The = high- and low-pressure limits relate to the different behaviour of a = unimolecular reaction; specifically to the rate of reaction at these = extremes at a constant temperature. At infinitely high-pressure = the reaction is first order in reactant and at low pressures the = reaction becomes second order … first order in reactant and first = order in the bath gas. It becomes more difficult to observe the = hi-pressure limit experimentally at high temperatures and with small = molecules.

Most university level = physical chemistry texts describe this situation and those are better = places to start your enquiries.

J. M. = Simmie//NUIG//Ireland

>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

>Bonoit

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-----

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: 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_messagehttp://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/chemistry/searchccl/index.shtmlhttp://www.ccl.net/spammers.txt RTFI: http://www.ccl.net/chemistry/aboutccl/instructions/

Sent to CCL by: "bonoit bonoit" [bonoit_10[a]yahoo.fr] Dear CCLers, I would like to enquire about the oxygen atom. What is the difference between the O(3P) and O(1D)? Regards BonoitE-mail to subscribers: CHEMISTRY!A!ccl.net or use: http://www.ccl.net/cgi-bin/ccl/send_ccl_message E-mail to administrators: CHEMISTRY-REQUEST!A!ccl.net or use http://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://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/chemistry/searchccl/index.shtmlhttp://www.ccl.net/spammers.txt RTFI: http://www.ccl.net/chemistry/aboutccl/instructions/