STPM Chemistry Term 1 Topic 5 Reaction Kinetics

11/$o\m-3

L '.i\ ' i'''l-'

LJ r r.u\dv,.-3€ ig,flX#. h exa|/l

Topic5: ReactionKinetics

-JIAI E

Cowntrattbn

Rate of a reactionis the changeof the

dforoduc0 dt

=

Rate = -

molJrrd S-l : .rrut"i.qk . perunittime. of a reactant or a product

no\ Arvi3

ln For reaction : aA +

bB

)

rr\,re arb,tor,.dA.s ''^ Rate of disappearanceof reactants= (Ytd.latts -ve).

cC +

';"$rt ,t Nr:{nollm3s-l lCo,uorl

"\D

slo]c\toyrre*rtcCoe,0ftc]ertL .

= 4[o] A a ,.- Gl 4il

= Rateof appearance / formation of products

H

".

= A#

JtA] -= --+ atBI=-rZ at4-+ --w'T Ear^U R a t e =- :q b ;T-

E cEtt, *t*t A[il*.q\*,*ro6

N1t34t ) lNH3,

E n) '*,*n 4 oh.^yp.oante "t-

f *Nl.\3._ lF^"\';+ -

a-rnr:=-38 - l, n}1il =-l {rHrJ='-;;I o"- = A| -df^'lJ-+ 4ENr43'1 -dE. lt",t- . -{=z |

4 Nl43=qfo^F"*n {ormckton

l*t( + .fo.rnahon Nq=1'1too\ drnf s-f . "$ 't -S C ) , "Pp-tarue l. fn the reaction: HzOz+ 2l- + 2H' ) 2H2O * lz ''t-i;d;;rorm-"ti* oi f, i"zr iot roiort s-i,oetermin-e'fne rateofformation ofwater a 'L l [ tn4>v r o) 1 n ,l ,tr Jo[ f iLl l' 4 0 rl o j ra )l L 1 , . d , ^l tOd) -..nr3) dLtl L ") 1 .,:-dtW ol,tl't"o]

L'T=-Ei'.

T

l/,1.,,^_. :4x(O*nol alla-\g-t

.nstarfuansralz at t--o . _ /_ &_+?g_:_

lnrt;nporlorrgS (ii) instantaneous rate

(i) average rate

= chanqein I I time taken

= gradientof tangentat a particular time

(iii) initial initialrate rate

= rateat timezero = gradientof tangentat t = 0 0.016

M | /': il*

W'W

0.0t{ 0.0t?

t':ojl.

03t0

nr/rjri

0.06

(rHiw17c

0.006 0.001 0.@ 0

Time

I

) pudtcl5

oaacbrrts :

dun'ra'j

rdr,rcts A + B_+p$rtucts A + A * A -"----+Fr+0s,

6

i :'f L i/ --.1

i^l

/'Pt

{-

c.l

I

lrtilnti rrre

c,j

?

11

rq.{a.

'1.

' k Inl^ fg]" I l0,l-\nr,.;;1n

rt vnI w, Y"

-ox\3 , , tt t

,ttl

(j, t:j

.f "t-rL l , i. Jl,

I

^ ,1,.(/\rl

iJ l.|,{,

, ,.rc l,;,r], r,'ii -'kf Al

/i

t,?

t

fl ( ( 1"{l'^'tff /

S'.1| i,trf

r:

; t

lrl

---

( rxo

L

i.t

delurvtirti nlsE

ta{6 = k-f AJ* tgJ "

' k[AJ'[sJ'

-i

- I

"!

)

m:l'n-. I d.rt to tto\et*\o;15

(t

rn ratr d*ov*^*1frf I

-.

lh

t cr vUt j^l :\ / ^ (.!7r '{f, j

I

J

oil - _:,

.l

lC\,"'icl

'

,'1. t,';,; - f:r f

i.,l

' I

r ( .r t i

ri,

':r

.,

t,f

t-

-:rh i

ra{e: k llurt ."i. CB,l t = k I t( d 3 t r . g g r J t

I

\r

l-, t'! a

ior-J" rn=l ll:o

I

.t," y'- 1 r-, 5

, ,; t:: l. Cttlr,t f,' "t t

- , .r

\-

.;

-.

':!-

. , ( : . i t . ) 1O L I ')

'

/ r., zym(6,4)n

:k

t

i:; !1';1 ,

i:::tt

A8 1. Thefollowfng reaction occursat ?FoC.?j.W+2W 1

€g=

C 2tlaofl +

WD

"Bteojj@ 4 . 0x 1 0

Et

3.2x 10 1 . 6x 1 0

'jotJ =o[,ro)"(

?e,= 9?'

8 . 0x 1 0

\--I a)

1 . 2 8x 1 0

Describe theorderfor-rp#n *fu. r"nO ,a+e= kffhl'[ il"o]'

to fi}st Jn" '6nfra "erPct A x setod, "'de,v u"*h reApct{o B . \

b) calculatethe raleconslanr.ry-The-reac(;ton . , .i , . , , 4 , 0 x t o - + =k ( o , r 0 f i o , i ; 1 t ;.= o,tF..rra { o l-> c) Writetheraleequarron. ) ^6rvrirt

.ate-_o,+ t N"-jI Hrolt

d) Cafculate the ratefor Trial5 .lJxto-3aa 6!pla'3,y1s;t m{p = O,t;-(0,30)(O,th)a= e) Cafcutate rheconcen-*:il4fven

thedaratromTriat6.

/,28xro-).-o,*LlU.I[o,y)-

,

A;.3 [N"J = p,).mo\

lL,ld^s

k = 62.1M'1s-1fora reaction which issecond order ::1il,:r;"jt:,Tsfant reaction forreactant A, (M/sec) wr,"n in" iniii"r .on.il;ff; A is0.0050 M. ra{e. k r;lr!" = s),1fi,ooSo;> --

o.

/.55''o; I )rr,'3 s-l 2 Mnoa'+s Hzczo4+ 6 H*-+ z rilnz*+ 10co2 + g Hzo

* c,o,-PI, ouP51" J:P :""=u.rrr,H$=ffi

10 :Lt Lq:-il*l*r i-1-0**-IL--1,0 exlo il ..3I1*0:_""."i1 -rxro "1,.{+_ li*" jL__=9J-19:

#wlffir=ffi 1 . 2x 1 0

4

letftr {''

af,*,'

.t =)A A=).

"_".,

((,o)' ? .: t,bxtoB k(rxrar)A1t*to9)o

3 . 5x 1 0

7

(1rrtrry( otL Txto+T(I x{.-r)-A

reaoaq! .,, _ ?^"^t',P?t!ilg"t"g7,.h =ze'rc'fficrA =)B 9 B=r

,,^'tiiih;,H;K _un rqfs.=kf u"o*]"lurtrd / c) calcutate therarelor Trial5. rxto-l ) k(rxro-3)'( 7ru\ \, f,6xr0-3= k = ) X(OS *ot-'A*''r-, t'

R

$,,## =xil","'ttti:*[:;* | = )c

_.r..-

ll}'htrd1 t*.^t5, = i"-,.01(1'rxro rqte.tc* t , or

7

(^uto*-s -, ;3 , -t ,^,iJr1^9 ^

eSlattn R red'rct;on' awrAo4ox

Exercise:

1.Aqueouschlorine dioxidedisproportionates in an alkalinesolutionaccording to the +3 following +b equation. -r ,.29loz(aq)+ zoH-(aq) 9lo3-(aq)+ cloi(aq) + Hzo(l) (af+ Basedontheaboveequatiorfexplainwhatdo youunderstand by thetermdrcproportionation.l2l

is a reacton *6efu Disproporttonctton "I """ """"3'

"""I"

iit

6artz ubstaltcz w&"qool o).tJdtm ud

(b) Theresultsof thekineticstudyof thedisproportionation of aqueouschloridedioxideareshownin thetable below.

-xperiment number 1

0.0575

tOH-l/moldm-3 0.0216

2

0.0713

0.0216

[ClO2/moldm-3

Initialrate/moldm-3s-1 1.26x 1O-2

8.21x 10-3

3 0.0575 0.0333 1.26x 1O-2 (i)DeterminetheorderofreactionfoitheoiEroportonationotJ,..'s.t

, j D I l , r t x t o - )k=( 0 , 0 1 1 3 ) " { 0 o t ' 6 1 n *Df 8.I x(o*=k (g,ohi)il(o,orb)^

- F izp :ig;ff), *=i:fi;i:

, u . q -3/ , , , , - 1 rate=kfcttl"l1 [orf'I' /,fl yto3" k ( 0"0qfi)"( 0,0>lb)

;.ri= ril,q(i rif^,,rri),t,ri

(ii)Calculate rateconstant, k, for thedisproportionation of aqueouschlorinedioxide.

ll r9 : htqrq:l: t_ot k: 1/ktyt-'ol,n! S' s.xIl:" : tr\!:q+jlll.qryl) .rqoiJ

(iii)Calculate thepH of theaqueouschlorinedioxideif itsconcentration is 0.100moldm-3andthe initialrateof -['5,0 foHl* x 10-2motdm-3s-1. Grrvg11 l*disproportio-nationis3.56 plt= IOH , f oH =

rata : ktsqJ[oH:J, : {{l(9:19?)l[9t'],'p{!/: l:nrr(o-1911?) ' ?:??t!q-] : 11 = z ior,rf;:0,0i,0 ,iil,n-poH "' r" '" /)rfq rj,F ;ih; ;;;;;;itif'

iiiil;ffi

"i

ru,o, i;i; No;;;;o;;i 3ili i;;;;

;Jffi.

l^[Aft =-kt +ln[Al"

/rlN.ry

Fromthe graph , for the O""o.porition of N2O5, (i) determinethe order of reaction, F

nr$

o.def

g

(ii) calculatethe rate constant,

=l.bllto{ s-t

mt1 con:tonlc, k :-ffiA tttL = (iii)calculatethe half-life,

*y

t_-o$+i=h\bs

- lnL

t>

Kt

(iv) writethe rate equation

sJ rcra=l,ii *touI N"o

3a) ln acid solution,bromideions are slowlyoxidisedto brominey'by bromate(V)ions as representedby the following ionicequation. BrOs- + 6H'+ sBi ) 3Br2 + 3HzO ExperimentNumber

[BrOj ]/ moldm

[Bf ]/moldm

lnitialrateof reaction/mol dm-"s-'

[H- ]/moldm

0.400 0.280 0.031 0.031 0.600 0.280 0.600 0.031 0.560 4 0.400 0.062 0.280 The followingdatagivesthe.regiglt temperature. the of fourexperiments at constant i) Writetheivo naft-Stt"atonsfor theabovereaction.

1 . 2 9x 1 0 1 . 9 4x 1 0

1

2 3

I B'

- -+

B"r * )e-

3 . 8 7x 1 0 5 . 1 6x 1 0"

toxtAatron)/

--r !*:9 * 9: I Z rlllrl9:9r-:!9: kr&0s-1":!:::l:H:]: nn\e= ffi#: ffi :ltst)(Bffi)ll;3*): 't',q+xt0*":'f'D:6uo'\iif """""""* ezt4t$f",

ii) Calculatethe orderof reactionwith respectto BrO3-. , Bf. and. H* , f5ns.

/'r4:!......!:)1 I19.1 ...1 "....9.?!f

l:bgtI 15' M\",I'

ffiffi'j:ffi:(ffi1 ns I

.. . ^

p =).

:: 1::::1T:: J*d/,wr Tb'*;-

to-eOs

;tV d/;J-n;

&:

Thi;;;F Nr!;*'";;1 :.,Y

4(b) Peroxyacetylnitrate(PAN) is an air pollutantformedin the photochemicalsmog"The concentrationof PAN in a pollutedair a sampleis fs analysed anafvsedat 25oC The resultsare olven In lhetable below atZ5-CJ.

Time/min

0

Concentration of PAN/10-10moldm-3

8.4

1 0 . 0 20.0 6.6

5.3

30.0

40.0

50.0 60.0

4.2

3.5

2.8

2,'l

q

(i)

't PA}d/l'o't r"{ }tn-3 1,x616p{vAtron

Deterriinegraphically of PAN atZSoC.111 the orderof the decomposition

'0.0 3'0o 4b,o V'0,0 bb,O

s l\r Q.stI'atT-L€-t. 3o"D

-30,0=30"&. T; i,;J il( f,Qts 5,9"9 (ii)

Eo'* ;s Cot ."der reaeheq,

Calculatethe-1ateconstantfor the decomposition of PAN atZSoC. IZI l, -- Q$41 lv +'t^ .t.7.....

k:'S:qoF\!h:l (iii) Predictthe concentrationof PAN in air at 25oC after 90 minutes. [2] rh rI r , ^\ ": 3 1rto"o)=/o ;t.M;;ii fftp+^f"" rd,]; ; ll_{:'iJ_ll rytd*: \ . . . .ll. . 1tt'. I . : . . . . . . . . . . . . . . . . . m o 5(b) (i) The mechanismof the decompositionof ozonein the stratosphereis proposedto occurvia two stepsas follows: t03#oz+o step 1 ( fast)

o *

oj

k',

2oz

steP2(slow)

wherek1,k -1andk2 arethe rateconstants for thereactions. Writetheequation for theoverallreaction, andderivethe rateequation for thedecomposition of ozone.[6]

: ti*filg,fillffn*::i

4 o?oila ::dj "$**--+.:1f*@osrftc'1

r0

^ /'t$

Y\

A-t

$* . Pt-Y{ O.(c) Cycnlhpanedecomposes intoprc'pene throughtheringopeningof cyclopropane according to theequation CsHo ) CH2=611611. The rateconstant forthedecomposition is 15.12s-l at 400oc. (i) Write the rateequationfor the decompositionof cyclopropane.

= tb,nt CrUrJ* / rc,.{a (ii) Calculatethe half-lifeof cyclpropane.

t'' *r,'

t11

"/ o.o+bgs ffi= e+O,q$

*.

(iii) lf 1.0 mol of cyclopropaneis introducedinto a 1 dm3container,what is the concentrationof cyclopropaneat 4OOoC

lr[gruJ +h(l:9) q,oulglt) : _!lb:t])(

(iv)Whatis therelationship betweencyclopropane andpropene? t1l thal qrQ t5ofne,1,5 ......d.

(v) Namea chemical compound, otherthancyclopropane, thatmaybe usedto producepropene t1l

ri*s*:t

ilo?af0\ "'

""1""1""

o{- a\cohor)

-"1. Propanone,CHaCOCH3, re?ctSwith brominein acidicsolutionaccordingto the equation H' CH3COCH3a Brz + HBr ---) CH3COCH2BT A seriesof experimentswere carriedout to studythe rate of reactionbetweenCH3COCH3and Br2at room temperatureTheresuIts of the experimentsare shown in the tablebelow. Expeiment / Initialrate/ lcH3cocH3l [BrzJl ^ lHcrl/^ number mol dm" moldm' mol dm" mol dm{ s-l 1 0.80 0.0010 0.20 3.4 x 10-" 2 0.80 0.0020 o.2a 3.4 x 10-3 ? 1.60 0.0010 0.20 6.8 x 10-3 4 0.80 0.0010 0.40 6.8 x 10-3 (a) Determinethe rate law for the reactionbetwepnCH3COCH3and Brr. t8l

c( _ klusnupl^[+,1^[uufP4 ffi

, #XlS:GHft,

rcNs * rvLw\3ruLvr-3j L->J L".-".:J..:...t.....e...w.!.r.r.|.....?FJE=:..;.\@.1..v, "irFdi;tm3'-' 'U;8 ; lF= )n r : ti!+tF ( *Sf; slq-4me,.t -1*l tL=J

/ A > D. t / 1

./

\

ffiffiiIffiff.:tffi):ttsH):z i .'o.'E(f) ;""'

"""'r

4;i _; ??)4 I2l =-h[q111ao a,tr1 rc!uEael7 ::k : p,q il n:!-i4r1l- i '1.........'...

(b) tD)

Calculate ualcurate therate tne rateconstant, constant, k, lor K, for the the reaction. reaction.

3,4xro*. k [o.so)( o.>o) (c)

Explainthe roleof HCI in the reaction. .

t3I

)114.q L|L[prcv,.J^i|+,,^^|;/i:A*tJ(,;;+,o.a$i+1;;;;,'!:1t5,/; . . { . .... .. . .

i;i {:r"{trffi,k#:^4,t,Sh*in/rzt

(a,ioit,,l tl

(iii)writetherateequation for thereaction[1]

r - . . -1 )-

-h

r*z =,F#

117t20141

lCaHrl

11. (a) Explainthe termsrateequation,orderof reactionand rateconstant.

: k\,, l1ddtron :L..q^..fl6t91 $ra| dlgd: *hg t1lar@ t1 ^155f1 ' "t .eqd\rrqctqrrt' ^ i o s\ Oder

,-+ '\\e reacttm ca+?on

reactrm i$S\ to a ;saetanrf ;; . .*\; ' . " " rerpac{. . ' . .p;"; ..t.. ""1'..'

;"

-*1..go,"^

"fJ

.*;^i; i*;tTH.;T:',.*,.';*;t-::#:* o"; ;; :q.^r.

(b)Ethylethanoate undergoes a stowacio-catarvluotnvoroivrir i."*"i". dl!#ft :^ -thz CH3CO?C2H' + HrO

HCt

100 125

"?:y

a l td the followino results were obtainecl

0.200 0.152 0 . 11 5 0.088 0.067 0.051

75

+(^+

I CH3CO?H + C?H'OH

The reactionwas followedtwicewith differentconcentrations S of HC Time/ min. With[HCl]=0.1 moldm-' lethylethanoatel/ mol dm-3

0 25 50

+ ;;;.+;i[f

r-o\*'!

With IHC|]= 0.2 moldm-" lethylethanoatel/ mol dm-3

0.200 0.115

0.067 0.038 0.022 0.013

L*fl,{gf0. b IlbJ166t}i3

*,rJJ glil\-l

(ii)Useyourgraphs 1. to showthatthereactionis firstorderwithrespectto theesrer,

Jr l"$ qet;g,dfo lgtf !fu, lf s {,* q4oo)(0 , ! ) bgO"'o-3 k = 0,1)b,ntol-'alms mirfl (c) Why is it not possibleto determinethe orderwith respectio waterin thisexperiment?

'fo

rema)n

for

r-tctetion,

Plottheexperimental resultson the

-.ii) Explain,as fully as you can, why the experimentalresultsindicatethat the overallkineticsare first crd.er..

t\q+q..Jc'ta\ vdqrg OQ ,4t..*rlg. srnrs c'nl ut ,4".*!.b rbr.*jrd,H.r,.Jtlfiinph "t

*M+:#ws*Fsd#"[,!=rfi{iiTl,#f i;i,,wl#lffi,*r,I*reffi -+e...qre1!3,'I;tpn F+hqnpl .'S.. used.inle.,q?,..q.(eal fhsit:

.nT.e$e.lgl .rgn{$...3p?ID.!:M?t

(c)(i)Calculate howmanymoleYofgaswereproduced in theexperiment, conducted at roomiemperature and 3*3ff*pressure.

q:o0pc^l.,Ng."$.',nde...*Az=#*l.:?:t!.r.I.?".3&.rc!g'

j c\ r o ** ** jf:,} ^[fffi;'J","*':;:.:^*;?iffiiflHffi'ffiti ric,li-*,r, (d)Thestudent wishesto modifytheexperiment bychanging theconcentration of theethanol. (i)Explain, withtheaidof an equation, whywatershouldnotbe usedto dilutetheethanol.

"'"'.'u

-'NJ MrQ+ .Neol J fl*

i l:{t*g oat*lggf+.tt_^th u,atl o 8.n h*"-"St5^ (ii)Suggesta suitablesolventthe studentcoulduseto dilutethe ethanol. \enzsro

t+

*o\er

"t$

6qqettorr

dotentined b5 StoithiolrnrG*a

;*fi$,*,8.r1

Forn stJctF sdqgaat M€cJ^a{srn '-..,0rli'1'rqt) (i) reaction mecnGnism is thesequernce cf .#UlUTi rilrEril,cily lreps steps tW

to re ueUUilOe describe ihelgfmallon ine formation pJ OI fifeoUCIS. andis pi.oposed An( Rrqducts, step)

basedon rcte equation( vrhichconteinsonly the speciesihat are involvedin the r*te:- detera^tn;a (ii) the rate- determiningstep is the siep with the highestactivationenergyor tne stoweststep stepsmustgivethe overallbalancedstoiChiometric equation {iii)the surnof ali the individual (i) by order of reaction Orderof reaction

I

Molecularity ( the no. of species involvedin rate deiermining step)

I Rate determining step

!f order o

lf orderof the reactionr. stoichiomelry;t reaction, .t < - reaction occursin morethan1 step

reaction, 1 - reaction occuronlyin onestep - eg.rate= k [RCH2Br][OHl

e.g:rate=k[(CH3[CBr]

--+ RCll>B.t ol.t RCilzOH r B.-

-* (tLl)aLB, * 0H-+(tHr)rco tB." elucrrton

Mechanism:

Mechanism:

+

B'' I fcrr.\t+ i; aiHr)S& + : oH'+ BrR(,,lrOH RLI{&+ $?t "t ' sT", [M)t.noH'S'(cu.1rcoH

*

Mechanism

Stepsto write mechanism:

S#f*mfroffssd nmsfr rnlsrrs

1) check whether order cf reaction

' iilethnltm rocornf HUsf lwovenff sfolcfiltrfdry afnid,ofiffderyerfnonhflf #hmrlrpd ftate lru , fttfl?thry fltl$Iadd stfpJ rplorrenflfshnmd ryr#on

-|JlF

stoichio-

co#mrg lsrnttrdy due hgchtrtysdortwhfan CIgssr# tarroruJ

metry

1P*9 .{ryryr,il{*jfhn, ldeclnnlsm fftlSlco#etafe rfltrfiahkry

l write the overall balanced equation

f*te,ltiv;'$qfi

It

3) write the ratedetermining step ( it

mustbe the same as crder of reactionl rate law)

S{*p ? i

rafe determining

@ Frop'

arodrct,

't"""""'

hVp)yq .b,nilg-, .J:.n .?eto. *7*r *.fh *p ec*

to brom,'ng.$

concerrtcaton

"(

B.. do.s ^ot

....tl't s.t.+lt...-t*. d .q"*91:.. -- -SOs. _;b)Oxidesof nitrogenin the atmospherecontributeto the formationof acid rain by catalysingthe olidationof SO2to Write equationsto show how this occurs,and describethe type of catalysisobservedhere. 250' t Or -> :S03.

re a.stiYation

enerlgy

raE csnstant \Y

J

\* :

k

?

racbr

fiequsrcy pre-exp(]nenjal

t*k:rs-rA-Ea

Agl\/ I

lC*

t\

-

fa:br

Mn ErnPeratrre

grrqcr:nsa'rt s3\ Jrnol-' K-\ .

-tf

^

/nK=-F(7)+lnf\ ""'. Kt',

Ff-r-

* : rosrA - =:===*--

V N

-==-*e

\ mathEmaticaj quantity. e F rr

(or

;

-Ea RT -kel

'^t .1 t--qo'*: >*/r-' | t-1. ,

fa

'}l.^ l n, kat

Uses of Arrhenius Effect of T & catalyst on rate constant, k 1. Whentemperature increases, 2 Catalystlowersthe activaiionenergy. k incf€dSes rate imr?ases So, k lncreaEeS -, rate ----$g!ggsl

1

23O

21O

Rcte -nsf-ard-,k , on\ @

25C

qr T a.,.J ."t-!s* tt

.\,\

r

(b) Determination of activationenergy (i) Formulamethod

[nk2

:

[nk1

__t

\tN

1l Tr)

kr

,,4,'

.l^ ---{ ,

{ R = 8.31J mol-1Kr

L,

Eg. In a reaction,rateconstantsare 2.3 x 10-3s-l and 4.3 x 10'2s-l at 2OoCand 90oCrespectively. What is the activationenergyof the reaction?

+\l hY. - Br+ fi\Tr-T,

"'kr

r-\ t - l t g r d , 3 ) =-- F o t r a(-ffiffi /' frl f r*+r,3) ,t*tt6/ F o = 3 6 q 1 3 , bl

=36.q14kf x 31tJ.^"\-\ To determinethe rateconstantat certaintemperature

7'

Ea

k"

eg. In a reaction,the activationenergyis 275 kJ mofl. The rate constantat 400oCis 1.16x 10{ s-1.What is the rate constantat 450oC? hIt Eqr r .It , kt

1"4 =- R-(T, - T,)

-^*__*rr) /h(,qS ), - #= (o*-*r, rr{z oons*ar* *f 4b0'C, kr = 3,48 tlo*

a-r

(ii) GraphicalMethod:

-Ea. 1 RT

lnk-lnA+ Y=

b

+

|TIX

Make a plot of In k vs, 1/T Slope = -EalR Ea=-slopexR R - 8-314 J/K-mcl

Ea= -{-12247)x8_314 = 1 A 2 , O O OJ = 1O2 kJ

tQ tL)

txerctSe: 1 { b ) T h e a c t i v a t ieonne r g yE, , , o f a r e a c t i o n c abne c a l c u l a t e d f r otrhne A r r h e n i u s e q u a t iko=n A e - E d : l r , w h e r e r < = rateconstant,R = gasconstant,T =temperatura, A = frequencyfactor, ln an investigation, the rateconstantsfor the gas-phasedecomposition of dinitrogenoxideintoits elamentsare (Q5b/2005) measuredat fivedifferenttemoeratures.The resultsare shournin the table ln kls-' T/K -3 838 1.10x10-'*h /' lq'rlo-5 -' -C ?ql xto 1001 3 . 8 0x 1 0 -' -0 *ro-+ Q'11 I UJU E . 7 ' xl 1 0 r3, 8 {.bo rto 1053 1 . 6 7 0 . st3 -+ 8.S1xro 9.+.1 1125 11.5 graphically Determine the activation energyof the decomposition of dinitrogen oxide. Writean equationfor the and statathe orderof thisreaction. t8l

+ lk'.

6s

tnh" tnA- F(+).

I

6

-7

-q

-b

-? ll.lr0 -+ lNz * 0' ae"rl

on unrt.rPK | '+v. rta&on

: #*:dr

^fft h N,0.

2. At 45'C and 70oC, the first order rate constantsof a reactionare 1.79x is the enthalpyof activation? [ R = 8.31J mol-lKl1

rot6 ,.0 +.15;io;;ti ;;;p".ii""rv. ffi"l

t\

ro{r13/

Ea = tll l t+15 = ll1k5 ^ol'' 3.il; ffi;;i;.';q;"ii"' i" gi";; [ :o;'e;'ii.A;"il;; n"pJ""'i7til;; i;;l;; ;l s;"cil;; ;irt;b "' Calculatethe activation enerjy, in kJ.mol-l, for thisreaction. [GasconstantR = 8.31J Kt mol-1] l16t2}O4l

{r(=t: - Fft("im-r-"1) Eq

: 818>1 J

= 81,5 k5 . ^ot-t tQ

!l

4 Variationof ihe rateconstanlwithtemperature fcrthe reactionA )

T

Temoerature iK x 298 3,35 )-r 308 3.!ts ro€ 318 3,r+x D : 3 3,oB to-3 32A

a R b b-3

28 + c it 5

Rateconstant/s-' 1 . 7 4x 1 0 b 6.61x 10-' 2 . 5 1x 1 0 7 . 5 9x 1 0 *

2 . 4 0x 1 0 "

338

(a)(i)Whatis meantby rateconstant? [1]

tabre berow T"?;Un" -t0,qs -q.L)

-s.>1 -'1,E

- 6 ,o 3 .

qqnp*qntgS .qry_pqdlflqlrtV &trlgen+hereqcf,sr rctta otd fiiz ..tgi(..ctrs€91l{..1)....^.

(ii)What istheorderof thisreaction? Justify;lr.';.;;;

i;fhnae^*J+i;

"+

.eqetonts 'tl.c^+qr€ lii alk'e$stron'

fLe.....ea..{,qn..:1...$$.. Si"s*gder g.7.r.o,r....!...g:' . .gde{..1aifh ..31?g1t..to..A1. .R1te..cD.^.*4.^r. "t (b) (DBy plottinga graphof ln k against1/T, determinethe activationenergyfor the reactionabove. ., ! r hbt__,/l -.., ,

f/x'o-rK

kJ *u\-'

(ii) Basedon the graphwhich you have plofted,calculatethe half-lifeof the abovereactionat 300 K. -l

T= 3ook' =r;;;.;..;;-i

,{= g.?5xro-S +.; -a6q3 ;:;^;

[4]

[19/2015]

.tfi {21- \./

PqctioA'

a*a\tc

p{p,rat s€'$e sarne

qenefiL\ ' honlo heterp artto

-

,t4{€r€fit. ^ 'd$et+ catktgst pvnd..rce

i-occursvrherir:6[|ystandi-occr.lr"sv,,.irgpcat3iystancireecrantl-@uctsof| reactants arein_gd\g--arein-M. phl,sicalstatej I *'" iuu"tion is a catatysiforih;| Physii:alstate. re"ction. i | i transitionelementsare - Transitio.metalsi ccmpouncis (because j zrrrnoor Sceor2_t-16H* I Elg{gggrouscatarvst

il."ffi;ffi,

lt@sin

I

\irc**i1'

e ' g,ffi.::l^,.i 1: 2l-'+szoaz-i

l z + z s , a t i I e .-g :i ' { 3 *'r1l t.^-.--Il tci) ,ir r r^X) tfe3 | t=-.=---Jf.i.-{al I ..it6

trodilct:catalvst

|r = , . a t e i n c r e a s e _s a s c a t a l y s t i s p r o d u c e Ratedecreases' | because

l*dsorption: I'

Fe3*ascaiai*!

-;zco,1-i{r,i-ibH,o

I

zni

H-tt i-r ".csorpi:on: i:I __ia

the

I rate

,^..*Jtt+

|tnt". * Tlwexa ,] rJ'+,[q,r+a" +)F.ot i f inxfu^tr_* *lNtn:"H;:"T[T:i::JffJfiT \={ aFe'* 2s0+1t \0i-+ rF.e*'I cataivel'This i i

I

- t^to"ken thebonds in i (rq,cta themotecutes t) I - -i1g""6e-- theconcentration - - of - I I| i

T I i|

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t

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time |\ rni