrium shifts towards the side with fewer molecules and for pressure lowering the opposite happens. Differences in temperature have similar effects, with higher temperatures shifting the equilibrium to the endothermic side and vice versa. This is a straightforward application of Chatelier's principle (in the Netherlands it is referred to as the van 't Hoff principle but I haven't been able to find an obvious reference to his contribution).

Best wishes,

Huub van Dam
Pacific Northwest National Laboratory
Tel:  509-372-6441 





-----Original Message-----
  
From: owner-chemistry+hubertus.vandam==pnnl.gov^^^ccl.net [mailto:owner-chemistry+hubertus.vandam==pnnl.gov^^^ccl.net] On Behalf Of bonoit bonoit bonoit_10+*+yahoo.fr
    
Sent: Sunday, July 21, 2013 11:11 AM
To: Van Dam, Hubertus J
Subject: CCL: Pressure


Sent to CCL by: "bonoit  bonoit" [bonoit_10[-]yahoo.fr] Dear CCLers,

I would like to enquire about the meaning of high-pressure limit and low-pressure limit and what are their influence on the rate of a given reaction. I mean why some products form in the high-pressure limit and other low-pressure limit?
What is the relation of these two pressure limits with temperature?

Regards
Bonoithttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txtE-mail to subscribers: CHEMISTRY..ccl.net or use:
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