From owner-chemistry@ccl.net Sun Apr 14 00:36:00 2019 From: "Paul.M.Mathias(a)fluor.com" To: CCL Subject: CCL: [External] CCL: Arrhenius plot and reversibility/irreversibility Message-Id: <-53680-190413231935-2866-Luvr6lu3EMKHk3gsa3mt8g ~~ server.ccl.net> X-Original-From: Paul.M.Mathias- -fluor.com Content-Type: multipart/alternative; boundary="=_alternative 00124207882583DC_=" Date: Sat, 13 Apr 2019 20:19:25 -0700 MIME-Version: 1.0 Sent to CCL by: Paul.M.Mathias{:}fluor.com This is a multipart message in MIME format. --=_alternative 00124207882583DC_= MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable My $ 0.02 as a chemical engineer: Take, A <--> B If we know the kinetics of the forward reaction rate, say R =3D k [A], we = can write the complete reaction rate, including the backward reaction, as: R =3D k [A] * {1 - [B] / [A] / K} where, K is the equilibrium constant from thermodynamics, i.e., K(T) =3D [B= ] = / [A] This simple equation ensures that the forward reaction won't go past = equilibrium for long residence times. I have used this equation to model = industrial and lab reactors. At least it meets the limiting condition. Paul Mathias > From: "Eric V. Patterson eric.patterson|-|stonybrook.edu" = To: "Mathias, Paul M. " Date: 04/13/2019 06:02 PM Subject: [External] CCL: Arrhenius plot and = reversibility/irreversibility Sent by: owner-chemistry+paul.m.mathias=3D=3Dfluor.com.:.ccl.net To add my 2=A2. One may infer something about the thermodynamics if one knows something = about the kinetics, and vice versa (see Hammond Postulate), but these are = correlations with plenty of exceptions. To truly know whether a reaction = is reversible, one must know the actual forward and reverse barriers, and = then decide what fraction of forward/reverse makes something reversible or = irreversible. Even that last step is not at all straightforward as there = are no hard cutoffs and it is subject to the molecularity issue just = mentioned by Peter. Best, Eric On Apr 13, 2019, at 12:05 PM, Peter Kraus peter.kraus : geeksonbikes.net < owner-chemistry()ccl.net> wrote: Dear Benoit, Dear Sebastian, in some cases, an "Arrhenius plot" can show the "reaction" is = irreversible: if it's not linear (on a ln(k) vs 1/T scales), and has = kinks, it's very likely not an elementary step, and microscopic = reversibility won't hold. I doubt it's possible to prove that the reaction = you have is a reversible reaction by just looking at an Arrhenius plot - = proving anything happens the way we think in kinetics is difficult! As for the plotting of "ln r", the nomenclature I was taught was based on = the rate law: r_{f,r} =3D k_{f,r} [a]^z [b]^y ... [m]^n - rate is always in = 1/s (or mol/s), rate constants (k_f or k_r) depend on the apparent = molecularity of the reaction. You can only subtract them like that, when = each side has the same molecularity! As for the "temperature and = reversibility" behaviour, I believe you're describing an equilibrium = constant, which can be calculated from thermochemistry. Best regards, Peter On Sat, 13 Apr 2019 at 17:21, Sebastian Kozuch seb.kozuch[]gmail.com < owner-chemistry-,-ccl.net> wrote: Sent to CCL by: Sebastian Kozuch [seb.kozuch(-)gmail.com] = Dear Benoit, Formally, you cannot know if a reaction is reversible or not with an = Arrhenius plot, since you are plotting the "ln k vs. 1/T", and k is just = the forward rate constant of an elementary step (i.e. it doesn't take into = consideration the possibility of the reaction going back). However, if you = graph the rate instead of the rate constant ("ln r" instead of "ln k", = with r =3D kf - kr, kf=3Dforward rare constant, kr=3Dreverse rate constant= ), = then the Arrhenius graph is completely different. I tried it in excel, considering the reactant and product concentrations = equal to one, and the forward and backward pre-exponential values (Af and = Ar) equal. This is basically "r =3D exp(-Eaf/RT) - exp (Ear/RT)". The = reverse activation energy must be larger than the forward one for an = exothermic reaction. The result is that at low temperatures the classical = Arrhenius plot (using ln kf) and this modified version (using ln r) are = equal. But at high temperatures the two diverge. While using k at high T = the graph converges to ln Af, using r the graph actually goes slowly to = minus inf. In summary, if you plot the logarithm of the rate of the elementary step = instead of the logarithm of the forward rate constant, the Arrhenius plot = will show you if the reaction is reversible if it diverges at high = temperature. The lower the temperature it diverges, the more reversible = the reaction. I don't think anybody did this analysis before. Am I right? Do we have = material for a new paper? ;) Best, Sebastian On 13/4/19 12:59 PM, Benoit Gearald ablux13:-:gmail.com wrote: Sent to CCL by: "Benoit Gearald" [ablux13++gmail.com] Dear CCLers, I would like to enquire about the relationship between the Arrhenius plot = of rate constants of a given reaction with the = reversibility/irreversibility. In other words, is it possible to know = whether the reaction is reversible or irreversible from Arrhenius plot? Regards, BenoitE-mail to subscribers: CHEMISTRY:+:ccl.net or use:E-mail to administrators: CHEMISTRY-REQUEST:+:ccl.net or use =http://www.ccl.net/chemistry= /sub_unsub.shtml=Search Messages: = http://www.ccl.net/chemistry/searchccl/index.shtmlhttp://www.ccl.net/spamme= rs.txt-- = xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx ..........Sebastian Kozuch........... xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx .Ben Gurion University of the Negev . ..........Beer Sheva, Israel......... .......... kozuch:+:bgu.ac.il ......... ....http://www.bgu.ac.il/~kozuch/.... xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx -=3D This is automatically added to each message by the mailing script = =3D-E-mail to subscribers: CHEMISTRY-,-ccl.net or use: =E-mail to administrators: = CHEMISTRY-REQUEST-,-ccl.net or use ==Before posting, check wait = time at: http://www.ccl.netConferences: = http://server.ccl.net/chemistry/announcements/conferences/ Search = Messages: http://www.ccl.net/chemistry/searchccl/index.shtmlRTFI: = http://www.ccl.net/chemistry/aboutccl/instructions/ = -- = Sent from your iPhone. No, really. ------------------------------------------------------------ The information transmitted is intended only for the person = or entity to which it is addressed and may contain = proprietary, business-confidential and/or privileged material. = If you are not the intended recipient of this message you are = hereby notified that any use, review, retransmission, dissemination, = distribution, reproduction or any action taken in reliance upon = this message is prohibited. If you received this in error, please = contact the sender and delete the material from any and all = computers and other devices. = Any views expressed in this message are those of the individual = sender and may not necessarily reflect the views of the company. = ------------------------------------------------------------ --=_alternative 00124207882583DC_= MIME-Version: 1.0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable My $ 0.02 as a chemi= cal engineer:

Take, A <--&g= t; B

If we know the kinetics of the forward reaction rate, say R =3D k [A], we can write the complete reaction rate, including the backward reaction, as:

R =3D k [A] * {1 - [B] / [A] / K}

where, K is the equilibrium constant from thermodynamics, i.e., K(T) =3D [B] / [A]

This simple equa= tion ensures that the forward reaction won't go past equilibrium for long reside= nce times.  I have used this equation to model industrial and lab reactors.  At least it meets the limiting condition.

Paul Mathias



Fro= m:        "Eric V. Patterson eric.patterson|-|stonybrook.edu" <owner-chemistry.:.ccl.= net>
To:        "Mathias, Paul M. " <paul.m.mathias.:.fluor.com>
Dat= e:        04/13/2019 06:02 PM
Sub= ject:        [External] CCL: Arrhenius plot and reversibility/irreversibility
Sent by:        owner-chemistry+paul.m.mathias=3D=3Dfluor.com.:.ccl.net



To add my 2=A2.

One may infer something about the thermodynamics if one knows something about the kinetics, and vice versa (see Hammond Postulate), but these are correlations with plenty of exceptions.  To truly know whether a reaction is reversible, one must know the actual forward and reverse barriers, and then decide what fraction of forward/reverse makes something reversible or irreversible.  Even that last step is not at all straightforward as there are no hard cutoffs and it is subject to the molecularity issue just mentioned by Peter.

Best,
Eric



On Apr 13, 2019, at 12:05 PM, Peter Kra= us peter.kraus : geeksonbikes.net <owner-chemistry()ccl.net> wrote:

Dear Benoit, Dear Sebastian,

in some cases, an "Arrhenius plot&= quot; can show the "reaction" is irreversible: if it's not linear (on a ln(k) vs 1/T scales), and has kinks, it's very likely not an elementary step, and microscopic reversibility won't hold. I doubt it's possible to prove that the reaction you have is a reversible reaction by just looking at an Arrhenius plot - proving anything happens the way we think in kinetics is difficult!

As for the plotting of "ln r", the nomenclature I was taught was based on the rate law: r_{f,r} =3D k_{f,r} [a]^z [b]^y ... [m]^n - rate is always in 1/s (or mol/s), rate constants (k_f or k_r) depend on the apparent molecularity of the reaction. You can only subtract them like that, when each side has the same molecularity! As for the "temperature and reversibility" behaviour, I believe you're describing an equilibrium constant, which can be calculated from thermochemistry.

Best regards,
Peter


On Sat, 13 Apr 2019 at 17:21, Sebastian Kozuch seb.kozuch[]gmail.com <owner-chemistry-,-ccl.net> wrote:

Sent to CCL by: Sebastian Kozuch [seb.kozuch(-)gmail.com]


Dear Benoit,
Formally, you cannot know if a reaction is reversible or not with an Arrhen= ius plot, since you are plotting the "ln k vs. 1/T", and k is just the forward rate constant of an elementary step (i.e. it doesn't take into consideration the possibility of the reaction going back). However, if you graph the rate instead of the rate constant ("ln r" instead of "ln k", with r =3D kf - kr,  kf=3Dforward rare constant, kr=3Dreverse rate constant), then the Arrhenius graph is completely differe= nt.
I tried it in excel, considering the reactant and product concentrations equal to one, and the forward and backward pre-exponential values (Af and Ar) equal. This is basically "r =3D exp(-Eaf/RT) - exp (Ear/RT)". The reverse activation energy must be larger than the forward one for an exothermic reaction. The result is that at low temperatures the classical Arrhenius plot (using ln kf) and this modified version (using ln r) are equal. But at high temperatures the two diverge. While using k at high T the graph converges to ln Af, using r the graph actually goes slowly to minus inf.
In summary, if you plot the logarithm of the rate of the elementary step instead of the logarithm of the forward rate constant, the Arrhenius plot will show you if the reaction is reversible if it diverges at high temperat= ure. The lower the temperature it diverges, the more reversible the reaction.
I don't think anybody did this analysis before. Am I right? Do we have material for a new paper? ;)

Best,
Sebastian
On 13/4/19 12:59 PM, Benoit Gearald abl= ux13:-:gmail.com wrote:
Sent to CCL by: "Benoit  = Gearald" [ablux13++gmail.com<= span style=3D" font-size:12pt">]
Dear CCLers,

I would like to enquire about the relationship between the Arrhenius plot
of rate constants of a given reaction with the
reversibility/irreversibility. In other words, is it possible to know
whether the reaction is reversible or irreversible from Arrhenius plot?

Regards,

BenoitE-mail to subscribers: CHEM= ISTRY:+: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

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--
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
..........Sebastian Kozuch...........
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.Ben Gurion University of the Negev .
..........Beer Sheva, Israel.........
.......... kozuch:+:bgu.ac.il<= /span> .........
....http://www.bgu.ac.il/~kozuch/..<= /span>..
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--------------------------------------= ---------------------- --=_alternative 00124207882583DC_=-- From owner-chemistry@ccl.net Sun Apr 14 07:30:00 2019 From: "Benoit Gearald ablux13-*-gmail.com" To: CCL Subject: CCL: Transition state Message-Id: <-53681-190414072916-22384-tcVvgveEkyQWMrPBBYS+vQ#server.ccl.net> X-Original-From: "Benoit Gearald" Date: Sun, 14 Apr 2019 07:29:14 -0400 Sent to CCL by: "Benoit Gearald" [ablux13---gmail.com] Dear CCLers, Is it possible to locate a transition state for the formation of three- membered cycle like an epoxyde? Best regards, Benoit From owner-chemistry@ccl.net Sun Apr 14 09:27:00 2019 From: "Eric V. Patterson eric.patterson(~)stonybrook.edu" To: CCL Subject: CCL: Transition state Message-Id: <-53682-190414092601-28571-a/dl9aMAUkhXzQ/peQktiw##server.ccl.net> X-Original-From: "Eric V. Patterson" Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=us-ascii Date: Sun, 14 Apr 2019 09:25:54 -0400 Mime-Version: 1.0 (Mac OS X Mail 12.4 \(3445.104.8\)) Sent to CCL by: "Eric V. Patterson" [eric.patterson|*|stonybrook.edu] Dear Benoit, Yes, most definitely. I have done so many times. Now, it would be helpful to know whether you are trying to model epoxidation via some process like ozonolysis of an alkene, or whether you are forming the epoxide from something like a halohydrin. The latter is straightforward, the former less so. Best, Eric > On Apr 14, 2019, at 7:29 AM, Benoit Gearald ablux13-*-gmail.com wrote: > > > Sent to CCL by: "Benoit Gearald" [ablux13---gmail.com] > Dear CCLers, > > Is it possible to locate a transition state for the formation of three- > membered cycle like an epoxyde? > > Best regards, > > Benoit> > From owner-chemistry@ccl.net Sun Apr 14 10:14:01 2019 From: "Eric V. Patterson eric.patterson||stonybrook.edu" To: CCL Subject: CCL: Transition state Message-Id: <-53683-190414101246-16459-f7WBaqZVmoUfBgrx3V2Zkw!=!server.ccl.net> X-Original-From: "Eric V. Patterson" Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=us-ascii Date: Sun, 14 Apr 2019 10:12:39 -0400 Mime-Version: 1.0 (Mac OS X Mail 12.4 \(3445.104.8\)) Sent to CCL by: "Eric V. Patterson" [eric.patterson_-_stonybrook.edu] Correction: I did not mean ozonolysis. I meant mCPBA. > On Apr 14, 2019, at 9:25 AM, Eric V. Patterson eric.patterson(~)stonybrook.edu wrote: > > > Sent to CCL by: "Eric V. Patterson" [eric.patterson|*|stonybrook.edu] > Dear Benoit, > > Yes, most definitely. I have done so many times. Now, it would be helpful to know whether you are trying to model epoxidation via some process like ozonolysis of an alkene, or whether you are forming the epoxide from something like a halohydrin. The latter is straightforward, the former less so. > > Best, > Eric > > >> On Apr 14, 2019, at 7:29 AM, Benoit Gearald ablux13-*-gmail.com wrote: >> >> >> Sent to CCL by: "Benoit Gearald" [ablux13---gmail.com] >> Dear CCLers, >> >> Is it possible to locate a transition state for the formation of three- >> membered cycle like an epoxyde? >> >> Best regards, >> >> Benoit> > From owner-chemistry@ccl.net Sun Apr 14 13:15:01 2019 From: "bonoit bonoit ablux13^^^gmail.com" To: CCL Subject: CCL: Transition state Message-Id: <-53684-190414131335-13261-o++VWANh7RaoEs0wAwFCWQ^server.ccl.net> X-Original-From: bonoit bonoit Content-Type: text/plain; charset="UTF-8" Date: Sun, 14 Apr 2019 19:13:29 +0200 MIME-Version: 1.0 Sent to CCL by: bonoit bonoit [ablux13[*]gmail.com] Dear Eric, Thank you for your response. In fact, I have found a transition state with a very very low barrier (under reactants) and I 've checked it with IRC and it really connects with the corresponding minima of reactants and epoxyde product. Regards Benoit 2019-04-14 16:12 UTC+02:00, Eric V. Patterson eric.patterson||stonybrook.edu : > > Sent to CCL by: "Eric V. Patterson" [eric.patterson_-_stonybrook.edu] > Correction: I did not mean ozonolysis. I meant mCPBA. > >> On Apr 14, 2019, at 9:25 AM, Eric V. Patterson >> eric.patterson(~)stonybrook.edu wrote: >> >> >> Sent to CCL by: "Eric V. Patterson" [eric.patterson|*|stonybrook.edu] >> Dear Benoit, >> >> Yes, most definitely. I have done so many times. Now, it would be >> helpful to know whether you are trying to model epoxidation via some >> process like ozonolysis of an alkene, or whether you are forming the >> epoxide from something like a halohydrin. The latter is straightforward, >> the former less so. >> >> Best, >> Eric >> >> >>> On Apr 14, 2019, at 7:29 AM, Benoit Gearald ablux13-*-gmail.com >>> wrote: >>> >>> >>> Sent to CCL by: "Benoit Gearald" [ablux13---gmail.com] >>> Dear CCLers, >>> >>> Is it possible to locate a transition state for the formation of three- >>> membered cycle like an epoxyde? >>> >>> Best regards, >>> >>> Benoit> > > From owner-chemistry@ccl.net Sun Apr 14 13:49:00 2019 From: "=?UTF-8?B?RW1pbGlvIEouIEp1w6FyZXogUMOpcmV6?= ejjuarezperez##gmail.com" To: CCL Subject: CCL: Arrhenius plot and reversibility/irreversibility Message-Id: <-53685-190414110324-13488-d+th5o/jAja0YScWUMAfzw]=[server.ccl.net> X-Original-From: =?UTF-8?B?RW1pbGlvIEouIEp1w6FyZXogUMOpcmV6?= Content-Language: es-ES Content-Transfer-Encoding: 8bit Content-Type: text/html; charset=utf-8 Date: Mon, 15 Apr 2019 00:03:13 +0900 MIME-Version: 1.0 Sent to CCL by: =?UTF-8?B?RW1pbGlvIEouIEp1w6FyZXogUMOpcmV6?= [ejjuarezperez.:.gmail.com]
Metadynamics could help you to elucidate the reversibility/irreversibility of the reaction. Stationary DFT thermo-chemistry shows the initial and final state for the reaction and the energy pathway connecting such states could be obtained from metadynamics including activation energy barriers, or valley/sinks of stability etc. The shape of the curve (or (meta-)surface, it depends of the number of collective variables chosen describing the reaction) could give you clues about the reversibility of the reaction.




I applied it recently and obtained satisfactory results for what I was looking for. Sorry for the s p a m (it is an open article too)

https://pubs.acs.org/doi/10.1021/acsami.9b02374

Also, I made a gif about it only for fun

https://twitter.com/ejjuarezperez/status/1108283285560393735




El 13/4/19 a las 18:59, Benoit Gearald ablux13:-:gmail.com escribió:
Sent to CCL by: "Benoit  Gearald" [ablux13++gmail.com]
Dear CCLers,

I would like to enquire about the relationship between the Arrhenius plot 
of rate constants of a given reaction with the 
reversibility/irreversibility. In other words, is it possible to know 
whether the reaction is reversible or irreversible from Arrhenius plot?

Regards,

BenoitE-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

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From owner-chemistry@ccl.net Sun Apr 14 15:55:00 2019 From: "Eric V. Patterson eric.patterson%x%stonybrook.edu" To: CCL Subject: CCL: Transition state Message-Id: <-53686-190414155357-19248-C8g0CzEvj1la+nnHCuT/uQ::server.ccl.net> X-Original-From: "Eric V. Patterson" Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=us-ascii Date: Sun, 14 Apr 2019 15:53:50 -0400 Mime-Version: 1.0 (Mac OS X Mail 12.4 \(3445.104.8\)) Sent to CCL by: "Eric V. Patterson" [eric.patterson/a\stonybrook.edu] Benoit, Is the negative barrier measured as deltaE(SCF), deltaH or deltaG? An IRC is an E(SCF) thing, so there might be an explanation there. It is definitely possible for thermodynamic corrections to switch the relative ordering of stationary points that have very similar electronic energies. If the IRC goes downhill in both directions and connects to the correct minima, then the stationary points would appear to be correct. Cheers, Eric > On Apr 14, 2019, at 1:13 PM, bonoit bonoit ablux13^^^gmail.com wrote: > > > Sent to CCL by: bonoit bonoit [ablux13[*]gmail.com] > Dear Eric, > > Thank you for your response. In fact, I have found a transition state > with a very very low barrier (under reactants) and I 've checked it > with IRC and it really connects with the corresponding minima of > reactants and epoxyde product. > > Regards > > Benoit > > 2019-04-14 16:12 UTC+02:00, Eric V. Patterson > eric.patterson||stonybrook.edu : >> >> Sent to CCL by: "Eric V. Patterson" [eric.patterson_-_stonybrook.edu] >> Correction: I did not mean ozonolysis. I meant mCPBA. >> >>> On Apr 14, 2019, at 9:25 AM, Eric V. Patterson >>> eric.patterson(~)stonybrook.edu wrote: >>> >>> >>> Sent to CCL by: "Eric V. Patterson" [eric.patterson|*|stonybrook.edu] >>> Dear Benoit, >>> >>> Yes, most definitely. I have done so many times. Now, it would be >>> helpful to know whether you are trying to model epoxidation via some >>> process like ozonolysis of an alkene, or whether you are forming the >>> epoxide from something like a halohydrin. The latter is straightforward, >>> the former less so. >>> >>> Best, >>> Eric >>> >>> >>>> On Apr 14, 2019, at 7:29 AM, Benoit Gearald ablux13-*-gmail.com >>>> wrote: >>>> >>>> >>>> Sent to CCL by: "Benoit Gearald" [ablux13---gmail.com] >>>> Dear CCLers, >>>> >>>> Is it possible to locate a transition state for the formation of three- >>>> membered cycle like an epoxyde? >>>> >>>> Best regards, >>>> >>>> Benoit> >