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Verandering in sintesetempo van 'n molekule verander ewewigskonsentrasie

Verandering in sintesetempo van 'n molekule verander ewewigskonsentrasie


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Ek het die onderwerp gelees van 'Die konsentrasie van die molekule kan net vinnig aangepas word as die leeftyd van 'n molekule kort is' vanaf Molekulêre Biologie van die Sel deur Alberts.

Aan die einde van bl-837 (hierdie deel kan ook hier gevind word), sê die skrywer -

"Trouens, nadat 'n molekule se sintesetempo óf verhoog óf skielik verminder is, is die tyd wat nodig is vir die molekule om halfpad van sy ou na sy nuwe ewewigskonsentrasie te verskuif gelyk aan sy normale halfleeftyd - dit wil sê gelyk aan die tyd dit sou nodig wees om die konsentrasie daarvan met die helfte te daal as alle sintese gestop word."

Wat bedoel hulle presies met 'verskuif halfpad'? Ek is nie in staat om heeltemal duidelik te verstaan ​​wat die bogenoemde sin beteken nie. Ek hoop van julle kan my dalk help. Dankie.


Let wel: Die term ewewig is anders as bestendige toestand w.t.t. chemiese reaksies. Bestendige toestand is die regte term vir bogenoemde voorbeeld. Ekwilibrium word gebruik in die sin van voorwaartse en terugwaartse reaksies in 'n enkele omkeerbare reaksie. Die voorbeeld hierbo beskou twee onomkeerbare reaksies - produksie en afbraak.

… die tyd wat nodig is vir die molekule om halfpad van sy ou na sy nuwe ewewigskonsentrasie te skuif is gelyk aan sy normale halfleeftyd

Dit is nie waar as die afbraakreaksie nulde orde is of as hierdie reaksies nie-lineêr is nie. Maar vir 'n lineêre produksie-degradasie-reeks reaksies ($X$ is 'n biomolekule wat teen 'n konstante tempo $alpha$ gevorm word en teen 'n eerste-orde tempo $eta$ afgebreek word), kan die reaksietempo deur die volgende vergelyking voorgestel word.

$$frac{d[X]}{dt}igg|_1=alpha _1 - eta [X]$$

By bestendige toestand $frac{d[X]}{dt}=0$, wat beteken $[X_{ss_1}]=Grootfrac{alpha _1}{eta}$

Halfleeftyd soos gedefinieer, deur $alpha$=0 te stel en die differensiaalvergelyking op te los = ${Large frac{log(2)}{eta}}$

Wanneer die formasietempo na 'n nuwe waarde verander word:

$$frac{d[X]}{dt}igg|_2=alpha _2 - eta [X]$$

en $[X_{ss_2}]=Largefrac{alpha _2}{eta}$

Uit die bogenoemde vergelyking kan die volgende vergelyking afgelei word (deur die differensiaalvergelyking te integreer):

$$-frac{1}{eta}.log(alpha _2 - eta [X]){groot|}_{X_{aanvanklike}} ^{X_{finale}}= t_{frac{ 1}{2}} $$

wanneer jy $X_{initial}=X_{ss_1}=frac{alpha _1}{eta}$ en $X_{final}=Largefrac{frac{alpha _2}{eta} vervang - frac{alpha _1}{eta}}{2}$ (halfpad tussen nuwe bestendige toestand en ou bestendige toestand)

jy sal kry: $$t_{frac{1}{2}}= -frac{1}{eta}logleft(frac{alpha _2 -etafrac{alpha _1}{ beta}}{alpha _2 - eta frac{frac{alpha _2}{eta} - frac{alpha _1}{eta}}{2}} ight) = frac{log( 2)}{eta} $$


Dinamiese ewewig en le Chatelier se beginsel

Omkeerbare reaksies: 'n Reaksie wat plaasvind in beide vorentoe en
keer rigtings om indien omkeerbaar. Ewewig slegs in omkeerbaar
reaksies.
• Dinamiese ewewigstelsel: Ewewig wat in 'n geslote sisteem bestaan ​​wanneer die tempo van vorentoe beweeg
reaksie is gelyk aan tempo van terugwaartse reaksie is dinamiese ewewig. Konsentrasies van reaktante
en produkte verander nie. Beide reaksies vind plaas, dit is watter kant ook al oorheers. Waar
pH sal konstant bly.
• Hoe Dinamiese Ekwilibrium bereik: Tempo van voorwaartse reaksie vertraag en tempo van agteruit
reaksie versnel totdat die tempo van voorwaartse reaksie dieselfde is as die tempo van die terugwaartse reaksie.
• Geslote sisteem: Vir reaksie om in ewewig te bly of om dinamiese ewewig te bereik, sisteem
gesluit moet word. Dus temperatuur, druk en konsentrasie of reaktante/produkte word nie beïnvloed nie
deur invloede van buite.

• Posisie van ewewig: Die relatiewe hoeveelhede reaktante en produkte, wat die omvang van
'n omkeerbare reaksie by ewewig.
• le Chatelier se beginsel: Wanneer 'n sisteem in dinamiese ewewig aan 'n eksterne verandering onderwerp word
in toestande sal die posisie van ewewig verskuif om die effek van verandering te minimaliseer.
• Op 'n grafiek bereik stelsel dinamiese ewewig wanneer konsentrasie konstant is.
• Ondersoek konsentrasie: Ekwilibrium tussen chromatieone CrO4
2-
(geel oplossing) en
dichromaatione Cr2O7
2-
(oranje oplossing) verander met suurkonsep so maklik om te sien skuif in
ewewig.
2CrO4
2-
(aq) + 2H+
(aq) ⇌ Cr2O7
2-
(aq) + H2O (l).
• Metode: Voeg geel kaliumchromaat K2CrO4 by. Voeg swaelsuur H2SO4 by tot geen verdere verandering nie.
Oplossing word oranje. Voeg waterige natriumhidroksied NaOH(aq) by tot geen verdere verandering nie.
Oplossings word weer geel.
• Toenemende reaktant:
– Wanneer verdunde swaelsuur bygevoeg word, verhoog die konsentrasie van H+ (aq) ione.
& # 8211 Verhoog tempo van vorentoe reaksie.
– Laat posisie van ewewig skuif na regs verminder verandering in H+
(aq) konsentrasie. Nuut
posisie van ewewig gevestig teenoor produkte. Oplossing word oranje soos Cr2O7
2-
.
• Afnemende reaktant:
– Wanneer voeg NaOH (aq), bygevoeg OH-
(aq) ione reageer met H+ (aq) ione om H2O te vorm. Dit neem af
konsentrasie van H+ (aq) ione, die reaktant.
& # 8211 Verminder tempo van vorentoe reaksie.
– Veroorsaak dat posisie van ewewig na links skuif om verandering in konsentrasie te minimaliseer. Nuut
posisie van ewewig word ingestel teenoor reaktant. Oplossing word geel soos CrO4
2-
gevorm.
• Temperatuur: Voorwaartse en terugwaartse reaksies het dieselfde waarde vir entalpieverandering, maar tekens is
teenoorgestelde.
• Ondersoek temperatuurmetode: Los kobaltchloried CoCl2 op. Voeg HCl by. Plaas kookbuis in
yswater. Oplossing is pienk kleur. Plaas kookbuis in waterbad. Oplossings word blou.
Verander pienk wanneer terug in yswater.
• Konsentrasie: HCl bygevoeg om meer Cl-
(aq) ione. Verskuif ewewig effens na regs
kleurveranderinge te bewerkstellig.
• Toenemende temperatuur:
– Toename in temperatuur, verskuif posisie van ewewig in die voorwaartse rigting in endotermiese
rigting.
– So om energie te absorbeer en toename in temperatuur te verminder.
– Meer produkte gemaak. Oplossing word blou.
• Afnemende temperatuur:
– Afnemende temperatuur, skuif die posisie van ewewig in die eksotermiese rigting.
– Meer reaktante gemaak.
• Druk: Slegs gasse. 2NO2 (g) ⇌ N2O4 (g). Stikstofdioksied het 2 mol en is bruin. Distikstof
tetroksied het 1 mol en is kleurloos.
• Toenemende druk:
– Toenemende druk sal die posisie van ewewig verskuif na die kant van minder mol gas op
die reaktant/produkkant.

– Vermindering van die aantal gasvormige mol om toename in druk te minimaliseer - kwoteer aantal mol.
Meer kleurlose N2O4 (g) het gevorm en bruin kleur vervaag.
• Afnemende druk: Bruin kleure verdiep.
• H2 + Br2 ⇌ 2HBR. Geen verandering vind plaas in posisie van ewewig wanneer 'n toename in druk as
dieselfde aantal moesies aan beide kante. PCl5 ⇌ PCl3 + Cl2, hier het die produk meer mol.
• Katalisator: Verander nie posisie van ewewig nie. Dit versnel voorwaartse en terugwaartse reaksies
ewe. Verhoog die tempo waarteen 'n ewewig tot stand kom. Katalise vind plaas by laer
temperature met 'n laer energievraag, verminder dus CO2-emissies/minder fossielbrandstowwe wat verbrand word.
• Haber-proses: N2 (g) + 3H2 ⇌ 2NH3 (g). le Chatelier se beginsel wat gebruik word om die beste toestande te voorspel
maksimum opbrengs lewer.
• 'n Lae temperatuur sal 'n hoë opbrengs van produk produseer, maar kan nie aktiveringsenergie oorkom nie
so stadige tempo van reaksie.
• Hoë druk verhoog nie net opbrengs nie, maar ook reaksietempo. Benodig egter groot hoeveelhede
energie so duur en ook veiligheidsrisiko's aangesien giftige ammoniak onder druk kan lek.
• Gebruik 'n sekere waarde vir hoë genoeg druk/temperatuur vir goeie reaksietempo sonder
kompromitterende opbrengs. Verhoogde temperatuur of druk, verhoog reaksietempo- sien ander
onderwerp. Kompromie- kies 'n hoër temperatuur wat verminderde opbrengs skep, maar in korter spasie
van tyd.
• Ongereageerde stikstof en waterstof herwin om in ammoniak omgeskakel te word.


Verandering in sintesetempo van 'n molekule verander ewewigskonsentrasie - Biologie

Hierdie afdeling is 'n uitbreiding van die chemiese ewewig bladsy. Jy moet gemaklik wees om basiese ewewigsberekeninge te doen om hierdie materiaal te verstaan.

Die reaksie van 'n ewewig op verandering

Dink aan 'n chemiese reaksie by ewewig. In die generiese reaksie

byvoorbeeld, hoe word die ewewig beïnvloed as ons:

verwyder een of ander produk D ?

voeg 'n produk by A ?

verhoog of verlaag die temperatuur ?

verhoog of verlaag die druk ?

Le Châtelier se beginsel sal ons help om die rigting van die ewewigsverskuiwing te voorspel wanneer veranderinge soos hierdie aan die reaksiemengsel gemaak word.

In hierdie afdeling gebruik ons ​​frases soos "verskuiwing na regs" of "verskuiwing na links." Wanneer 'n ewewig na regs skuif, produseer dit meer produk as voorheen wat dit ook al laat skuif het. Die teenoorgestelde is waar vir die verskuiwing na links (na reaktante).

Dink aan 'n wipplank wat in balans is. Sit nou 'n bietjie ekstra gewig aan die een kant. Jy sal gewig aan die ander kant moet byvoeg om balans te herwin. Chemiese reaksies maak dieselfde soort aanpassings outomaties, en Le Châtelier se beginsel sal ons help om dit te verstaan.

Le Châtelier se beginsel is vernoem na Henry Louis Le Châtelier, 'n Franse chemikus wat in 1936 op die ouderdom van 85 gesterf het. Weergawes van Le Châtelier se skoolhoof word in die ekonomie gebruik om die rigting waarin ekonomiese aanwysers sal verskuif te voorspel. sekere veranderinge.

Le Châtelier se beginsel

Enige verandering wat in 'n sisteem by chemiese ewewig plaasvind, veroorsaak 'n aanpassing in die konsentrasies van reaktant(e) of produk(te) wat die ewewig herstel.

'n Analogie

Dink aan 'n massa wat aan 'n veer hang. Wanneer ons strek die lente weg van sy ewewigsposisie ('n perfekte balans tussen die gravitasiekrag wat die massa aftrek en die trekkrag van die veer), probeer 'n herstelkrag om dit terug te trek na ewewig. Soos die veer saamgepers word, probeer 'n ander herstelkrag om dit na ewewig uit te brei (EQ in die animasie).

Ek het hierdie veer op sy sy gesit sodat swaartekrag in die links-regs rigting sal moet werk, maar jy kry die idee. Chemiese reaksies tree baie op dieselfde manier op: Afhangende van die versteuring van ewewig, sal die stelsel aanpas in die rigting om ewewig te herwin.

Konsentrasie verander

Wat ons hier wil verstaan, is wat die effek van die verandering van die konsentrasie van een reaksie komponent is op al die ander. Kom ons begin baie eenvoudig met 'n omkeerbare reaksie wat een of ander molekule omskakel A aan B en B terug na A:

Die ewewigskonstante uitdrukking is maklik om te skryf:

Kom ons oorweeg dit nou om 'n paar veranderinge aan die reaksiemengsel te maak sodra dit in ewewig is.

1. Verwyder een of ander produk

Stel jou voor dat sodra die mengsel ewewig bereik het, ons 'n produk kan verwyder, B. Deur dit te doen, sal die ewewig versteur, en dit sal meer aanpas A omskakeling na B totdat die ewewig weer ingestel is.

2. Voeg 'n bietjie reaktant by

Die byvoeging van reaktant het dieselfde effek as om beide produk te verwyder skuif die reaksie na regs, na produk.

3. Verwyder 'n paar reaktant

Die verwydering van reaktant, A, veroorsaak dat die terugwaartse reaksie toeneem. Genoeg B keer terug na A sodat ekwilibrium weer ingestel word.

4. Voeg 'n produk by

Die byvoeging van produk veroorsaak ook 'n versteuring in die ewewig wat die reaksie sal dryf aan die linkerkant, terug na reaktante.

Veralgemening na meer ingewikkelde reaksies

Hierdie beginsels is dieselfde vir meer ingewikkelde reaksies soos

Die byvoeging van reaktant(e) of die verwydering van produk(te) veroorsaak dat die ewewig na regs skuif.

Die verwydering van reaktant(e) of byvoeging van produk(te) veroorsaak dat die ewewig na links verskuif.

Hierdie idees kan baie belangrik wees in alle soorte chemie. Oorweeg byvoorbeeld 'n reaksie waarin jy 'n produk wil (en kan) voortdurend verwyder, iets wat jy graag wil hê. Dan is die verwydering van produk en die byvoeging van reaktante 'n manier om die reaksie voortdurend na regs te laat beweeg, na die produk(te) wat jy graag wil vorm.

Effekte van konsentrasieveranderinge op ewewig

Vir enige chemiese reaksie by ewewig,

Die byvoeging van reaktant(e) of die verwydering van produk(te) veroorsaak dat die ekwilibrium na regs skuif, na produkte.

Die verwydering van reaktant(e) of byvoeging van produk(te) veroorsaak dat die ewewig na links skuif, na reaktante.

Dit gebeur nie oombliklik nie

Ons moet dink oor wat werklik met verloop van tyd gebeur as 'n sisteem in chemiese ewewig versteur word, en dan beweeg om ewewig te hervestig.

Oorweeg om die konsentrasie van 'n reaktant te verander, A. As [A]o is die aanvanklike ewewig konsentrasie van A, voeg dan by A vinnig sal vinnig die konsentrasie van verhoog A. Maar dit sal die ewewig versteur en meer veroorsaak A om te reageer om produkte te vorm en sodoende die konsentrasie daarvan te verminder.

Die nuwe konsentrasie van A sal wees [A]'. Let op dat die nuwe konsentrasie nie (kan nie dieselfde wees as die ou konsentrasie nie. Dit sal 'n bietjie styg.

Kom ons doen 'n voorbeeldberekening en kyk of ons die veranderinge in alle komponente van die ewewig kan volg

Kom ons laat Kvgl = 0.25 (lukraak gekies, net vir hierdie generiese voorbeeld), dan is die ewewigskonstante uitdrukking:

Nou vir eenvoud, laat ons

Vervolgens bou ons 'n ICE-tabel:

$ egin & onderstreep & onderstreep & onderstreep [3pt] [A] & 1.0 & -x & 1-x [3pt] [B] & 1.0 & -x & 1-x [3pt] [C] & 0 & +x & x [3pt] [D] & 0 & +x & x end$

Albei kante is vierkante, so die vierkantswortel van albei kante gee:

'n Bietjie herrangskikking en 'n paar maklike algebra gee ons

$ egin x &= 0.5 - 0.5 x 1.5 x &= 0.5 x &= 0.33 end$

en ons finale stel ewewigskonsentrasies is

$ egin [A] &= 0.67 [B] &= 0.67 [C] &= 0.33 [D] &= 0.33 end$

Kom ons maak nou 'n verandering. Ons sal vinnig die konsentrasie van verhoog A van 1 tot 2 (Ek gebruik nie eenhede hier net om dinge eenvoudig te hou nie). Die nuwe ICE-tafel is

$ egin & onderstreep & onderstreep & onderstreep [3pt] [A] & color<#E90F89> <2.0>& -x & 2-x [3pt] [B] & 1.0 & -x & 1-x [3pt] [C] & 0 & +x & x [3pt] [D] & 0 & +x & x end$

Deur die ewewigswaardes in die ewewigskonstante uitdrukking te koppel, gee ons 'n effens meer ingewikkelde uitdrukking, maar dit is steeds doenbaar:

Uitbreiding van die noemer gee

Nou vermenigvuldig ons beide kante met daardie noemer

en versamel terme om 'n mooi kwadratiese vergelyking te kry:

En ons nuwe stel ewewigskonsentrasies is

$ egin [A] &= 1.54 [B] &= 0.54 [C] &= 0.457 [D] &= 0.457 end$

Nou kan ons 'n diagram konstrueer wat modelleer wat gebeur as die ewewig weer ingestel word na die byvoeging van meer A. Dit kan dalk so lyk:

Kyk of jy die verloop van die reaksie uit die oogpunt van elk van die komponente kan volg. Let op dat die konsentrasie van A is groter as voorheen die byvoeging van meer A, maar dat sommige daarvan met meer gereageer het B om toenames in die konsentrasies van te produseer C en D.

Dinge kan 'n bietjie meer ingewikkeld raak wanneer die reaksiekoëffisiënte groter as 1 is, maar die algemene idee is dieselfde. Daar is 'n kort tyd wanneer die reaksie buite balans is, totdat dit ewewig bereik, en op daardie stadium sal alle komponente 'n ander ewewigskonsentrasie as voorheen hê.

Oefen probleme

Voorspel die rigting van die ewewigsverskuiwing. Rol oor/tik op die vraag om die antwoord te sien.

vind plaas wanneer 'n gaskoeldrankbottel oopgemaak word. In watter rigting word die ewewig verskuif wanneer die bottel oopgemaak word, en hoekom?

Wanneer die bottel oopgemaak word, CO2 ontsnap in die atmosfeer (dit is die gesis wat jy hoor wanneer jy 'n koeldrankbottel of -blik oopmaak). Die verwydering van die produk sal die ewewig na regs verskuif.

As ons die ewewigsuitdrukking neem,

en herrangskik dit so:

dit is maklik om dit te sien as die konsentrasie van CO2 verminder (omdat dit die mengsel verlaat), die konsentrasies suur (H3O + ) en HCO3 + verminder. Laasgenoemde kan dit slegs doen deur die reaksie na regs te gaan.

Die sintese van ammoniak (NH3) word bewerkstellig in 'n proses bekend as die Haber-proses. Die basiese reaksie is

(a) Bereken die ewewigparsiële druk van alle komponente as PN2 = 1 atm. en PH2 = 1.0 atm. (b) Bereken nuwe ewewig-parsiële drukke as die helfte van die ammoniak uit die ewewigsmengsel verwyder word.

Ons ewewigsuitdrukking vir hierdie reaksie is

Ons ewewig ICE tabel lyk soos volg:

Ons bly dus oor om hierdie vergelyking vir x op te los:

Ons kan dit numeries op 'n sakrekenaar doen deur hierdie eenvoudige herrangskikking te maak,

en vind eenvoudig die kruising(e). Hierdie grafiek van 'n TI84 sakrekenaar toon twee kruisings.

Die regterkantste gee x > 1, wat nie kan gebeur nie, so ons gooi daardie oplossing weg. Die linker oplossing gee x = 0,231, so ons ewewigsbedrae is:

As ons nou die helfte van die ewewigsdruk van ammoniak verwyder (NH3), wat 0,231 atm is, reël ons 'n nuwe tafel:

Net so moet ons nou hierdie vergelyking oplos:

'n Soortgelyke berekening gee x = 0,032. Deur ons tabel te gebruik, verkry ons die nuwe ewewigswaardes:

Jy kan sien dat die verwydering van die produk gelei het tot die vorming van meer ammoniak. Die Haber-proses werk deur voortdurende verwydering van ammoniak en hertoevoer van H2 en N2 om 'n konstante stroom van produk te vorm.

Effek van temperatuur op ewewig

Noudat jy vertroud is met hoe veranderinge in konsentrasie ewewigte beïnvloed, is dit redelik eenvoudig om uit te vind hoe temperatuurveranderinge hulle sal beïnvloed.

Die sleutel is om te behandel hitte as 'n reaktant of produk, wat ook al geskik is vir die termodinamika van die proses. Hier is wat daarmee bedoel word.

Dit is bekend dat hierdie reaksie eksotermies is, so ons kan hitte as 'n ander produk behandel, en die reaksie soos volg skryf:

Oorweeg nou wat gebeur wanneer ons hierdie reaksiemengsel verhit. Die ewewig sal na links skuif, net asof hitte was 'n chemiese produk en ons het meer bygevoeg.

Aan die ander kant, as ons hierdie reaksie afkoel, wat beteken dat ons hitte verwyder, sou ons 'n produk verwyder, en ons sou verwag dat die reaksie-ewewig na regs sou beweeg. Dit is redelik handig om te weet of jou doel is om soveel CS te maak2 as moontlik & # 8211 net koel die reaksie af 'n bietjie.

'n Endotermiese reaksie

Beskou nou die endotermiese reaksie, die oplos van ammoniumchloried in water:

As ons hierdie keer hitte byvoeg, voorspel ons dat die reaksie na regs sal skuif om weer te ewewig. En as ons die mengsel afkoel, deur 'n " reaktant" te verwyder, sou ons verwag dat die ewewig na links sal skuif, na reaktante.

In hierdie geval, om meer ammoniumchloried op te los, wil ons die mengsel verhit.

Om die effek van temperatuur op 'n reaksie-ewewig te voorspel, beskou die hitte wat verkry word (endotermiese reaksies) of die hitte geproduseer deur (eksotermies) die reaksie as 'n reaktant of a produk, soos toepaslik. Toenemende temperatuur dra dan by tot hitte en vermindering daarvan verminder die hoeveelheid bygevoegde hitte.

Oefen probleme

Oorweeg die eksotermiese reaksie

Wat sou met die ewewig gebeur as

(a) Is die reaksiemengsel verhit?
(b) Is stoom bygevoeg?
(c) Is die temperatuur verlaag?

(a) Omdat die reaksie eksotermies is, is hitte 'n produk. Die byvoeging van produkte veroorsaak dat die reaksie na links beweeg, so verhitting van hierdie reaksie sal 'n verskuiwing na reaktante veroorsaak.

(b) Stoom kan 'n mengsel van gasvormige en vloeibare water wees. As dit warm genoeg is, is dit alles H2O gas, wat die reaksie na regs sal beweeg. Aan die ander kant kan die byvoeging van warm stoom die reaksiemengsel so verhit dat dit die ewewig na links beweeg (sien (a) hierbo).

(c) Verlaging van die temperatuur beteken die verwydering van hitte. Omdat hitte 'n produk van 'n eksotermiese reaksie is, behoort afkoeling van die reaksie die ewewig na produkte te beweeg.

Oorweeg die endotermiese oplossing van ureum in water

(a) Wat sou gebeur as die temperatuur verhoog is?
(b) As die temperatuur verlaag is?

(a) Hierdie reaksie is endotermies, wat beteken dat hitte as 'n reaktant beskou kan word. Die byvoeging van hitte behoort dan die ewewig na regs, na die produk toe te beweeg.

(b) Net so, as die temperatuur verlaag word, behoort die ewewig na links te skuif.

Verandering van die druk van 'n gasvormige ewewigsmengsel

Die effek van die verandering van druk op 'n ewewig is 'n bietjie moeiliker. Ons verdeel dit in twee dele,

(1) die byvoeging van 'n nie-reaktiewe gas om die druk te verhoog, en

(2) die verhoging van die druk van 'n ewewigsmengsel deur die volume daarvan te verminder.

Voeg nie-reaktiewe gasse by

Dink aan 'n gasmengsel in ewewig. Die konsentrasie van elke gas kan uitgedruk word deur die ideale gaswet,

n is die aantal mol, dus n/v is die molêre konsentrasie, en P is die gedeeltelik druk van die gas van belang. Onthou dit R is die molêre gaskonstante (R = 0,0812 J·mol -1 K -1) en T is die Kelvin-temperatuur.

Die konsentrasie van elke gas is verwant aan sy eie parsiële druk, en nie die totale druk, dus die verhoging van die totale druk deur bloot ander gasse in te voer (solank hulle nie die ewewig inmeng deur met enige van die bestanddele te reageer nie), behoort nie die ewewig te beïnvloed nie.

Daar is natuurlik perke hieraan. Soms kan die byvoeging van 'n inerte gas die waarskynlikheid van drieliggaambotsings verhoog, waarin die inerte deeltjie oortollige energie kan wegdra wat 'n reaksie laat plaasvind, sodat reaksietempo's beïnvloed kan word, soms differensieel (meer vorentoe as agtertoe, byvoorbeeld ).

Verander die volume

Die parsiële druk van elke komponent van 'n gasmengsel is

'n Toename in volume verminder die gedeeltelike druk van elke komponent, en 'n afname in volume verhoog die gedeeltelike druk.

Oorweeg die eenvoudige reaksie

Een mol van A en B produseer een mol elk van C en D. In hierdie geval verander 'n verandering in volume elke gedeeltelike druk, PA, PB, PC en PD, in dieselfde verhouding, so daar sal nie 'n verandering in die ewewig wees nie.

Maar oorweeg 'n ander reaksie

In hierdie geval produseer twee mol reaktante drie mol produk, en daar sal 'n verskil in parsiële druk wees met 'n verandering in volume omdat die aantal mol, n is verskillend.

Aan die linkerkant van hierdie vergelyking is daar twee mol gas, maar aan die regterkant is daar drie. 'N Verandering in volume sal die parsiële druk van elke gas beïnvloed in verhouding tot sy koëffisiënt – die aantal mol teenwoordig in die reaksie. Wanneer die volume van hierdie reaksie verminder word, word die parsiële druk van C sal vinniger toeneem as dié van A of B, dus sal die reaksie-ewewig na links, na produkte en na minder mol neig.

Omgekeerd, wanneer die volume verhoog word, sal die gedeeltelike druk aan die regterkant vinniger afneem as dié aan die linkerkant, wat die reaksie na regs dwing.

Kom ons doen 'n voorbeeld om hierdie idee verder te illustreer.

Voorbeeld 1

Oorweeg die sintese van ammoniak,

As die volume tienvoudig verminder word, in watter rigting sal die reaksie aanpas om ewewig te handhaaf?

Oplossing : Kom ons laat PN2, PH2 en PNH3 wees die ewewig parsiële druk van stikstof, waterstof en ammoniak, onderskeidelik by ewewig.

Die ewewigskonstante uitdrukking is

Nou volgens die ideale gaswet is die parsiële druk van 'n komponent van 'n gasmengsel

R is 'n konstante en as ons die temperatuur konstant hou, is die parsiële druk eweredig aan die aantal mol gedeel deur die volume (die konsentrasie):

As die volume nou verminder word, sal die parsiële druk van komponente van die reaksiemengsel toeneem of afneem in verhouding tot die aantal mol teenwoordig. In die geval van ammoniak sintese, PNH3 en PH2 sal vinniger styg as PN2.

Hier is 'n blik op die gedeeltelike druk van ons drie komponente aangesien die volume van 1L (regterkant van die grafiek) tot 0.1L (linkerkant) verminder word. Let daarop dat ongeveer 0.2L volume, PNH3 kruis die PN2 kromme. Dus by hoë druk word die produk bo die reaktante bevoordeel, of die ewewig skuif na regs, na die kant toe met minder totale mol.

Daar is 'n eenvoudige stel reëls om te voorspel hoe ewewigte met verskillende totale aantal mol reaktante en produkte sal optree by veranderinge in volume (en dus druk):

Wanneer die volume is afgeneem, beweeg die ewewig na die kant met minder mol.

Wanneer die volume is toegeneem, beweeg die ewewig na die kant met meer totale mol.

Ewewig en volume verander

Vir 'n gasmengsel by ewewig, waarin die totale aantal mol reaktant(e) is anders as die totale aantal mol produk(te),

Wanneer die volume is afgeneem, die ewewig beweeg in die rigting van die kant met minder totale mol, en

wanneer die volume is toegeneem, die ewewig beweeg in die rigting van die kant met meer totale mol.

Byvoeging van 'n katalisator

'n Katalisator is iets wat die tempo van 'n chemiese reaksie verhoog. Katalisators het egter geen effek op ewewig nie, want hulle verhoog beide die voorwaartse en terugwaartse tempo van chemiese reaksie. Dit klink nie of daar veel te baat is by die gebruik van 'n katalisator nie, maar oorweeg die meeste van die chemiese reaksies wat in selle plaasvind.

Oorgelaat aan hul eie sonder katalisators (wat ons ensieme in biologie noem), sou die meeste biochemiese prosesse nooit gebeur nie. Dis hoe stadig hulle is. Katalisators versnel dus reaksies, wat soms selfs toelaat dat hulle enigsins plaasvind.

Ekwilibrium is 'n feit van omkeerbare chemiese reaksies waarmee ons altyd moet klaarkom.


LE CHATELIER SE BEGINSEL

Die le Chatelier se beginsel kan gestel word as:

Wanneer eksterne spanning op 'n sisteem by dinamiese ewewig toegepas word, verskuif die stelsel die posisie van ewewig om die effek van spanning te vernietig.

Stres kan op chemiese sisteme toegepas word deur die konsentrasie of druk of temperatuur te verander. Dit kan dus gestel word as:

Wanneer 'n chemiese sisteem by dinamiese ewewig versteur word deur die konsentrasie van óf reaktante óf produkte te verander of deur die parsiële druk van enige van gasvormige reaktante of van gasvormige produkte of temperatuur te verander, word die posisie van ewewig in daardie rigting verander om 'n nuwe ewewigstoestand dit wil sê, óf voorwaartse reaksie óf terugwaartse reaksie word bevoordeel.

7) Toets jou begrip - MCQ

EFFEK VAN VERANDERING IN KONSENTRASIE

Die verandering in konsentrasie kan slegs gasstelsels of vloeibare oplossingstelsels beïnvloed. Dit beïnvloed egter nie die vaste- en suiwervloeistofstelsels nie, aangesien hul aktiewe massas altyd as eenheid beskou word.

Deur le Chatelier se beginsel te gebruik, kan die effek van verandering in konsentrasie op sisteme by ewewig soos volg verduidelik word:

1) Wanneer die konsentrasie van reaktant(e) word verhoog, probeer die stelsel om hul konsentrasie te verminder deur die voorwaartse reaksie te bevoordeel.

2) Wanneer die konsentrasie van produk(te) verhoog word, probeer die stelsel om hul konsentrasie te verminder deur die terugwaartse reaksie te bevoordeel.

3) Wanneer die konsentrasie van reaktant(e) word verminder, probeer die stelsel om hul konsentrasie te verhoog deur die terugwaartse reaksie te bevoordeel.

4) Wanneer die konsentrasie van produk(te) word verminder, probeer die stelsel om hul konsentrasie te verhoog deur die voorwaartse reaksie te bevoordeel.

Wanneer die konsentrasie van reaktante verhoog word, neem die aantal effektiewe botsings tussen hulle toe wat weer die tempo van voorwaartse reaksie verhoog. Die voorwaartse reaksie word dus meer bevoordeel bo die terugwaartse reaksie totdat die nuwe ewewig gevestig is. By hierdie nuwe ewewig word die tempo van beide voorwaartse en terugwaartse reaksies weer gelyk en die reaksiekwosiënt word ongeveer gelyk aan die ewewigskonstante.

Onthou dat klein veranderinge in konsentrasie nie die ewewigskonstante noemenswaardig beïnvloed nie.

Die ontbinding van gasvormige PCl5 is 'n omkeerbare reaksie.

Laat die ewewigskonsentrasies van PCl5, PCl3 en Cl2 is onderskeidelik [PCl5], [PCl3] en [Cl2]. Die KC want hierdie reaksie kan geskryf word as:

Ons weet ook dat by ewewig KC = Q.

Laat die konsentrasie van PCl5 word verdubbel om die ewewig te versteur. Dit sal die reaksiekwosiënt, Q verander na:

Nadat die ekwilibrium versteur is, word die waarde van Q minder as KC. Om die Q-waarde na K te herstelC, die konsentrasie van PCl5 moet verminder word terwyl die konsentrasies van PCl3 en Cl2 verhoog moet word. Dit word bereik deur die voorwaartse reaksie te bevoordeel.

Die voorwaartse reaksie word ook bevoordeel deur die produkte uit die reaksiemengsel te verwyder (afname in die konsentrasie van produkte). By die verwydering van produkte word die tempo van voorwaartse reaksie kortstondig groter as dié van terugwaartse reaksie. Dit sal ook die reaksiekwosiënt verlaag. Daarom probeer die stelsel om die ewewig te herstel deur meer reaktante na produkte om te skakel sodat die tempo van beide voorwaartse en terugwaartse reaksies weer gelyk word.

Byvoorbeeld, in die geval van die ontbinding van PCl5, indien die konsentrasie van Cl2 met twee keer verhoog word by ewewig, word die Q-waarde groter as die KC waarde.

Daarom probeer die stelsel om die waarde van Q na K te herstelC weer. Die terugwaartse reaksie word bevoordeel om die konsentrasie van Cl te verlaag2. Die konsentrasie van PCl5 neem ook outomaties af terwyl die konsentrasie van PCl5 verhoog terwyl dit gedoen word.

EFFEK VAN VERANDERING IN DRUK

Die verandering in druk beïnvloed slegs die ewewig van stelsels wat ten minste een gas behels. Die le Chatelier se beginsel kan soos volg toegepas word om die effek van verandering in druk op die stelsels by ewewig te verstaan.

1) Wanneer die gedeeltelike druk van enige van die gasvormige reaktante of van die produkte is toegeneem, word die posisie van ewewig so verskuif om verminder sy gedeeltelike druk. Dit word gewoonlik bereik deur die reaksie te bevoordeel waarin daar afname in die aantal mol gasvormige komponente is.

2) Wanneer die gedeeltelike druk van enige van die gasvormige reaktante of van die produkte is afgeneem, word die posisie van ewewig so verskuif om verhoog sy gedeeltelike druk. Dit kan bereik word deur die reaksie te bevoordeel waarin daar 'n toename in die aantal mol gasvormige komponente is.

Dit is egter nie altyd korrek om te sê dat die ewewig verskuif word wanneer daar 'n verandering in die totale druk van die sisteem is nie. Die ewewig word nie altyd versteur wanneer die druk van die hele sisteem verander word nie. Dit word slegs versteur wanneer daar 'n verandering in die parsiële druk van enige of al die gasvormige reaktante of produkte in die ewewig is waarvoor &Deltang &ne 0.

Waar &Deltang = (aantal mol gasvormige produkte) - (aantal mol gasvormige reaktante)

Streng gesproke word die ewewig slegs verskuif wanneer die verhouding van produk van parsiële druk van produkte tot die produk van parsiële druk van reaktante d.w.s. die reaksiekwosiënt in terme van parsiële druk, Qbl is versteur. Die posisie van ewewig word verskuif om Q te maakbl gelyk word aan die waarde van Kbl weer.

Die Qbl kan in die volgende gevalle verander word:

1) Deur enige gasvormige reaktant of produk teen konstante volume by te voeg of te verwyder. Die effek is dieselfde as om die konsentrasie te verander soos hierbo verduidelik.

2) Deur die volume van die sisteem te verander (of met ander woorde deur die druk van die hele sisteem te verander) by ewewig waarvoor die &Deltang &ne 0. In hierdie geval word die druk van die hele stelsel egter ook verander.

Vir die ontbinding van PCl5, die Kbl kan geskryf word as:

Dus vir hierdie reaksie, as die druk van die sisteem met 2 keer verhoog word deur die volume te halveer, die reaksiekwosiënt, Qbl word verander na:

Om die Qbl waarde weer aan Kbl, the denominator value i.e., the partial pressure of PCl5 must be increased. This is only achieved by favoring the forward reaction in which less number of gaseous products are formed. i.e., Two moles of products (PCl3 en Cl2) are converted to one mole of reactant (PCl5)

Therefore we can say, at least in this case, if the pressure of the system is increased, the system tries to decrease it by favoring the reaction in the direction of decreasing the number of moles of gaseous components.

3) By adding a non reacting inert gas to the system at constant pressure when &Deltang &ne 0: The addition of an inert gas at constant pressure increases the volume of the system. Hence the partial pressures of gaseous components are decreased. This will disturb the Qp value. Hence the system tries to restore the Qp to Kp.

Whereas, the Qp value cannot be changed in the following cases:

1) By changing the volume of the system (or in other words by changing the pressure of entire system) at equilibrium for which &Deltang = 0. Hence the position of equilibrium is not going to be changed.

Let us consider the decomposition of HI to H2 and I2.

For this reaction, the &Deltang = (1+1) - (2) = 0.

The Kp can be written for this equilibrium as:

If the volume of the system is halved to double the pressure, the Qp value is not changed as illustrated below.

In this case, the increase in the product of partial pressures of products (the numerator value) is nullified by the increase in the product of partial pressures of reactants (the denominator value).

Therefore, when &Deltang = 0, there is no effect of changing the pressure of entire system.

However, remember that if the partial pressures of gaseous components are changed to different extent, the equilibrium is disturbed even if &Deltang = 0.

2) By adding a non reacting inert gas to the system at constant volume. In this case, the pressure of the entire system is increased. However the individual partial pressures of gases participating in the reaction are not changed since the volume is not changed. Hence the Qp value does not change. That is why there will be no effect of adding an inert gas to the system at constant volume.

3) By adding a non reacting inert gas to the system at constant pressure when &Deltang = 0 . The volume of the system is increased when a non reacting gas is added to the system at constant pressure. This will decrease the partial pressures of each gaseous component. However the Qp value is not disturbed since the decrease in the numerator value is cancelled by the decrease in the denominator value.

However any reacting gas can disturb the equilibrium.

EFFECT OF CHANGE IN TEMPERATURE

The effect of temperature can be understood by using le Chatelier's principle as follows:

1) Increase in the temperature of the system favors the endothermic reaction.

The increase in temperature increases the amount of heat in the system. Hence it tries to remove the excess of heat by favoring that reaction in which heat is absorbed i.e., the endothermic reaction.

2) Decrease in the temperature of the system favors the exothermic reaction.

In this case, the temperature is decreased by removing the heat content from the system. Hence the system tries to restore the temperature back by favoring the exothermic reaction i.e., the reaction in which the heat is liberated.

It is very important to note that, during the change in temperature, the system establishes a new equilibrium for which the value of equilibrium constant is different from the original constant i.e., the equilibrium constant depends on the temperature.

Consider the following exothermic reversible reaction:

In general, when we say a reaction is exothermic, the forward reaction is exothermic whereas, the backward reaction is endothermic.

This reaction can also be written as

The negative sign of &DeltaH indicates the exothermic nature of the forward reaction.

It is quite helpful to consider the 'heat' as one of the product of the reaction.

The equilibrium constant, KC can be written as:

If the equilibrium is disturbed by increasing the temperature by adding heat, the endothermic backward reaction is favored to remove the heat from the system. While doing so, the concentration of 'B' decreases and a new equilibrium position is established for which the new equilibrium constant, K'C can be written as:

If the temperature is decreased by removing the heat from the system, the system tries to increase the heat content by favoring the exothermic forward reaction. In this case, the new equilibrium constant, let us say K"C is greater than the KC.

EFFECT OF CATALYST

A catalyst has no effect on the position of the equilibrium since it increases not only the rate of forward reaction but also the rate of backward reaction. However it does help the system to reach the equilibrium faster.

The CoCl2.6H2O or [Co(H2O)6]Cl2 is a deep purple colored solid. It forms a purple colored solution when is dissolved in water. The color of [Co(H2O)6] 2+ ion is pink. However it exists in equilibrium with small amount of [CoCl4] 2- that is intense blue in color. The equilibrium is shown below. The purple color of the solution is the result of combination of these two colors.

The purple color of the aqueous solution of Cobalt(II) chloride can be changed by adjusting different variables in the following experiments.

1) The color of the solution turns intense blue upon addition of conc. HCl to the first test tube.

This is because of increase in the concentration of Cl - ions, which are furnished by HCl. As a result, the forward reaction is favored to give more [CoCl4] 2- . Hence the color is turned to intense blue.

The Cl - ions are common to both HCl and [Co(H2O)6]Cl2. Hence this is also referred to as "common ion effect".

2) The color of the solution turns to pale pink by adding excess of water in the second experiment.

According to le Chatelier's principle, the backward reaction is favored when the concentration of one of the product increases. Hence increase in the concentration of water favors backward reaction. That will result in the formation of more [Co(H2O)6] 2+ , which is pale pink in color.

3) In the third experiment, the color turns to blue upon heating the purple colored solution.

According to le Chatelier's principle, when heat is added to the system, the endothermic reaction is favored to remove heat from the system. In this case, the formation of [CoCl4] 2- is an endothermic reaction. Hence more amount of blue colored [CoCl4] 2- is formed.

Note: The intense blue color of [CoCl4] 2- is due to its tetrahedral geometry. You will learn this in more detail at advanced level of inorganic chemistry.

Try your self to answer the question: What will happen to the color when small amount of aqueous solution of AgNO3 is added to the first test tube?

HABER PROCESS

In Haber process, the ammonia is synthesized by combining pure nitrogen and hydrogen gases in 1:3 ratio in presence of finely powdered iron catalyst and molybdenum promoter at around 450 o C and at about 250 atm. of pressure.

The le Chatelier's principle helps in choosing these conditions to improve the yields of ammonia as explained as below.

Effect of pressure: In the forward reaction (synthesis of ammonia), the number of moles of gaseous components is decreasing.

Hence the synthesis of ammonia is favored by increasing the pressure of the system. Industrially, 100 - 250 atm. of pressure is employed.

Effect of temperature: Since the forward reaction is exothermic, the increase in temperature favors the backward reaction i.e., the dissociation of ammonia. That means according to le Chatelier's principle, the synthesis of ammonia is favored at lower temperatures. However the reaction will be too slow at lower temperatures (a kinetic restriction). Hence this reaction is carried out at optimal temperatures i.e., at about 450 - 550 o C to overcome the kinetic barrier.

Removal of ammonia: The forward reaction can also be favored by removing ammonia from the system from time to time by liquefying it.

Catalyst: To increase the speed of the reaction, finely powdered or porous iron is used as catalyst. Its efficiency can be improved by adding molybdenum or oxides of potassium and aluminium.

CONTACT PROCESS

In the contact process, sulfuric acid, the king of chemicals, is manufactured on large scale. The major steps involved in the process are:

The crucial step is the oxidation of sulfur dioxide, SO2 to sulfur trioxide, SO3. It is a reversible reaction. At normal conditions, the equilibrium lies far to the left and the amount of sulfur trioxide formed is very small. To improve the yield of sulfur trioxide, the reaction is carried out at around 450 o C and 2 atm pressure in presence of V2O5 or Pt, which acts as a catalysts.

These conditions are chosen by applying le Chatelier's principle as explained below.

Effect of pressure: In the forward reaction (formation of sulfur trioxide), the number of moles of gaseous components is decreasing.

Hence the forward reaction is favored by increasing the pressure of the system. However, at high pressures, the iron towers used in the contact process are corroded. Hence the process is carried out at optimal pressures like 2 atm.

Effect of temperature: Since the forward reaction is exothermic, at higher temperatures the backward reaction i.e., the dissociation of sulfur dioxide is more favored. However the reaction will be too slow at lower temperatures. Hence this reaction is carried out at optimal temperatures i.e., around 450 o C.

Catalyst: To increase the speed of the reaction, V2O5 or Pt are used as catalysts.


Chemistry for the gifted and talented: rates and equilibria

This activity demonstrates the links between the topics of rates of reaction and the equilibrium law. It provides students with an explanation of the equilibrium law and helps them explain why Le Chatelier’s principle works for temperature, concentration and pressure.

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The equilibrium constant for step 1 is k1and for step 2 is k2

The equilibrium constant for step 1 is K1and for step 2 is K2

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Inhoud

Le Chatelier's principle describes the qualitative behavior of systems where there is an externally induced, instantaneous change in one parameter of a system it states that a behavioral shift occurs in the system so as to oppose (partly cancel) the parameter change. The duration of adjustment depends on the strength of the negative feedback to the initial shock. Where a shock initially induces positive feedback (such as thermal runaway), the new equilibrium can be far from the old one, and can take a long time to reach. In some dynamic systems, the end-state cannot be determined from the shock. The principle is typically used to describe closed negative-feedback systems, but applies, in general, to thermodynamically closed and isolated systems in nature, since the second law of thermodynamics ensures that the disequilibrium caused by an instantaneous shock must have a finite half-life. [5] The principle has analogs throughout the entire physical world.

While well rooted in chemical equilibrium and extended into economic theory, Le Chatelier's principle can also be used in describing mechanical systems in that a system put under stress will respond in such a way as to reduce or minimize that stress. Moreover, the response will generally be via the mechanism that most easily relieves that stress. Shear pins and other such sacrificial devices are design elements that protect systems against stress applied in undesired manners to relieve it so as to prevent more extensive damage to the entire system, a practical engineering application of Le Chatelier's principle.

Effect of change in concentration Edit

Changing the concentration of a chemical will shift the equilibrium to the side that would counter that change in concentration. The chemical system will attempt to partly oppose the change affected to the original state of equilibrium. In turn, the rate of reaction, extent, and yield of products will be altered corresponding to the impact on the system.

This can be illustrated by the equilibrium of carbon monoxide and hydrogen gas, reacting to form methanol.

Suppose we were to increase the concentration of CO in the system. Using Le Chatelier's principle, we can predict that the concentration of methanol will increase, decreasing the total change in CO. If we are to add a species to the overall reaction, the reaction will favor the side opposing the addition of the species. Likewise, the subtraction of a species would cause the reaction to "fill the gap" and favor the side where the species was reduced. This observation is supported by the collision theory. As the concentration of CO is increased, the frequency of successful collisions of that reactant would increase also, allowing for an increase in forward reaction, and generation of the product. Even if the desired product is not thermodynamically favored, the end-product can be obtained if it is continuously removed from the solution.

The effect of a change in concentration is often exploited synthetically for condensation reactions (i.e., reactions that extrude water) that are equilibrium processes (e.g., formation of an ester from carboxylic acid and alcohol or an imine from an amine and aldehyde). This can be achieved by physically sequestering water, by adding desiccants like anhydrous magnesium sulfate or molecular sieves, or by continuous removal of water by distillation, often facilitated by a Dean-Stark apparatus.

Effect of change in temperature Edit

The effect of changing the temperature in the equilibrium can be made clear by 1) incorporating heat as either a reactant or a product, and 2) assuming that an increase in temperature increases the heat content of a system. When the reaction is exothermic (ΔH is negative and energy is released), heat is included as a product, and when the reaction is endothermic (ΔH is positive and energy is consumed), heat is included as a reactant. Hence, whether increasing or decreasing the temperature would favor the forward or the reverse reaction can be determined by applying the same principle as with concentration changes.

Take, for example, the reversible reaction of nitrogen gas with hydrogen gas to form ammonia:

Because this reaction is exothermic, it produces heat:

If the temperature were increased, the heat content of the system would increase, so the system would consume some of that heat by shifting the equilibrium to the left, thereby producing less ammonia. More ammonia would be produced if the reaction were run at a lower temperature, but a lower temperature also lowers the rate of the process, so, in practice (the Haber process) the temperature is set at a compromise value that allows ammonia to be made at a reasonable rate with an equilibrium concentration that is not too unfavorable.

In exothermic reactions, an increase in temperature decreases the equilibrium constant, K, whereas in endothermic reactions, an increase in temperature increases K.

Le Chatelier's principle applied to changes in concentration or pressure can be understood by giving K a constant value. The effect of temperature on equilibria, however, involves a change in the equilibrium constant. The dependence of K on temperature is determined by the sign of ΔH. The theoretical basis of this dependence is given by the Van 't Hoff equation.

Effect of change in pressure Edit

The equilibrium concentrations of the products and reactants do not directly depend on the total pressure of the system. They may depend on the partial pressures of the products and reactants, but if the number of moles of gaseous reactants is equal to the number of moles of gaseous products, pressure has no effect on equilibrium.

Changing total pressure by adding an inert gas at constant volume does not affect the equilibrium concentrations (see Effect of adding an inert gas below).

Changing total pressure by changing the volume of the system changes the partial pressures of the products and reactants and can affect the equilibrium concentrations (see §Effect of change in volume below).

Effect of change in volume Edit

Changing the volume of the system changes the partial pressures of the products and reactants and can affect the equilibrium concentrations. With a pressure increase due to a decrease in volume, the side of the equilibrium with fewer moles is more favorable [6] and with a pressure decrease due to an increase in volume, the side with more moles is more favorable. There is no effect on a reaction where the number of moles of gas is the same on each side of the chemical equation.

Considering the reaction of nitrogen gas with hydrogen gas to form ammonia:

N2 + 3 H2 4 moles ⇌ 2 NH3 2 moles ΔH = -92kJ mol −1

Note the number of moles of gas on the left-hand side and the number of moles of gas on the right-hand side. When the volume of the system is changed, the partial pressures of the gases change. If we were to decrease pressure by increasing volume, the equilibrium of the above reaction will shift to the left, because the reactant side has a greater number of moles than does the product side. The system tries to counteract the decrease in partial pressure of gas molecules by shifting to the side that exerts greater pressure. Similarly, if we were to increase pressure by decreasing volume, the equilibrium shifts to the right, counteracting the pressure increase by shifting to the side with fewer moles of gas that exert less pressure. If the volume is increased because there are more moles of gas on the reactant side, this change is more significant in the denominator of the equilibrium constant expression, causing a shift in equilibrium.

Effect of adding an inert gas Edit

Effect of a catalyst Edit

A catalyst increases the rate of a reaction without being consumed in the reaction. The use of a catalyst does not affect the position and composition of the equilibrium of a reaction, because both the forward and backward reactions are sped up by the same factor.

For example, consider the Haber process for the synthesis of ammonia (NH3):

In the above reaction, iron (Fe) and molybdenum (Mo) will function as catalysts if present. They will accelerate any reactions, but they do not affect the state of the equilibrium.

Le Chatelier's principle refers to states of thermodynamic equilibrium. The latter are stable against perturbations that satisfy certain criteria this is essential to the definition of thermodynamic equilibrium.

It states that changes in the temperature, pressure, volume, or concentration of a system will result in predictable and opposing changes in the system in order to achieve a new equilibrium state.

For this, a state of thermodynamic equilibrium is most conveniently described through a fundamental relation that specifies a cardinal function of state, of the energy kind, or of the entropy kind, as a function of state variables chosen to fit the thermodynamic operations through which a perturbation is to be applied. [7] [8] [9]

In theory and, nearly, in some practical scenarios, a body can be in a stationary state with zero macroscopic flows and rates of chemical reaction (for example, when no suitable catalyst is present), yet not in thermodynamic equilibrium, because it is metastable or unstable then Le Chatelier's principle does not necessarily apply.

A body can also be in a stationary state with non-zero rates of flow and chemical reaction sometimes the word "equilibrium" is used in reference to such states, though by definition they are not thermodynamic equilibria. Sometimes, it is proposed to consider Le Chatelier's principle for such states. For this exercise, rates of flow and of chemical reaction must be considered. Such rates are not supplied by equilibrium thermodynamics. For such states, it has turned out to be difficult or unfeasible to make valid and very general statements that echo Le Chatelier's principle. [10] Prigogine and Defay demonstrate that such a scenario may or may not exhibit moderation, depending upon exactly what conditions are imposed after the perturbation. [11]

In economics, a similar concept also named after Le Chatelier was introduced by American economist Paul Samuelson in 1947. There the generalized Le Chatelier principle is for a maximum condition of economic equilibrium: Where all unknowns of a function are independently variable, auxiliary constraints—"just-binding" in leaving initial equilibrium unchanged—reduce the response to a parameter change. Thus, factor-demand and commodity-supply elasticities are hypothesized to be lower in the short run than in the long run because of the fixed-cost constraint in the short run. [12]

Since the change of the value of an objective function in a neighbourhood of the maximum position is described by the envelope theorem, Le Chatelier's principle can be shown to be a corollary thereof. [13]


15.8: The Effect of a Concentration Change on Equilibrium

If more (Fe^<3+>) is added to the reaction, what will happen?

According to Le Chatelier's Principle, the system will react to minimize the stress. Since Fe 3+ is on the reactant side of this reaction, the rate of the forward reaction will increase in order to "use up" the additional reactant. This will cause the equilibrium to shift to the right, producing more FeSCN 2+ . For this particular reaction, we will be able to see that this has happened, as the solution will become a darker red color.

There are a few different ways to state what happens here when more Fe 3+ is added, all of which have the same meaning:

  • equilibrium shifts to the right
  • equilibrium shifts to the product side
  • the forward reaction is favored

What changes does this cause in the concentrations of the reaction participants?

Equilibrium will shift to the right, which will use up the reactants. The concentration of (ce(aq)>) will decrease (ce<[SCN]^<->: downarrow>) as the rate of the forward reaction increases.

How about the value of K eq ? Notice that the concentration of some reaction participants have increased, while others have decreased. Once equilibrium has re-established itself, the value of K eq will be unchanged.

The value of Keq does not change when changes in concentration cause a shift in equilibrium.

What if more FeSCN 2+ is added?

Again, equilibrium will shift to use up the added substance. In this case, equilibrium will shift to favor the reverse reaction, since the reverse reaction will use up the additional FeSCN 2+ .

  • equilibrium shifts to the left
  • equilibrium shifts to the reactant side
  • the reverse reaction is favored

How do the concentrations of reaction participants change?

(ce>) (ce<[Fe]^<3+>: uparrow>) as the reverse reaction is favored
(ce(aq)>) (ce<[SCN]^<->: uparrow>) as the reverse reaction is favored
(ce>) (ce<[FeSCN]^<2+>> uparrow ) because this is the substance that was added

Concentration can also be changed by removing a substance from the reaction. This is often accomplished by adding another substance that reacts (in a side reaction) with something already in the reaction.

Let's remove SCN - from the system (perhaps by adding some Pb 2+ ions&mdashthe lead(II) ions will form a precipitate with SCN - , removing them from the solution). What will happen now? Equilibrium will shift to replace SCN - &mdashthe reverse reaction will be favored because that is the direction that produces more SCN - .


Change in synthesis rate of a molecule changes equilibrium concentration - Biology

Chemical equilibrium, it is simply defined as a reaction occurring at equal rates in its forward and reverse directions, so that the concentrations of the reacting substances do not change with time. It describes the characteristic of maintaining a balance of reactions, and can be applied to varying mediums, many of which are chemical reactions. One such example of chemical equilibrium that is representative in real life is the production of methanol through the combination of both Hydrogen atoms and Carbon Monoxide molecules.

The synthesis reaction can be represented by the equation:

Were all species are in a gaseous state,

In the synthesis of of methanol, large amounts of hydrogen and carbon monoxide are combined at high temperatures and pressures to create the product of methanol. It is immediately noticeable that the equation confers to a homogeneous equilibrium where all species are in the same state. It can also be noted that this reaction is quite simple when compared to Le Chatelier’s Principles. For example there are 3 methods of disturbing this system at equilibrium:

Changing Concentration:

When a certain concentration is increased or decreased, the rate of change will remain constant but the overall equilibrium will be shifted in the corresponding direction,

(When the concentrations of reactants are increased, the equilibrium shifts right to accommodate for the change and creates more products, in relation if the concentration of the reactants is decreased the equilibrium will shift left to utilize less reactants )

(When the concentrations of products are increased, the equilibrium shifts left to accommodate for the change and utilizes more reactants, in relation if the concentration of the products is decreased the equilibrium will shift right to create more products )

Changing Temperature:

Temperature has a major role in the production of Methanol, through the combination of Hydrogen and Carbon Monoxide, the synthesis itself can only occur when high heat an pressure are present. But with varying levels of temperature the concentrations of either the reactants or products can change. For example:

When heat is added to the reaction, the equilibrium shifts right and more product is produced as a result, in relation when temperature is decreased, the equilibrium shifts left and more reactant is created.

Changing Pressure:

Pressure also has an important role on the equilibrium of this equation, pressure is constantly measured and adjusted so that the equilibrium will be optimized to produce the most product. But with varying levels of pressure the concentrations of either the reactants or products can change. For example:

If the pressure is increased the equilibrium will shift to the right, the side with the fewest moles and create more product, while if there was a decrease in pressure the equilibrium would shift left, to the side with the most moles, creating more reactants.

Now that the main factors affecting the equilibrium are known, the reasons behind why such a disturbance would occur can be explained. throughout the synthesis of methanol, many safety precautions must be adhered many of which include safe operating temperatures and pressures. this is important to note because it allows for technicians to both optimize (in this case increase) both the temperature and pressure to help shift the equilibrium and as a result produce the most product (Methanol) in the safest environment. The maximum temperature allowed during the synthesis is roughly 400 degrees Celsius, while the maximum pressure allowed is around 300 ATM. this is helpful in many ways, since the reaction is optimized a large sum of product will be created which will continue to supply the demand for it.

Helpful Websites:

This website will go into more detail about the procedures of using this equilibrium and how the maximum yield is achieved:

This website will explain the different methods of obtaining methanol and different ways of using its equilibrium:


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