answers for energetic questions

8/10/2019 answers for energetic questions

1/122

1. D[1]

2. (a)

(1) for around carbon and its hydrogens

(1) for around oxygen and its hydrogen

Allow all dots or all crossesIgnore circles around atoms 2

(b) (i) C(s) / (graphite) + 2 2(g) + 2!2(g) Correct species (1)

Allow oxygen abo"e arrows rather than in box

#alancing and state symbols (1)

$econd mar% dependent on correct species except as below witheither hydrogen or oxygen or both as atomse&gC(s) / (graphite) + ' (g) + '!(g)

$cores second mar% 2

(ii) nthalpy / energy / heat(energy) change when one mole of asubstance (1)

Is formed from its elements (in their most stable / standard states) (1)

nder standard conditions of 2* ,/ 2- .C / any stated temperatureAND 1 atm pressure / 101 kPa / 100 kPa (1)

Definitions based on lattice enthalpies may score third mark only 3

heat required / heat given out / heat taken in

(iii) c = - 1 + (1)= ( 0 12 -& + 1 * &-) 3 (12 *&4)5 1627 (1)!"nore units

#orrect ans$er alone = marks

+% & = 1

-''0 = 1 if omit multiply by

Sri Lankan School 1


2/122

(c) (i) 0 % 0 288 0 '&4 5 46 8-(&2) (9) ignore sf except 4 sf i&e& 28888

OR

0 % 0 288 0 8&88'4 5 46& 8- (2) ki"nore sf e*cept 1 sf i e 0

i"nore si"nsi"nore mol 14 1

(ii) 0 ' /3 = 0 0 &, (mol)

i"nore sf e*cept 1 sf i e 0 03 1

(iii) 1%30, /0 0 &, = 17- 888 (9 mol 14) (3sf)

OR

17- (%9 mol 14) (3sf)

!"nore missin" units but penalise incorrect units

llo$ . from (c)(i) (ii) 1

(i ) ny t$o from

s heat/ener"y absorbed by apparatus / heat/ener"y :lost; tosurroundings (1)

methanol not completely burnt / incomplete combustion (1)

methanol :lost; by e"aporation (1)cannot ensure all products are at standard conditions at end of reaction / $ater is produced as a "as / reaction not carried outin the standard conditions (1)

just heat/energy loss

just incomplete reaction[14]

3. 2[1]

Sri Lankan School 2


3/122

4. (a) (i) S system = 104 + (& 0 7*&*) 1 ' (1)

= (+)1 , &( mol 14 5 14) / (+)1 & ( mol 14 5 14) (1)

OR

(+) 0 1 & (k mol 14 5 14) (2)!6789 units e en if incorrect

correct ans$er $ith no $orkin" scores

:alue usin" 1 for ; 8 = 147 &* scores 4

se of "alue for 8(") (1 %) "i es

4 ' ( mol 14 5 14) (1)

correct alue $ith incorrect si"n scores 1

185

(ii)


4/122

(i ) (1 , & 12*-&7)5 1 110 (J mo 1 ! 1 )

89

1 0.110 (kJ mo 1 ! 1 )

could use 1 & or 4& etc

. from (a)(i) and (iii)

(")#02.$ (J mo 1 ! 1 ) i% &a 'e %or # 2O( ) *as 'sed in (a) (i)

459.5 (J mol 1 ! 1) i% &a 'e %or one 2O *as 'sed in (a) (i) 1

$ns ers here values in % are added to k%

( ) Decomposition (at 4 5) $ill not occur as $ total is ne"ati e /

9eactions are only spontaneous if total entropy chan"e is positi e /decomposition not thermodynamically feasible / (hydrated cobaltchloride) is thermodynamically stable

. if ans$er to (a)(i ) is positi e sho$in" decomposition (at 4 5)may occur

OR

Positi e total entropy chan"e doesn ;t indicate rate of reaction 4

(b) (i) First mark

.hermometer (1)Second mark (dependent on first)depends on choosin" thermometer

as temperature chan"e is small /(>) error in balance smaller than for temperature readin"(>) error in pipette smaller than for temperature readin"(can be sho$n by calculation) /as scale $ith "reater de"ree of precision needed / scale $ith more"raduations needed (1)&'()*+ any references to :accurate thermometer; 2

(ii) ?se more cobalt chloride / less $ater (1)

.o increase temperature rise (1)

@ark independently

%ust use more reactants

se more co"alt chloride and more ater

repeat e-pt

add a lid or e-tra insulation to "eaker

use distilled ater

Sri Lankan School .


5/122

(c) (i) +,-

9adius (of cation) increases (do$n "roup)89 any t*o alues of radiusA@" + = 0 0% B #a + = 0 100 / Cr + = 0 113 (nm) data may be

sho$n beside the table (1)9adius #o + = 0 0&, nm89 #o + radius smaller than other ions (1)

Data on / R #o + OR data sho$in" increase in radius do$n6roup !! re uired for O of first t$o marks

orce of attraction bet$een ions decreases (as radius of ions increases)/ char"e density of ions decreases / ne"ati e ion can come closer tonucleus of positi e ion (1)

$LL) redict lattice energy 12--8 to ?2*88 (%9 mol 14

) (1)!6789 si"n '

$tomic radii unless ionic radii also given

*adius o! co"alt chloride

0olarising po er decreases

(ii) First mark9eference to enthalpy of hydration (may be in e uation solution= -E + hydration ) (1)

Second markColubility depends on relati e siFe of lattice ener"y and enthalpyof hydration (1)

ird mark/ RColubility more likely if solution is ne"ati e

OR

(!f solution is positi eB) may / $ill dissol e if S total is positi e

$ +03 sol ation instead of hydration 3

Sri Lankan School 5


6/122

(d) +,-

First markird ioniFation ener"y i (er) for @" / @" = %%33 k mol 14B (third

ioniFation ener"y for #o = 3 3 k mol 14) (1)

Second mark(.hird ioniFation ener"y for @" is hi"h) because the electron is bein"remo ed from an inner shell / full shell / p le el / p orbital (1)

OR

7ot compensated by hi"her lattice ener"y for @" 3+ (and so formationof @"#l 3 $ould be hi"hly endothermic) (1)

[20]

. 2[1]

#. [1]

. (a) @"#8 3(s) + ;#l(a ) @ gCl (a ) + ; 8(l) + #8 (")

EE8G @"#8 3(s) + ;+(a ) @ g + (a ) + #8 (") +; 8(l)

ll formulae and balancin" (1)

Ctate symbols 1 mar% independentlyB can be gi"en e"en if eg gClformula incorrect or for ; #8 3(a ) (1)

#8 3 1 (s) + ; +(a ) @ C! (") +; 8(l) (1 mark ma*)

EE8G 1 missin"/incorrect state symbol

(b) ny t$o from

2ubbles (of "as)/ fiFFin"/ effer escence (1)

Colid disappears/ disinte"rates /"ets smaller /dissol es89 @"#8 3 disappears (if "i en as solid in (i)) (1)!6789 clear solution forms

@i*ture "ets $armer/cooler 89 temperature chan"e occurs/ heatchan"e occurs (1)

ar"on dio-ide /gas given o!!

0recipitate !orms 4no 3+ !or g l 2 4s66

%ust exothermic

Sri Lankan School 7


7/122

(c) (i) @oles acid = (( , 0 2/ 4888)) 5 8&8-/8&8-8 / - 0 48 12

!"nore units and sf 1

(ii) @ass @" #8 3 = ((0 0, 0 '& 2)) 5 2&486-/ 2&48 /2&44/2&4 (g)A !E F from (c)(i) and (a)

A !E oles acid 0 '& 2 for F (from (i) (1) (' (1,)) if factor of missin" for . from (a))

!"nore sf e*cept 1 sf !"nore units 1

2 / 2 124g6

(iii) .o ensure all acid reacts/ all acid is used up / to ensure productis neutral/ it (;#l) is neutralised 1

$ll reactants used up 3o ensure reaction is complete4 ithout re!erence to l6 3o ensure yield is high 3oensure magnesium car"onate is in e-cess

(i ) ilter

EE8G centrifu"e/ decant/ pour off / (use) filter paper

!"nore comments about heatin" solution first to concentrate it 1

Sieveollect g l 2 in !ilter paper

se !ilter paper to dry crystals+vaporate

Sri Lankan School 9


8/122


9/122

(ii) HG#! 1 lar"er (than #l-) (1)

so (ion) easier to polarise /distort (1)

EE8G for nd markincreases co alent character / more co alent than @"#l / con ersefor @"#l / description of polarisation instead of the term

!f clearly ionsB allo$ reference to iodine instead of iodide (


10/122

$. (a) llo$ formulae throu"hout instead of names

est A add bromine ($ater) /bromine solution EE8G bromine "as/bromination (1)Res' t A no chan"e $ith he*ane / stays oran"e bro$n/ stays red bro$n/ staysyello$ and"oes colourless $ith he*-1-ene (1) nd mark c on 1st

89

est A add (acidified) potassium man"anate((:!!)) (solution) (1) EE8G potassium perman"anate for potassium man"anate(:!!)Res' t A no chan"e $ith he*ane/stays purpleand"oes colourless / bro$n $ith he*-1-ene (1)

89est 5 add alkaline potassium man"anate((:!!)) (solution) (1)

EE8G potassium perman"anate for potassium man"anate(:!!)Res' t5 no chan"e $ith he*ane/stays purpleIand"oes "reen $ith he*-1-ene (1)

Smokiness o! !lame

@romide&odine

'oes clear

(b) (i)

EE8G Partially or fully displayed as lon" as the t$o ; are trans llo$ bonds $hich "o closer to the ; than to # of alkyl"roups on l h s 1

(ii) HG##=# restricts rotation/ #=# pre ents t$istin" /#=# can ;t rotate/ lac% of free rotation round C5C (so the groups can;t change positionrelati"e to the bond) (1)

;e* 12?ene has different groups on the C at each end of C5C /hex?4?ene has 2 hydrogens on the C at one end of C5C / hex?4?enedoesn;t ha"e different groups on the C at one end of C5C / hex?4?enehas no group which ta%es priority on the C at one end of C5C (1)(ans$er can be considered from either he* 14? ene or hex?2?ene) 2

$lkenes can t rotate Double bond is fixed onds cant rotate

Dou"le "ond is on !irst car"on 4unless !urthere-planation6

Sri Lankan School 1:


11/122

(c) (i) i"nore si"ns(,0 0 '7 0 '&4 ) 5 *74'(9)/ *&74' %9 (if con"erted to %9units must be stated)A !E *748 / *788 /*&74 %9 /*&7 %9 4

45: #2 !" !#1$% & '"(")*%

(ii) 8ne mark each for moles of he*ane ener"y chan"e si"nB unitsB si" fi"s (for ener"y chan"e calculated)

@oles he*ane = 0.326$# = (3 % 0 48 1 ) (1)(4&1'/ 3 % 0 48 1 ) = , '000 / , ' k (1)DH 7 82#00 kJ mo 1 /- &00 000 mol 14 / - & 048 & mol 14 (1)

llo$ . A0.32 in (i) ("i es &1 ,3 )B DH 7 81 kJ mo 1 /-1% 000 mol 14

/-1 %048'

mol 14

0.32 in (i) ("i es 4&%& ) DH 7 82#00 kJ mo 1 /- &00 000 mol 14

/- & 048 & mol 14

Ro'ndin o% mo es to 4 010 3 "i es 2400 kJ mol 1 or81 kJ mo 1

ma* (loses moles mark)

ns$er alone (3)@a* if ne"ati e si"n missin" and/or more than sf or error in units 3

(iii) ny fromA

J eat losses (from calorimeter)/ poor insulation

J Incomplete combustion/burning

J Incomplete transfer of heat/ loss by con"ection

J "aporation of fuel (after weighing)

J eat capacity of calorimeter (not included)/ heat absorbed by calorimeter

J easurements not carried out under standard conditions/ 8 is "asB not li uidB in this e*periment

%ust energy losses(ot all he-ane "urns

Data "ooks give average values

e-ane is impure

uman error

Sri Lankan School 11


12/122

(i ) rror in readin" temperature is less than the effect of i"norin" heatloss etc

EE8G8ther errors are "reater than error in temperature readin" / 9eadin"sare $ithin mar"ins of error/ .he accuracy $ith the thermometer isnot si"nificantly different from other measurement errors / 0 1 .Cis insignificant compared to temperature change / sing 8&4.Cthermometer does not change significant figures in final answer / sing 8&4.C thermometer does not reduce errors 4

sing : 1 +, thermometer gi-es a more precise reading butdoes not impro-e accuracy

(d) (i) 7ickel / 7iinely di ided nickel/ 9aney nickel

EE8G Platinum /Pt Palladium/ Pd 9hodium/ 9h

ccept one of the abo e ans$ers combined $ith a commentsuch as


13/122


14/122


15/122

(b) (i) (2ondin" in 7a#l) 100> ionic

OR

almost completely ionic

OR

no co alent character/( ery) little co alent character 1

.olecule (0)

(ii) +,-

"! has (a de"ree of) co alent character (1)

due to polariFation or distortion (of the anion) (1)

(c) +,-

ny t*o of the follo$in"A

J (outermost) electron further from the nucleus/atoms get bigger/more shells

J (outermost) electron more shielded (by inner shells of e?)

J (force of) attraction between nucleus and (outermost)electron decreases (down the Lroup) OR (outermost)electron held less stron"ly (do$n the 6roup) OR (outermost)electron becomes easier to remo e (do$n the 6roup)

&'()*+ any references to(effecti e) nuclear char"e or more protons

ions get "igger 4do n 'roup6[10]

13. (a) (i) -+*8&2

= 0 0,(00) (mol)

correct ans$er only (1) 1

(ii) 00 0 '&4 0 $.2= ' &,, ( ) OR ' &,, k (1)

for correct 3 (1)

&'()*+ sf &'()*+ si"ns at this sta"e



16/122


17/122

(c) (i) nthalpy / ener"y / heat (ener"y) chan"e($hen)one mole of a substance/one mole of a compound (1)

is formed from its elements (in their most stable states) (1)

4 5 / , .C / a stated temperature AND 1 atm pressure/100 kPa (1)&'()*+ any references to concentration 3

energy re uired

OR

energy released

one mole of product(s)

is !ormed !rom its reactants

room temperature/rtp

(ii) #ycle or formula e*pression

Nf = 1 1

= ( 0 1 *') + (2 0 1 2 7) 1 (1 68)

5 490 (k mol 14)J correct expression or cycle (1)

J e"idence for doubling >otN

c J#Kand N

c J; K(1)

J answer (1)

#orrect ans$er $ith no $orkin" scores full marks 3[1 ]

14. 2

[1]

1 . #[1]



18/122

1#. D[1]

1 . (a) D 1

(b) # 1

(c) 1[3]

1$. D [1]

19. (a) (& 0 0 48 3 0 2'-8

)= 11 , 0 48 ' / 1 ,' 0 48 ' / 1 & 0 48 '

llo$ . from a 1

(b) @ r = ( 3 + ' ) = &, (1)

@ass = ( 0 7- 0 62-8

) (1)= 40/ 40 3" (1) llo$ . from (c) 3

*eject rong unit eg kg

(c) decrease 1

(d) HG# (i) ? (iii)

Codium is haFardous (1)

@ay "o on fire $ith $ater/ produces flammable "as $ith $ater/produces e*plosi e "as $ith $ater/ produces stron" alkali $ith$ater/ reacts $ith moisture on skin and becomes hot /corrosi e (1)

nd mark depends on reference to sodium

*eject unspeci!ic comments a"out sodium "eing poisonous / to-ic / !lamma"le ithout re!erence to ater

[$]



19/122

20. (a) (i) ''10 1

(ii) 0 01, 1

(iii) ( 1'&'4/ 8&84-) 5 1 2*' %9 mol 14

:alue (1)7e"ati e si"n and units (1). for ans$er to (i)/ ans$er to (ii)

(i ) HG#

ny t$o ofA

?se an insulated container/(e*panded) polystyrene cup?se a lid?se a thermometer calibrated to at least 0 , .C 2

(b) (i) HG#

7o effectB as all copper nitrate reacts any$ay (1)

nthalpy chan"e is based on mass of solution heatin" up/ C;# of the metal is ery lo$ (1)

(ii) HG#


20/122


21/122


22/122

(b) (i) / R

*e!erence to atoms or molecules or 4 2 or 5 2 scores(0) overall

F/RS AR!5

/ R

iodide (ion) lar"er than fluoride (ion)

$ccept just iodide has smaller charge density than!luoride scores first mar6

OR

Cum of ionic radii in "! lar"er (than in " )

$g 78 scores (0) overall

OR

halide ion or M 1 or anion increases in siFe do$n "roup (1)

$ccept atomic radius of halide ion 8 /anion increases4do n group6

S -OND AR!5

#har"es (on anions) same (1)

/RD AR!5

(so) $eaker (forces of) attraction bet$een ions (in "!) (1)

$ccept 9ea6er ionic bonding (1)

*eject just 9ea6er bonding )in :g5%)**+ 3 *+C+*S+ $*' +(3S $( S )*+ $LL 3 + $* S

OR

First and second com>ined >: statin

! 1 (ion) lar"er than 1 (2)

$ccept just iodide has smaller charge density than!luoride scores only one mark

/RD AR!5(so) $eaker (forces of) attraction bet$een ions (in "!) (1) 3

$ccept 9ea6er ionic bonding (1)

*eject just 9ea6er bonding )in :g5%

IGNOR !N" R # R N$ % &O 'O !RI%!&ION O# ION% !N" H R IN (*)(i)



23/122

(ii) .heoretical alue (assumes) 100> ionic 89no co alent character (1)

( *perimental alue is different) due to co alencyOR co alent character OR polarisation o% anion(1)

ention o! :g78 ; molecules scores (0)

(iii) (as) siBe o% anion increases (do$n "roup) (1)

$ccept atomic radius of halide ion 8 /anion increases4do n group6

.ention of :g78 ; molecules scores (0) unlessalready penalised in (*)(ii)

(anions) more easi : =o arised (do$n "roup) ORmore distortion o% anion (do$n "roup) (1)

$ccept more co-alent character more co-alent for second mar6

e


24/122


25/122

(c) (i) @ultiplies the 5;#8 3 e uation by (1)

and subtracts the 5 #8 3 e uation from it (1).his can come from a cycle

P > P 1 P 1 scores these first t$o marks

if P > P 1 1 2P loses second and third marksif P > P 1 + P loses second and third marks

P > P 1 P 1= (+ 4 3 0 2) 1 (1' ) %9 mol 14

= (+)101 & (k mol 14) (1)!6789 C#orrect ans$er plus some $orkin" (3)

$ccept 4=61:1 5 i! candidates uses !2#' from )b%#

ailin" to multiply by loses first mark abo eB but can thenscore ma* as follo$sAP > P 1 P 1 (1)

= + 4 3 1 (1 ' ) %9 mol 14

= (+)% 3 k mol 14 (1)..hird mark is conse uential on candidate ans$er in (b)Be " if (b) e uals + '3 k mol 14 the ans$er $ill be(+)1, &/1, % k mol 14 3

(ii) HG#reaction in solution produces ; 8(l)$hereas thermal decomposition produces ; 8(")89$ater produced in the decomposition is "aseous $hich isnot the standard state89ener : is re uired to apourise (li uid) $ater 1

*eject heat required to vapourise ater must "e takeninto account



26/122

(d) First mark5- c is smaller as %or*ard reaction is endot ermic (1)

+quili"rium moves to le!t and so - .alls scores 4:6

Second mark5

.he second mark can only be a$arded if the amount of reactant/productchan"es >eca'se of a chan"e in c

!ncreases the amount of 5;#8 3 /reactants89decreases amount 5 #8 3 /products (1).!f c is said to be lar"erB then the second mark can be a$ardedconse uentially for sayin" that the amount of 5;#8 3 decreasesB etc

$ccept equili"rium shi!ts to the le!t

*eject more ) # than 2 ) #[10]

2#. (i) 3C (s) + 8 (") + ; (")

correct entities (1)state symbols and balancin" (1)

(ii) ner"y chan"e $hen 1 mole of a compound is formed (1)

from its elements (in their standard states) (1)

at 4 5/ uoted temperature and 1atm (1) 3

(iii) ( 0 12 -& ) 1 (12*7& +(2 0 128&7)) (1)= 12 &7/12 ' (%9 mol14) (1)

llo$ transferred error for one minor slip (e " 0 ' instead of 0 &)but not for omission of multiples!"nore units

*eject 233 e


27/122

2 . (a) 7/7 "oes from 0 to 1 5 reduction (1);/; "oes from 0 to (+)1 = o*idation (1)

&!the oxidation number of ? goes do9n hence reduced and theoxidation number of / goes up and hence oxidised ) /a 1 6

&! all ) ( correct "ut !ails to state hich is o-idation andhich is reduction scores 1

&! all ) ( correct "ut "oth reactions misclassi!ied, scores


28/122

(c) (i) HG#8ne $aytemperature increase therefore molecules ha e "reater (a era"ekinetic) ener"y (1)

$ccept moving !aster

more molecules/collisions ha e S act (1)

.herefore a "reater =ro=ortion of/ more o% t e collisions aresuccessful (1)!"nore "reater fre uency of collision

$ccept + F + act particles !or moleculesgreater !requency o! success!ul collisions/ moresuccess!ul conditions per unit time

*eject just more successful collisions

nother $ayaddition of (iron) catalyst (1)

$ccept platinum catalyst

*eject incorrect catalyst

pro ides alternati e route of lo$er acti ation ener"y (1)

!.; 9A "reater proportion of /more of the molecules/collisions ha e S cat /a "reater proportion of collisions are successful

*eject just more successful collisions

89 pro ides (acti e) sites ($here reactant molecules canbond / be adsorbed) (1)

!"nore any ans$ers referrin" to pressure or concentrationDo not penalise Oust


29/122

2$. (a) (i) @ass = , + %, = '% %, (1) or in e uation belo$'% %, 0 '&4 0 48&- 5 28*7 (9) (1)(= 100 ( ))conse uential on calculated mass

$ccept correct ans er ith some orking (,)se o! incorrect mass 4e g m > 1 g6 can gain 2 nd mark

$ccept ans er changed to k%

(ii) @oles ($ater)= 4888-&42-

= 0 03%, (1)

D; = )8 6-&4888(28*7

)(

(1)

7 1--&* (%9 mol 14) (1)both alueB in k mol 14K and sign neededTignore $UM

$ccept correct ans er ==#' or ="#0 6* mol 1 ith someorking 4#6

D > #03(=%)10002100

%) (1)

="#0 )6* mol 1 6 (1)scores !ull marksonversion to k% can "e at !inal stage

(b) ny one of 7o heat is lost (to the surroundin"s)89Polystyrene cup or thermometer ha e ne"li"ible heat capacity89

ll the acid $as transferred (from the beaker) to the polystyrene cup 1

$ccept takes up negligi"le heat [#]

29. (a) (i) P & 1

(ii)-

-

24

!H 2

/ /

1

*eject D 5

Sri Lankan School 2?


30/122

(b) ither P ! > P = P 3 = P ' = P , = P &

89P ! = (+1% ) + (1%3,) + 0 (+24 ) + 2 0 (16 ) + (12 *)

5 14 7 (%9 mol 14) (1)#orrect ans$er $ith no $orkin" (2)

&gnore k%

GBirst mark only i! dou"les "oth @/ at and electron a!!inity!or hydrogenH

G2nd mark is only consequential on !ailure to multiplyeither @/ at or electron a!!inity or "oth givingI 7!0! 7

113 7331 )6* mol 1 6H

=187 scores (0)

=.:. / =11# /=##1 scores (0)

Sri Lankan School #:


31/122

(c) / RFirst mark5@a"nesium/@" ion smaller (radius) than calcium/#a ion8r the sum of the ionic radii in @"; smaller (than in #a; ) (1)

$ccept magnesium ion has greater charge density thancalcium ion !or !irst mark

*eject re!erence to atoms or molecules or / 2 scores Beroo2erall

Second mark5but char"es the same (1)

ird mark5(so) stron"er (forces of) attraction bet$een ions (in g ) (1)

J#orrect re erse ar"uments can score both marksK

$ccept stronger ionic "onding for 3 rd mark in eithercase

&!/ = ions or hydrogen ions referred toC 3 rd mark cannot"e a arded in either case

&! juststronger bonding in .g/ 2 C 3rd mark cannot "e

a arded in either case

ORFirst and second mark com>ined5g + (ion) or g + (cation) smaller (radius) than a + (2)

ird mark5(so) stron"er (forces of) attraction bet$een ions (in g ) (1)

J#orrect re erse ar"uments can score both marksK

!"nore references to polarisation of the hydride ion or


32/122

(b) (i) 0 2'4&8

= ' 1% 0 48 1 / 0 00'1% 1

$ccept : ::.17 4recurring6 $ccept : ::.2

*eject : ::.*eject : ::.17

(ii) @oles of ;#l at the start = 0 (1)@oles of ;#l reacted = 0 8&88'46

5 8&88 ' (1)

@oles of ;#l left = 0 1 8&88 ' 5 8&4*477 (1)

i"nore sf 3

$ccept trans!erred error !rom 4"64i6+g : 1?2

: 1?19

*eject : 2

$ccept : 1?7 4!orgetting to multiply "y 26orth ma- o! 2

(ii) *es labelled and suitable scale 1 must co"er more than half the pro"ided grid and time must be on the horiXontal axis (1)

ll points plotted accurately and suitable cur e/strai"ht lines (1)rom 0 to 1 minuteB must be strai"ht horiFontal linerom 1 to minutesB ertical or slopin" line to , 3 or abo e rom to & minutesB strai"ht line or smooth cur e

*eject temperature scale starting at : +, )1 max%

(i ) ner"y chan"e = ' 0 488 0 '&-5 4& * (%9) 4

$ccept 18?: 4%6 $ccept 1 ? 4k%6

$ccept 1?:: 4%6 $ccept ith either = or or no sign

e


33/122

( ) D; = 88'46&8+*&4

= 1'- %9 mol 14 (2)1 mark for number and 1 for si"n and units

$ccept 3+ !rom 4"64i6 and 4iv6Second mark dependent on the !irst

( i) ither lines dra$n on "raph to sho$ ma*imum temperaturerise should be ' ,8r Come heat loss (and so the readin" of ' 3 $as too small) 1

$ccept ma- temperature "et een 1 and 2 minutes

*eject rounded up to nearest : 5

(c) (i) ' + 1 + 3 * 1& = ' (") (1)

7umber of moles = / ' = 0 0 & / 0 0 &14 (1)!"nore sf e*cept if only 1 (i e 0 03)

$ccept : :27

*eject : :271*eject : :2

(ii) P 5 8272&8

8-&4

= 1 '8&4 %9 mol 14 1

$ccept correct sign and units needed !or mark $llo instead o! k !0#131 :llo9 EF from )c%)i%

e


34/122

(e) lements don ;t react together to form magnesium carbonate 4

*eject hard to measure temperature o! solid [1$]

31. ',, & + ' 0 424&6 (' 0 '86&')

ultiples (1);ess applied (1)= 17 6(&2) %9 mol 14(1)i"nore si" fi"!n "eneral deduct one mark for each mistake8ne $ron" or missin" multiples ( ma*);ess the $ron" $ay round ( ma*)7o si"n $ith ans$er ( ma*)*amplesA +1&4 4 (no multiples at all is t$o errors) (1)

148-2& /+- - (either multiple missing) (2) 1* 8&7 (2 0 Cl atomisation) (2)+& % (;ess misapplied) (2)+10, 3/ 1- -/+* 8&7 (1)

147*&*(0)[3]

32. (a) #orrect ans$er %3 1 $ith some $orkin" (2)

$ccept 9# :5 g / 9# :7 g / 9# g

.here are se eral $ays of achie in" this

e "(molar mass) #; ' = 1& (" mol

14)

89 (molar mass) #; ' = 1 + ' (" mol 14) (1)

24*474888

= %3 1 (1)

8914 k is produced from 1& " of #; ' (1)

1000 k is produced from 24*474888

= %3 1 (1)

89

7umber of moles #; ' = 24*4888

= ' ,% (1).he mass of #; ' = ' ,% 0 47 5 6 &4 (1)

$ccept 8: g ma- 1nd mark is conse uential on their molar mass

!"nore si" fi"s in final ans$er 2?. 'nits essentia

Sri Lankan School #.


35/122

(b) HG#

C + 2 C l

a

' 2

C + ' C l

#; ' + ( )#l and # + (');#l at correct le els (1)

P correct / 124* (1)

acti ation ener"y hump (does not need to be labelled) (1)

$ccept

o r

dou"le headed arro

*eject activation energy hump sho n as straight lines

*eactants and products @/

*planationA

9eaction/it has a i acti ation ener"y (1)!6789 reactants/methane and chlorine are kinetically stablein combination $ith hi"h acti ation ener"y

u pro ides ener"y to break #l 1Cl bonds (1)89#l radicals are produced in the presence of u

*eject C provides the reactants ith energy toovercome the +

a

!6789 any references to thermodynamic stability ,[ ]

Sri Lankan School #5


36/122

33. (a) HG#

enthalpy / ener"y / heat chan"e $hen 1 mol of a substance (1)

$ccept heat / energy / enthalpy released $ccept "oth element and compound instead of substance

e


37/122

34. (a) !n (a)(i)B (ii) and (iii) penalise 1C on the first occasion only ## P. S 2$U

(i) @ass methanol burnt = 0 3' (") (1)

2

'&8

= 0 010& (1)

$ccept : :11, : :1:7#, : :1:725 J on incorrect calculation o! mass

orrect ans er ith some orking (,)

(ii) .emperature rise = '3 , 1 22 (5 24&-) (.C) (1)

(;eat ener"y =) 4888-84+&'-&24

= ' '4 (k ) (1)

.he temperature rise mark can be scored from the heatener"y e*pression

$ccept J on incorrect calculation o! temp


*eject ans er in %oules

(iii) 8487&8'*&'

(i)Answer(ii)Answer =

(1)

$ccept J on 4i6 and ii6= 1'22&* (%9 mol 14) Jcalculator stored alueK

$ccept ans ers in the range !20 to !2!

89= 1'2 &7 (%9 mol 14) Jusin" rounded aluesK (1) min'ssi n and &a 'e >ot re 'ired


!f the final ans$er is incorrect the nd mark is onlyaccessible if ener"y is di ided by moles in first part of calculation

(b) (i) -&248&4

0 488 5 (Y)'&7- ZILR!H $U 4



38/122

(ii) ( 1 , + 1 0 =) , ( .C)!H ('' 1 24&-)522&- (.C)!H

4887-&48'

-&24 = , ( .C)

C[ on Z error in b(i) if this is used to calculate the temperature 4

*eject all other values

(c) (i) aporation (of methanol/alcohol) 1

$ccept turns to vapour )* methanol volatile

*eject "alance !aulty or spills or ethanol reacts

(ii) #arbon (1)

Eo$er/less e*othermic (1) i"nore references to incompletecombustion

$ccept soot

*eject any other su"stance[11]

3 . (a) (i) @" + (") (+) 8 1 (") 1

*eject i! state sym"ols missing

*eject i! 2e included in "o-

(ii) P 1 ( nthalpy of) formation (of @"8) (1)

P ( nthalpy of) atomisation (of @") (1)

P 3 1st plus nd electron affinity (of 8)

89 1 st and nd electron affinity (of 8) (1) 3 $ccept recognisa"le a""reviation such as F: forelectron affinity#



39/122

(iii) P ! = 1782 5 (+4-8) + (+24 7) + (+2'*) + (+7-6) + L+ 89(E =) 1(+7-6)1(+2'*)1(+24 7)1(+4-8)+(1782) (1)

Dou"ling electron a!!inity and/or atomisation valuesscores (0)

(E =) 1 '' (%9 mol14) (1)

#orrect ans$er only $ith no $orkin" (1 maC)

*eject any incorrect sign in alge"raic e-pression (0)

(b) (i) .he electrons around the iodide ion are dra$nto$ards the ma"nesium ion 1

$ccept 4 g 2= 6 polarises 4& ion6 $ccept distortion if clearly lin6ed to the iodide ion

:ccept .g ion :ccept 5 ion ; iodine ion

e


40/122

(iii) Eess (e*othermic) (1)

$ccept Smaller )* more endothermic )* Less negative)* Lo er

*eject higher/greater

co alent character (stren"thens lattice) (1)

$ccept theoretical value "ased on purely/1:: K ionicmodel

*eject any implication o! magnesium iodide "eing totallycovalent

@ark each aspect independently[11]

3#. (i) nthalpy chan"e $hen 1 mol of "aseous ions (1)

$ccept energy or heat

*eject any implication o! an endothermic processe g energy required

*eject I#1 mol of gaseous ato/s

is dissol ed such that further dilution causes nofurther heat chan"e (1)

$ccept added to 9ater reacts 9ith 9ater instead ofdissol-ed

e


41/122

(ii) / R

P S)L( = ( 1P L+ + P ED ) (1)*pression uoted or correctly used in at least one of the calculations belo$

$ccept ans er only ith no orking (1)P S)L( gS) ' = 1(12 6') + (14*28)

5 +*-' (%9 mol 14) (1)

P S)L( = @aS) ' = 1(12 6') + (14 78)

5 +484' (%9 mol 14) (1)

$ccept ans er only ith no orking (1)

nthalpy of solution of @"C8' less endothermic/moree*othermic/more ne"ati e than for 2aC8 ' B so @"C8 'more soluble than 2aC8' (or re erse ar"ument) (1)

*eject just solubility @/ soln depends on a "alance"et een lattice and hydration energies

OR(both) lattice ener"ies and hydration enthalpiesdecrease from @"C8 ' to 2aC8 ' (or do$n "roup) (1)

$ccept Ehe hydration energies decrease fasterI##

e


42/122

(b) (i) P = (+40 0 ') + (1 2'2 0 7) 1 (1 '7&4 0 ')

= 1 *86 (%9 mol 14) (2) !6789 sf

#orrect ans$er $ith no $orkin" scores (2)8ne mark for correct use of all three coefficients

8ne mark for correct use of si"ns throu"hout

(ii) 1 427 (%9 mol 14)!6789 sf 1

(c) (i) 2ecause it is the more e*othermic 1

(ii) HG#

chan"es the acti ation ener"y for a reaction by chan"in" themechanism/route (1)

lo$ers it for 9eaction ! more than for 9eaction !!89 catalyst specific for 9eaction ! (1)

J#omparison is essentialK

(d) (i) .o protonate the nitric acid89 to "enerate 78 +

89 increases the concentration of 78 + compared $ith nitric acid alone

(1) !6789 comments concernin" ; C8 ' bein" a catalyst; C8 ' + ;78 3 ; 38

+ + 78 + + ;C8 ' 1

or ; C8 ' + ;78 3 ; 8 + 78+ + ;C8 '

1 (1)or both ofA; C8 ' + ;78 3 ; 78 3

+ + ;C8 ' 1 then ; 78 3

+ ; 8 + 78 + OR

; 78 3+ + ; C8 ' ; 38

+ + 78 + + ;C8 '

&! candidate says to generate the electrophile, the markcan "e a arded i! () 2

= is sho n in the equation

(ii) sulphuric acid protonates nitric acid

89 nitric acid accepts a proton / ;+ from the sulphuric acid (1)

ns$er may refer to the e uation formin" ; 78 3+ 1

*eject just / 2 S) . is di"asic and () # is mono"asic or similar arguments

Sri Lankan School .2


43/122

(iii)

R !2+

R !2

+

R !2

+ R !2$ ! '

+ $ !2 '

1

allo equivalent using the circled sym"ol !or "en


44/122

(ii) 8&6'88&4

= 0 013, mol ns$er must be decimalised 1

$ccept : :1.

*eject (!1

/ : :1

(iii) P 1 = 84 -&8-&46 2

= 14 8 (%9 mol 14) ( s f )

P = 84 -&8-&2766

= 1288 (%9 mol 14) ( s f )

1st mark for method (di idin" ener"y by number of moles)nd

mark for both ans$ers "i en to si" fi" and includin"ne"ati e si"nsnd mark is dependant on 1 st

$llo 3+ !rom 4a64i6 and 4a64ii6

(b) (i) P reaction = P 1 1 P /rele ant alues bein" subtracted (1)

= 14 8 1 (1288) 5 + 68 %9 mol 14 (1)@ark independentlyor nd markA correct arithmeticB si"n and units needed

$llo 3+ !rom 4a64iii6&gnore sig !igs

(ii) ?sin" a ass >eaker / no lid is likely to lead to heat loss (1)("lass) >eaker has si"nificant heat capacity (1)7o apparent check made to ensure that #a(8;) $as heatedlon" enou"h/difficult to kno$ $hether #a(8;) $as fully decomposed (1).he likely use of an insufficiently accurate t ermometer (1)

ny .G8 alid and a"reed sources of error

(iii) @easurin" temperatures of solids ($ith a lab thermometer )isn ;t accurate / is difficult (1)2unsen/hi"h temperatures are in ol ed (abo e bpt of ;"/ethanol) so lab thermometers can ;t be used (1)Difficult to kno$ $hen #a(8;) has fully decomposed (1)6i en hi"h temperatures in ol edB impossible to usethermometer to measure ener"y taken in by the #a(8;) (1)

ny 87 of these 1[9]

Sri Lankan School ..


45/122


46/122


47/122

(ii) disad anta"e(plant more) e*pensi e because thicker pipes $ould be needed

)* cost (of ener"y) for compressin" the "ases/cost of pump89#ost of e uipment/pressure not Oustified by hi"her yield 1

$ccept stronger or ithstand high pressure !or thicker

$ccept vessel/container/plant /equipment/reactionvessels !or pipes

*eject


48/122

41. (a) (i) 2r @ #r (1)state symbols (1) 2r (") @ #r(g) scores only one

e "

2r (l)@ #r(g) (2)2r (l)@ 2#r(g) (1) ie for state symbols2r @ #r (0)

*eject rong halogen or use o! 8 (0)

(ii) ner"y chan"e $hen 1 mo (1)

$ccept heat or enthalpy !or energyenergy released instead o! energy change

*eject energy re uired

of a solid/crystal/lattice (1)is formed from its (isolated) "aseous ions (1)!6789 standard states 3

%ust "alanced equatione g (a =4g6 = l 4g6 (a l4s6can score only last t o marks

(b) @"#l has (a de"ree of ) co alent character (1)

ention o! atoms or molecules scores (0) !or all o! 4"64ii6

due to polarisation of the anion (1)(by g + cation)

*eject just .g 2= 4strongly6 polarising

Sri Lankan School .8


49/122


50/122

(b) measurin" cylinder 1

$ccept "urette $ccept pipette $ccept volumetric pipette $ccept graduated pipette $ccept 5: cm # pipette $ccept pipette > pipette !ilter $ccept reasona"le phonetic spelling e g pipet, "iurette

*eject "eaker *eject "iuret *eject graduated !lask *eject volumetric !lask *eject "eaker or a pipette*eject pepite*eject conical !lask

(c) ny t$o

polystyrene conducts heat less $ell than metals/less heat lostto surroundin"s (1)

$ccept discussion o! either polystyrene or metal

has a lo$er (specific) heat capacity/absorbs less heat ener"y (1)

Plastic inert $hereas metal container mi"ht react ($ith #uC8 ' ) (1)

(d) Linc ,/&, ' = (0 0%&,/0 0 /0 0%&/0 %%) (1)

#opper sulphate ,0/1000 = 0 0, (1)

#opper sulphate / #u + / #uC8' (1)

$ccept consequential on copper "eing less than


51/122

(e) (i)

6 8

7 8

- 8

' 8

8

2 8

4 8

8

F e m p e r a t u r e/ \ C

8 ' 8 8 4 2 8 4 7 8 2 8 8 2 ' 8F i m e / s

a l lo w e i th e r

correctly plotted points (1) 1 All 6 (including 8K 22)must be correctly plotted

points Ooined by suitable lines (1)

$ccept curve/straight lines

J!f you cannot see a lineB check t$iceB if still not isible send tore ie$ as out of clipK

(ii) reaction not instant / so some time before all heatener"y released/measured (1)

$ccept energy lost

(temperature (slo$ly) declines) as heat ener"y "i en out(to the surroundin"s) (1)

*eject no temp change !or !irst 7: s "ecause


52/122

(f) (i) ,0 0 '&2 0 '- 5 *'-8 (9) for 76.C

!"nore units unless alue and units are incompatible e "4 '0 k (0)4 ' (0) 1

$ccept 3+ !rom e4iii6e g77 > .. + rise & '2!0"$ & !" + rise & '""0"' & !( + rise & '$(0"= & !3 + rise & '030):llo9 minus sign% ignore sign(0 & !$ + rise & 100$0"=#= & !3#= + rise & '13=allo9 use of "=+ e-en if different -alue in )iii%

e


53/122

(iii) !ncomplete combustion / combustion to # or #8 7otcomplete combustion (1) 1

*eject not all o! the propane "urns

*eject comments on accuracy o! equipment

(b) (i)C ( g ) +5! 2( g ) C !2( g ) + ' 2! ( g )

+ 7 ' * 8 % 9 m o l 1 4 6 8 0 5 + 8 4 6 4

C ( g ) + ( g ) +1 0 ( ! )+&'40 = P c + (& 0 8- + 0 '7')P

c=+&'40 1 ' 8 1 642

5 128-2 %9 mol 14

$ccept 20=0 )6* mol 1 6

2alancin" cycle $ith 8 and 10 O ( ) (1)P 1 = (& 0 8- + 0 '7') 5 (+) -'2 (%9 mol

14) (1)

inal alue 128-2 (%9 mol 14) (1)&'()*+ SB

$llo 3+ !rom an incorrectly calculated @/ 1 i! method clear 3

(ii) ; 8 is "as in e uation/ not standard state89 mean bond ener"ies differ from bond ener"ies in thesecompounds / n ironment in these compounds chan"es bondener"ies from the mean 1

$ccept 2 ) is liquid in @/ combustion calculation but ges inbond energy calculation#

e


54/122

(ii) # 3; %J @ C &; 1' (1)

.$o (propyl) radicals may combine /a radical and amolecule may produce # &; 1' (in a propa"ation step) (1)

$ccept # 9 M L , # 9 M N , 7 1. (1)

$ccept multiples

$ccept # 9 M L , # 8 N , 7 1. = M(1)

Bull mechanisms may "e sho n

(d) (i) -chloropropaneA $hite precipitate/ solid /cloudiness (1)

*eject hite colour

*eject creamy

-iodopropaneA yello$ precipitate / solid (1)

$ccept ppt appears slo ly ith chloropropane and quickly ith iodopropane (1)

$ccept pale yello precipitate

$ccept hite colour and yello colour 1 out of 2

(ii) " +(a ) + ! 1 (a ) @ AgI (s)

Uormulae (1)Ctate symbols (1)

@inor error in formula $ith correct state symbols ma* 1 $ccept ma- 1 out o! 2 !or rong halide

(iii) Propan- -ol/ #; 3#;(8;)#; 3 (1) 1

$ccept displayed !ormulaC 1C ? C

!

*eject molecular !ormula # 9 ) [1 ]

Sri Lankan School 5.


55/122

44. (a) (i) B B'-trimethylpentane!"nore punctuation (#ommas and hyphens may be interchan"ed) 1

$ccept 2,.,. M trimethylpentane

*eject pentan !or pentane

2MdimethylM.methylpentane2,2MdimethylM.Mmethyl

pentane2MmethylM.,.Mdimethyl

pentane2,.Mtrimethylpentane

(ii) # ' ; 4 1

$ccept 8 18 N , . ?

(iii) # ; ' 1

*eject 2 2

(i ) Positi e because ener"y is re uired to break (# 1C) bonds(and not completely replaced (from new bonds made))!H >ositi"e because crac%ing reVuires (continuous) supply of heat so must be endothermic 4

$ccept t o , bonds are bro6en and one ,&, made

e


56/122

(b) (i) !ncrease in pressureA 7o effect as number of moles/molecules (of "as) doesn ;t change during reaction (1)

!ncrease in temperatureA more NO as for$ard reactionendothermic 8G.. (1)

8ne mark for t$o correct predictions $ith incorrect e*planations*eject increase in temperature moves equili"rium to theright

(ii) 9ate increases as con erter "ets hotter (as reaction ise*othermic) 1

(iii) 7 / nitro"en is (maOor) part of air/ 7 unreacti e/ notpoisonous/ not a "reenhouse "as / not acidic 1

$ccept correct harm!ul properties o! other # gases

(i ) Eine from le el of reactants to ma*imum labelled (1)

#ur e of similar shape abo e e*istin" cur eB startin" andfinishin" at same le elsB $ith ma*imum abo e ori"inal ma*imum (1)

[12]

4 . (a) ;eat/enthalpy/ener"y c an e per mole of substance/compound/product

)*

heat/enthalpy/ener"y c an e for the formation of 1 mol of substance/compound/product (1)


57/122

(ii) .he e uilibrium mo es to ri"ht hand side

)* amount of dissociation increases (1)

2ecause the (for$ard) reaction is endothermic (1)

(eeds to "e consistent ith 4i6

&! 4i6 has a negative ans er 4e-othermic6

e uilibrium mo es to left hand side (1)

2ecause (for$ard) reaction is e*othermic (1)

&! ans er to 4i6 is =?# or ?# "ut state that this is e-othermic !f reaction mo es to left hand side (1)!f reaction mo es to ri"ht hand side (0)

(iii) add chlorine (1)$hich dri es e uilibrium to the left (1)

)* increase the (total) pressure (1)because there are fe$er ("as) molecules on left hand side (1)

)* add P#l 3 (1)Ghich dri es e uilibrium to the left (1)

[$]

4#. (a) (i) enthalpy/heat/ener"y chan"e/produced J78.


58/122

(c) (i) cycleAfor each labelled arro$ Ooinin" correct species

g ( ! ) ( s )D a t t i c e n e r g y

g ( a V ) ( + ) 2 ! ( a V )

/

h y d r a t i o n

s o l u t i o n

g ( g ) ( + ) 2 ! ( g )

12 +

2

/

12 +

Cpecies and stoichiometry (1)Ctate symbols (1)Eabels appropriate to direction of arro$s (1) $LL) numerical values

$LL) cycles usin" -E 3

(ii) D solution = - E + ^ D hydration )* numbers (1)

" kJ mo 1

(1)onsequential on candidate s cycle eg calculation from cycle $ith one 8; - "i in" +,,, k mol 14 (2)@ 3 correct ans er ith orking (2) even i! the 4c64i6 cycle is rong

(d) #alculation of D solution of 2a(8;) as -,, k mol 14

)* E do$n by &%, but D hydration do$n by &1,

$LL) E do$n but D hydration do$n by less (1)

Q D solution

is more e*othermic (1)

Q solubility is "reater (1) 3

2 nd mark dependent on 1 st

# rd mark dependent on 2 nd

$LL) conse uential markin" if D; solution ess e*othermic[1 ]

4 . (a) (i) e 8 3 + 3#8 e + 3#8 (1)

D = (3 0 1 *') ? ( 0 1448) 1 (1 22)5 1 8 (%9 mol 14) (2)

ultiply "y # t ice (1)orrect ans er ith sign (1)

$LL) consequential calculation i! rong stoichiometry &! )2 given as product 1 maC on consequential calculation 3



59/122


60/122

(e) (i) add (a ueous) sodium hydro*ide / ammonia (1) $LL) 8; 1 (a )red/bro$n/fo*y red/red-bro$n/rust ppt/solid (1)

)* add (a ueous) potassium he*acyanoferrate(!!)/he*acyanoferrate(!!)

ions (1)(Prussian) blue ==t6so id (1) 8 $LL) result !or near miss spelling o! reagent

)* add (a ueous) potassium thiocyanate (1)blood red (solution) (1) ()3 ppt

(ii) e 3+ polarises the (8; bond in $ater) li"ands (1)

J e(; 8) &K3+ + ; 8 J e(8;)(; 8) , K

+ + ; 38+

)* in ordse" deprotonation (of the li"and) >: the (sol ent) $ater (1)

the ; 38+ / ; +(a ) ions make the solution acidic (1) 8 stand alone 3

[19]

4$. (a) Difficult to decide $hen reaction complete/ reaction may be incomplete (1)

)* ll #a#8 3 may not decompose (1)

)* Difficult to measure temperature chan"es in solids (1)

)* P3 or P reaction cannot be determined because heat is supplied (1)

)* 7ecessary temperature cannot be reached (1)

)* 7o suitable thermometers (for measurin" temperature chan"e at hi"htemperatures) (1)

$LL) heat is re uired so temperature change 9ill not be accurate

()3 /eat is supplied so temperature cannot bemeasured 9ill not be accurate 1

(b) (i) 9eaction occurs uickly / incomplete reaction (in reasonable time)$ith lumps (1)

;eat losses occur if reaction is s o* (1)

(ii) ' 0 28 0 2&- 5 248 (9) )* 0 10 k&'()*+ =/M signs!ncorrect units (0) 1



61/122


62/122

(ii) 100 1 487. (1)

as lone / non-bondin" pairs take up more space/repel more stron : than bonded pairs (1)()3 bonds bein" repelled/; and #l bein" repelled

(c) 7o chan"e (1)

as number of aseo's reactant molecules = number of aseo's productmolecules (1)

$LL) 1 /a i! candidates state or imply a very small change ith correct justi!icatione"


63/122

(c) (i) P = P f (C8 3) 12 P f (C8 ) = ( 1 *- 0 2) 1 (1 2*6 0 2) (1)

= 14*7 (%9 mol 14) (1) &'()*+ units

14*7 (%9 mol 14) ith some orking (2)

(o consequential mark other than !ailing to multiply "y t o to get 1* %9 mol 14 maC (1) $ny positive ans er (0)

HG# (ii) P f is de%ined as formation from elements)* P f of an element is de%ined as 0 (in its standard state))* a elements are "i en the alue Fero

:It is an element; on its o n (0) 1

(d) (i) : 8 , )* : 0,()3 name()3 : 8 ,

&! name and !ormula given, ignore name 1

Sri Lankan School 7#


64/122


65/122


66/122

(b) (i) % 0 cm 3 $LL) Y 4&8 cm3 1

(ii) 4 3 Y 8&- .C 4

(c) (i) 48882(i)(b)

$LL) correct ans er ith no orking 1

(ii) (c)(i) 1

(iii) (c)(ii) 0 -84888

(1)orrect ans er see table belo9 (1)

(d) (i) ,0 + (b)(i) (1)

0 '&2 0 (4888)(b)(ii)

= ans$er (1)

ust use 4"64i6 in calculation to score 2 nd mark &! the units are given, they must "e correct

(ii)== (iii)(c)8&8-

(i)(d) /

ans$er plus units

si"n (1)

numerical ans$erB usin" candidate ;s figuresK to 2 or s&f& (1)k mol 14 (1) can "e in % or % 3

3a"le o! ans ers

(b)(i) (b)(ii) (c)(i) (ii)

(c)(iii) (d)(i)/

k

(d)(ii)/ k

mol

1

4

& 0 4 '4&

0 0, 1 0' 3 0030&

1 -6&6 1 -

&

27&- *&' 8&8- 4&87 &82 1 -6&8



67/122

*&7 &8 1 -

&4

26&8 *&'*&7

8&8-' 4&8 &8'&48

1 -7& 1 -6&'

(e) !nsulate calorimeter / (polystyrene) cup89 put (calorimeter) in a ("lass) beaker

)* put a lid on 1 [13]



68/122

3. (a) 7umber of moles /2

4/-8&86-& =

(1)&! candidate does !irst part only, orking must "e sho n

7umber of atoms = 3 01 0 48 3 (1) $ +03 3 0 )* 3 )* 3 010( 048 3 )()3 3 01 3

&! all orking sho n, allo 3+ !or 2 nd mark &gnore unitsorrect ans er ith no orking ( )

(b) (i) Ei((s)) + ; +((a )) @ 2 i +((a )) + ; ((")) $LL) multiples &gnore state sym"ols 1

(ii)

+ +D i

+

C l+

1

(1) (1)

$llo all dots or all crosses on l

a- 1 i! no/ rong charges&! covalent 4:6Do ()3 penalise i! electrons not sho n in pairsa-imum 1 i! Li and l not la"elled Li and l sym"ols can go "elo diagramSquare "rackets not essential

$llo num"er o! protons/positive charges in nucleus asalternative to sym"ols !or Li and l 2

(iii) ny t$o fromA

.emp 4 5/ , .C )*


69/122


70/122


71/122

(c) (i) @ r of butane is , (" mol 14) (1)

-+2+66 1

= 1'*&7 / 1-8 (%9 g 14) 1 conseVuential on r (1)

(ii) comparison of any t$o or three fuels by mass (1)

" # ' ; 10 "i es out most ener"y per "ram

comparison of any t$o or three fuels by olume (1)" # ; 1 "i es out more heat than ethanol per cm

3

comparison of states e " # ' ; 10 "asB # ; , 8; and # ; 1 li uids (1)

and conse uence of state on use as fuel in motor ehicle (1) '" "ases need bi" fuel tank to be stored at hi"h pressure

)* li uids need smaller tank

[13]

. (a) (i) Points accurately plotted (1)

*o strai"ht lines of best fit (1)()3 dotMtoMdot, &'()*+ any other joining up#

(ii) Cuitable e*trapolation to find ma*imum temperature rise at 3 W min (1):alue from candidate ;s graph 0 , .C (1)

('3 ,-'' , .C for accurate plot) 2

(iii) (.he best fit line) allo$s for coolin" effect)* heat loss)* calculation of more accurate temperature c an e)* response time of the thermometer )* slo$ness of reaction()3


72/122


73/122

$. (i) Potassium ion / 5 + lar"er than #a + (1)ust not re!er to atoms

HG# 5 + smaller char"e than #a + (1)@ust not refer to atomsB but # 7 say


74/122


75/122

(iii) P = 4888(7 8/8&8-)

= + 13 k mol 14 J C Kans$er (i) (ii) (1)si"nB units and C (1)

2 nd mark dependent on 1 st unless clear method given $ns er can "e calculated in % mol 1

+ 13 k mol 14 ith no orking (2)+ 13 000 mol 14 ith no orking (2)

(i ) .emperatureB since PF is so small (and therefore leads torelati"ely large Z error) / thermometer has limited accuracyeat loss / gain not su!!icient 1

( ) .hermos flask / (e*panded) polystyrene/plastic cup / a beaker contained in a lar"er one la""ed $ith cotton $ool)* #alorimeter (un ualified) (0) @ 3


76/122

(ii) lectron pairs/electron clouds repel allo$in" bi""er an"lesin three dimensions)* !t is a three-dimensional shape bein" represented in t$odimensions

)* *planation of $hy an"les are not 40 . in C 3 / are not 1 0 .in C! (1)

;#8 or ;#; = 104 . / 48*&-.!H C! 5 48 ?48-. (1)

$ngle can "e stated rather than marked on the diagram "ut must "e "et een t o "onds, not "et een t o atoms

$LL)


77/122


78/122

( )

;ydro"en bond/ dotted line bet$een 8 in one molecule andhydro*yl hydro"en in another (1)

2ond an"le 1 0 . (1) 1 must go across 2 nd mark depends on correct atoms in "ond

$LL) diagram sho ing methanol/ethanol ()3 diagram sho ing methanol/ethanol and ater

$LL) minor slip eg one missing on a #

(d) .emperature

Eo$ temperature as for$ard reaction is e*othermic / re erse reactionuses heat / endothermic (1)

Eress're

Pressure hi"h as number of molecules/moles is decreasin" / fe$er /3 molecules/moles "o to one (1)!f numbers specified must be correct()3 molecules "o to 1()3 "ases "o to 1

+-planation using Le hatelier is !ine @ 3 not He ,hatelier on its o9n $LL) 1 mark !or correct choice o! temperature 4lo 6 and pressure 4high6

ith some attempt at e-planation[1 ]



79/122

#2. (a) (i)

Ctarts at Fero and approachin" - -a*is (1)@a*imum "reater and at lo$er ener"y (1) 1 3

2 needs only to "e just

higher than 3 13 2 curve must go "elo 3 1 curve approaching the -Ma-is

(ii) s the temperature increases the ener"y of the particles increases (1)

?se the dia"ram shadin" areas)* more particles to the ri"ht hand side of line (1)

and so more (successful) collisions/particles ha e ener"y "reater /e ual or "reater than the acti ation ener"y (1)()3


80/122


81/122

(b) 2onds broken ' 0 C? 5 + 46'8

2 0 !5! 26 7**7

+=+=

(1)

2onds made 0 C5! 5 1 4748

' 0 1! '77 1 4+-7 1

== (1)P 5 + 26 7 + (1 '77) 5 1 6 8 (1) (k mol 14) 3

(c)

C ( g ) + 2 ! ( g ) C ! ( g ) + ' ( g )

' ( g ) + C ( s ) + ! ( g )

2 2 2

2 2

'

#ycle (1)do not allo the ord elements

$rro s la"elled D ! etc or num"ers (1)

P r = 1 *' 1 (1 6-) 1 2 0 (12'2) (1)

= + 1&, (1) (k mol 14) '[10]

#4. (a) Ctep !! Gait before readin" temperature/ take a series of

(temperature) readin"s (1)78. !"nore any references to time or more accurate thermometer

Ctep !!! Ctir after each addition / lea e thermometer in solutionthrou"hout/do not rinse (1)

(b) Dra$in" t$o best fit lines (second line can be throu"h first three points) (1)

*tendin" to a ma*imum (1)

#ur e bet$een 0 and , cm 3 scores first mark only7ote if use $ron" last point for first lineB no marks can be scored

;and sketched ($ithout ruler) scores one mark only

(c) 9eadin" PF conseVuentially (1) e*pected PF 5 6&8 Y 8&4 (.C) 2sf for PFHeading 7 conse uentially (1) e*pected : 7 = , to 3 0 (cm

3) 3sf for : 7

PF 5 7&* (.C) 7 = , 0 (cm3) scores (1) only



82/122

(d) (i) ;eat calculated usin" candidate ;s "alues in (c)ignore or more $U at this stage 4

(ii) ( 1) 82-&8))(( id to :ns9er

@ethod conse uentially (1) ns$erB si"n and 1' $U (1)

T Vol Heat/kJ H/kJ mol

1

% 0 , 1 34 55.6

7.0 23.0 1.40 56.0 / 56.2

& 4 , 0 1 '' 57.7 / 57.6

[9]

# . (a) ner"y/heat chan"e (1) $LL) nthalpy chan"e$hen "aseous ions (1) ()3


83/122

(d) (i)

( a V ) + ( a V )

1 /

/

l a t t

( g ) + ( g )

R o m e i n d i c a t i o n i t i s 2 - a l u e s

s o l n( s )

1+

+ 1

)* ener"y le el dia"ramCpecies includin" state symbols (1) $LL) 2=/2 ions

rro$s correctly labelled (1)!f E arro$ K must be shown as 1

$LL) a speci!ic e-ample e" 7a#l

(ii) P solution = 1 attice energy + ( ) hydration enthalpies

$LL) "alance "et een lattice energy and hydration enthalpies (1)the more e*othermic P solution the more likely the compound is to dissol e(1) 1 stand alone)* !f ( ) hydration enthalpies are greater than lattice energy (1).he compound (is likely to) dissol e (1)

(iii) ( rom #aC8 ' to 2aC8 ' ) the lattice ener"y chan"es by less than thehydration enthalpy / lattice ener"y chan"es by 10&B hydration by40 5 mol 14 (1) so enthalpy of solution process is more endothermic/

less e*othermic so solubility falls (1) 1 dependent on the 1 st mark [1 ]

Sri Lankan School 8#


84/122


85/122

# . (i) #l in ;#lA 14 / 4 1 Cl in Cl A 0(1)8 in ; 8 A 14 / 41 ! in 8A 12 / 21 (1)

(ii) hydrochloric acid/hydro"en chloride/chloride ion/ ;#l/#l 1

()3


86/122

(b) (i) D c = J( 1 *') + (2 0 12 7)M 1 (16-)M

5 1 *4 %9 mol 14

1 *4 %9 mol 14 $ith $orkin" (3) 178- %9 mol 14 $ith $orkin" (2)

all other :non?typo; "alues (max 4) for 2 0 2 7 1 *4 %9 mol 14 $ith no $orkin" (1) 3

(ii) (ne"ati e so) e*othermic(conse uential on (i)) 1

(c) # ; , 8; + 38 #8 + 3; 8species (1)balancin" (1)

(d) +,-ust compare the t o !uels !or !ull marks)nly data generated ad-antages and disad-antages to score#

@ethane is a "as and ethanol is a li uid plus a alid comment aboutstora"e in &e ic e B e " methane re uires ea&: container to store "asunder pressure / ar e container re uired to store "asB $hereas easy tostore li uid in fuel tank (1)

An: 2 o%

@ethane cheaper per k of heat released (than ethanol)

@ethane cheaper (per tonne than ethanol)

@ethane produces more heat per "ram (than ethanol)

heaper / more heat implies a comparison 3

(e) # ; , 8; + J8K #; 3#;8 + ; 8 (1) not #; 3#8;# ; , 8; + J8K #; 3#88; + ; 8 (1) (allo$ #; 3#8 ;)

llo$ #; 3#;8 + J8K #; 3#88; if #; 3#;8 is a product in 1st e uation

(f) conc ; C8 ' / l 8 3 / conc or syrupy ; 3P8 ' or names (1)or acidsB conditionsA heat (if temp stated conc sulphuric 1,0 .C1288 .C

phosphoric -8 to 488.C)Uor aluminium oxideK conditions pass "apour o"er hot Al 8 3 (1)

[1#]

0. (a) (i) , 00 + ' 0 = 0 0,4, mol 1

(ii) ,0 0 0 '&4 0 7&- (1) i"nore si"n 4888 (1) = 1 3&k mark conse uentially

(1 '4 k if use ,, 0 " (1) )



87/122

(iii) ns$er to (ii) answer to (i) (1) /correct method(e*pected ans$er + & to + 4 for ,0 0 " or + ' to + , 1 for ,, 0")

ns$er $ith positi e si"n to 3 sfs (1)

(b) (i) !ncrease temperature for 7a #8 3 and decrease for 7a;#8 3 (1)Ear"er D. $ith 7a #8 3 (or conse uential on (a)(iii) (1)

(ii) 7o heat lost/"ained to/from surroundin"s/reaction is completeshc of the solution is the same as $ater

llo$ 1 cm 3 of solution has a mass of 1" 1Do not allo$ shc is ' 1 " 148# 14

[$]

1. (a) (i) 12'8 (%9 mol 14) 1

(ii) 1 78 (%9 mol 14)Penalise incorrect units once only 1

(iii) 8 erlap of p-orbitals / p (system) (1)(results in) delocalisation (1)makes benFene (more) stable (by 1, k mol 14) (1)HG# 3



88/122


89/122

(b) (i) ' 1 0 488 0 4&4 (1)= '&0 / 0 '&0 k /',4 (1)

(ii) @r @"C8 ' %; 8 = '& (1)1 3/ '& = 0 0, (1) llo$ .

(iii) '&0/0 0,+4 00 mol 14 /+4 k mol 14 (1)si"n and units (1)

1 for incorrect C EE8G . from b(i) and/or b(ii)

(c) (i) D r = D 1 D 1

(ii) +4 1 1 -&25 +*' %9 mol 14 (1)si"n and units (1)

[1 ]

3. (a) (i)

1

$ +03 all dots/crosses

(ii)

.ri"onal pyramid/.etrahedral/ :Fhree leg stool; shape (1) 1 must "e some attempt at #D or correct name10%. $LL) 4 -10 (1)

(iii) repulsion bet$een four pairs of electrons "i es

tetrahedral shape (1) )6reater repulsion of non-bondin" electrons/lone pair closes do$n tetrahedral bond an"le (1)

Sri Lankan School 8?


90/122

(b) (i) P; 3(") P(") + 3;(") 1

(ii) ;ess applied (1)@ultiples (1)#orrect ans$er + 4&3( )/4&0 kJ mo 1 (1) 3

(iii) ns$er to (ii) di ided by 3+ 3 1( 1)/3 0 kJ mo 1 1

[10]

4. (a) (i) @ethanol is the bi""est/ most comple* molecule / "reatest @ 9 /mostatoms/most electrons 1

(ii) DCsystem = 34 % 1 4*6&7 1 2(4 8&7)

5 124*&4/ 124* 9 mol 1l5 14

@ethod (1)ans$er + units (1)

(iii) yes as 3 molecules 1 )* yes as ( ) "ases a li uid 1

(i ) DC surr = 1 D;/. (stated or used) (1)

= 1(142*/ 2* ) 5 +8&' %9 mol 14 5 14 / +'33 mol 14 5 14/+ '3 4 (1) 14 for wrong units/ no units / more than ' $U 14 for wrong sign/ no sign 2

(") DC total = 124*&4 + ' 5 +24 &* / +24 & 9 mol 14 5 14/ + 1' mol 14 5 14/

+0 1' k mol 145 14 (1)

Eositi&e so =ossi> e (1)

(b) (i) .emperature

aster at '00 .C (1)e en thou"h yield is lo$er (1)Pressure;i"her pressure impro es yield of methanol (1);i"her pressure increases rate (1)aCim'm 3 3

(ii) 7ot in same phase as reactants EE8G state instead of phase 1

(iii) p = p (#; 38;)/ p (#8) 0 p (; ) 1

(i ) Partial pressure of methanol = 00 1 -- 1 28 5 42- atm (1) p = (1 ,)/,, 028

= , & 0 48 1 / , % 0 48 1 atm 12 (1)

Sri Lankan School ?:


91/122

(c) (i) 7umber of molecules / fraction of molecules $ith ener"y + /number of molecules $hich ha e enou"h ener"y to react 1

(ii) :ertical line / mark on a*is to sho$ alue to the left of line + 1[1 ]

. (a) (i) nthalpy / heat (ener"y) c an e on formation of 1 mole of a compound (1)from its elements (1)in their standard states/ at 1 atm pressure and statedtemperature ( 4 5) (1) 3

(ii) ( 0 ') 1 (2 0 *8) (1)D = 1 442 %9 mol 14 (1)

+ 11 k mol 14

or 1-7 %9 mol 14

(1)

(iii) enthalpy chan"e conse uential on (ii) (1)acti ation hump sho$n (1)dia"ram properly labelled 1 D; $ith arro$sB named reactants andproducts (1) 3

(i ) Products thermodynamically more stable than reactants e*othermic 1

( ) 9eaction has a hi"h acti ation ener"y /reactants are kinetically stable 1

(b) (i) Dynamic 1 constantly mo"ing / still reacting/Hate of forward reaction eVuals rate of re"erse reaction (1)uilibrium 1 concentrations/ amounts constant (1)

(ii) position of e uilibrium mo es ri"ht (1)fe$er moles/ molecules on 9 ; C (1)

(iii) products remo ed from reaction system/ not in the system for lon" enou"h 1

[1#]

#. (a) Density = 1 0 " cm 1

)* 1 cm 3 (of $ater) $ei"hs 1 " 1

Sri Lankan School ?1


92/122

(b) (D. = 3 1 1 4*&- 5) 4 &7 (.C) calculated or correctly used (1)

48887&4+4+&'288

7 1, ,/1, ,, (k ) (1)orrect ans er ith some orking (2)

(c) (@ass used = 14 %& 1 4*6&7 5 ) 4&8 calculated or correctly used

(1)

@oles = 8&'78+&4

= 0 0 3, / 0 0 3' (1)

(d) (c)Answer to(b)Answer to

(1)

e " 82 -&8

-&4-

ne"ati e si"n and k mol 14 (1)ans$er correct to 3sf (1) 3

(e) (i) thanol aporises/e aporates (1) 1

(ii) #arbon/soot (1)!ncomplete com>'stion /insufficient o*y"en so reaction doesnot "o to completion (1)

[11]

. (a) (i) @"(s) + #u + (a ) @" + (a ) + #u(s)entities (1)state symbols (1)

(ii)

D S4r6 = D S! J@" + (a )K 1 D S! J#u + (a )Kentities includin" state symbols (1)arro$s (1);ess applied (1) 3



93/122

(b) (i) ' 04-8078 (1)= 3% 00 / 3 000 (1))* 3% / 3 kJ

(ii) 3% 00 / ,30000= 0 0%(13) (mol) 1

(iii) 1000 0 8&864 / 5 &*(2) cm 3

$LL) . from (i) and (ii) 1

(c) ;eat losses to s'rro'ndin s /container / throu"h container (1);eat capacity of chemicals not considered (1)!ncomplete reaction / mi*in" (1)

ny t$o reasonable points[11]

$. (a) (i) a particle / species /"roup $ith an unpaired electron /8G.. 1

(ii) 1

(iii) homolytic 1

(b) 2 and # 1

(c) (i) #1 + #; '

#; 3#l + ;#l 1(ii) + ' + ' + 1 * 5 1* %9 mol 14

( + 2 + ))* +' 1 *6 5 1* %9 mol 14

(2 + #)@ethod (1)ans$er $ith units (1)

(d) (i) - ' k mol 14 1

(ii) *othermic because a bond has been formed 1

(e) Eess endothermic (1)the bond is $eaker (1)

[11]

9. (a) (i) !t is the enthalpy / heat (ener"y) chan"e / e ol ed for theformation of 1 mo o% 'rea (1)

from its e ements (1)

in their standard states / at 1 atm and stated temperature R 4 5S (1) 3

Sri Lankan School ?#


94/122

(b) A ND D (i"nore units)

R(-333 0) + ( 1 2 -? )` 1 ( 2 '& ) + ( 1 * &-)`

5 ? 74 & + ' -&*

5 ? 4 2&* %9(3)

#orrect ans$er $ith some correct $orkin" (3)

#orrect ans$er alone (1)+ 13 4 k (2)8mittin" the 02 gi"es 146*&4 %9 (2)+ 1%4 1 k (1)!ncorrect application of ;ess ;s aw gi"es 1448'&6 %9 (2)+ 1 1 0' % k (1)!ncorrect ;ess ;s aw and omit 02 gi"es 148- &- %9 (1)+ 10, , k (0)

NO A ND D (i"nore units)

R(&3 ) + ( 12 -& )) 1 ((2 '& ) + ( 1 * &-)` (1)= - 41 0 + ' , 4= - '3 1 k (3)


#orrect ans$er alone (1)

+ '3 1 k (2)8mittin" the 02 gi"es 1 '6 & %9 (2)

" '% 3 k (1)

!ncorrect application of ;ess ;s aw gi"es 1 4'8 &* %9 (2)

" 1'03 4 k (1)

!ncorrect ;ess ;s aw and omit x2 gi"es 4 -6&4 %9 (1)

+ 13,% 1 k (0)[#]

$0. (a) species $ith a lone pair / pair of electrons (1)NO


95/122

(b) (i) mmonia / 7; 3 (in ethanol) (1)

heat (1) NO heat under reflu* (L+SS in a sealed tube

&! a temperature is quoted it must "e greater than 1::

in sealed tube / under pressure / concentrated (1)&! a pressure is quoted it must "e greater than 1 atm

#onditions are dependent on correct rea"ent

!f ammonia and an additional rea"ent maC (1) for t$o correct conditions3

(ii) #arbon-bromine bond stron"er / hi"her bond enthalpy than

carbon 1 iodine / a for C?#r is higher than C?I

/ NOR any e*tra e*planations in ol in" the alkyl "roups 1

(c) !dentify bonds broken and made (1)

e " ner"y in + '&' or + 33'0

AND ner"y out (-) &,& or (-) 3,3 (1)

ner"y needed to break bonds 1 energy released to ma%e bonds 5 7 (1)

e " #-! + '&' 1 7-7 5 + 7

or C?I + '8 1 - 2 5 + 7 (1)

#orrect e aluation dependent on use of 3& (1)

i e #-! = k mol 14 (1)


!f final ans$er is ne"ati e ma* (2)

!f 3& is on the $ron" sideB then 1,& ma* (-1,& (1) )

!f miss out 3&B then 14 maC 1 3

(d)

C C!

! % & & ' !

1[10]



96/122

$1. (a) for ener"y le el of product lo$er than reactant both labelled $ith species (1)

for acti ation hump D; (1)

for a bein" correctly marked (1)

$rro must not point do n ards for D bein" correctly marked (1)

e "

n t h a l p y

x t e n t o f r e a c t io n

R + ( )

( 2 ) R

2 2

a

'

(b) (i) starts at or near ori"in (not on * or y a*is) ske$ed distribution that isreasonably asymptotic to the *-a*is (1)

for uncat (must not be to the left of the peak) (1) 3for cat to the left of uncat (1) and still not to the /e!t o! the peak

R o o f A o l e c u l e s

e & g &

c a t

u n c a t

a

a

n e r g y

(ii) Gith the catalyst a "reater number/proportion of the molecules (1)

3his point must "e linked to the diagram in some ay,e g la"elled shading

ha e cat / sufficient ener"y to react (1)

and so more collisions result in reaction / more successfulcollisions (1) 3



97/122

(c) t , # no / fe$ molecules / collisions ha e a /sufficient ener"y to react (1)

t hi"her temperature the (a era"e) ener"y of the moleculesincreases (1)

t '00 # a "reater proportion of the molecules/collisionsha e ener"y "reater than/e ual to the acti ation ener"y (1) 3

[13]

$2. (a) c =[ ][ ]

(1)2

2'

'22

!C

MTMC!T

Startin amo'nts5

(1)====

mol8&molg4+/g-'!

mol72-&8molg47/g48C4

2

4'

'i i>ri'm amo'nts5- 4 7 0.#2 G H I 2.0 7 0. 1 2 mo (1)

2O 7 3.0 G 2.0 7 2.0 mo (1)-O 2 7 0.0 " H I 2.0 7 0. 00 mo (1)

2 7 2.0 mo ( i&en)

'i i>ri'm concentrations5

a>o&e &a 'es K 4 dm 3 (1) (mark conse 'ent :)

[- 4] 7 0.0312 mo dm83

[ 2O] 7 0. 00 mo dm 83

[-O 2] 7 0.12 mo dm83

[ 2] 7 0. 0 mo dm83

2

'

2eV2eV'

'eV2eV2

c-88&88 42-&8

-8&842-&8

M!TMCT

MTMC!T,

==

= 1 0 (or 1 or 1 00) (1) mol dm -& (1)

(b) D = (-34') 1 T(?67) + (2 0 1 2'2)M (2) 1 mark !or 2C 1 mar6 for signs and -alues

= + 1&& (1) k mol 14 3

177 scores


98/122


99/122

(ii) ie D; = '(40 ) + &( 12'4& ) 1'(1'7&4) (2)7 3&0 1 4'-8& + 4 '&' 5 1 *8-&7 %9 mol 14

= 1 *87 %9 mol 14 (1)

14 for incorrect significant figurescorrect use of ess cycle (1)correct use of multiples (1)conse uential ans$er $ith correct si"n and units (1) 3

[ ]

$4. (a) (i)

C R C R;

xoxoxo

xx

x

oo

o

ox

ox

oo

oo

1

(ii) 1 0 . (1).$o re"ions / areas of ne"ati e char"e / electrons re=e so as tobe as far apart as possible (1)

(b) ';#7 + ,8 ; 8 + '#8 + 7 1

(c) ark according to quality o! argument given

(o mark i! ans er e!!ectively re uotes the uestion 9ithout amplification

is chemically unsound

is nonsensical

$ns er must come to a conclusion and then look!or I&H R a sophisticated statement a"out dangers o! ( OR the use!ulness o! perspe-

(ot enough to say ?oC because it is -ery toxic but a de-eloped point such as Danger of an escape of /,? is an unacceptable ris6

to local residents 9ould score# :lternati-elyC an argument in fa-our of its use could be based on theexistence of ade uate ris6 assessment and or procedures for e-acuationin the e-ent of an emergency or need for a safer alternati-e to glass or other


100/122

(ii)

+ 4 4 8 ( % 9 m o l )( 1 )

: , , F K E r e - e r s e d a r r o 99 i t h 1 1 0 ) 6 * m o l %

1 4 1 4

1 1

$ F b e n u m e r i c a l " a l u e s

' 4 + ( C R )

+ 2 4 + 6 4 6 + ' 65 + 4 ' 8 ( % 9 m o l )

( 1 )

: , , F K E r e - e r s e d a r r o 99 i t h 1 ! 0 $ ) 6 * m o l %

(iii) (# 7) = 1'0 1 448 1 '45 + - (%9 mol 14) 1

[10]

$ . (a) nthalpy or heat chan"e or heat ener"y / released $hen 1 mol

of substance / element or compound (need to say both) (1)

is burned in e*cess o*y"en / completely / reacts completely (1)

at 1 atm pressure and specified temperature (1) 3

(b) D = D c(#) + D c(; ) - D c(#; 3#88;) (1) for this or e ui alent cycle dra$nT

D = ( 1 *'

) + (- &

) 1(1 6') (1)= -' & k mol 14 (1) 3

(c) ( nthalpy of) formation / D; f (1)

(d) correct orientation of ener"y le els / labelled (at least one) (1)

D; sho$n - number allo$ed (1)

reaction profile sho$in" + a (1)

Jif based on (b) ma* K

n t h a l p yC ( + ! )

C !

a c t i " a t i o n e n e r g y

2

2

[10]

Sri Lankan School 1::


101/122

$#. (a) (i) 9eaction is complete (1)

addition of coo er 7a8; causes temp to fall (1)

(ii) 0 0 cm3

(1) 1

(iii) 0 0 00 / 1000 (1) = 0 0'00 mol 1

(i ) 0 1 00 / 1000 (1) =0 0 00 mol 1

( ) 1 A (1) S3 "e consequential on orking in 4iii6 to 4iv6 1

( i) #u(8;) (1) onsequential provided that the ratio o! u to ) isa hole num"er 1

(b) (i) % # (or 5) (1) 1

(ii) = 1 10 / 1 1 k (1) onsequential on 4"64i6 1

(iii) D = 1 10 / 0 0 0 (1) ie method @ark conse uentially on (a)(i )and (b)(ii)

1 sign (1)

#orrect units (1) ( )

2 maC if numerical error ( )

&n !inal ans er 3

(c) 7o stirrin" / poor mi*in" (1)

Cpecified method of stirrin" or mi*in" e " ma"netic stirrer / s$irl cupbet$een additions (1)

or Colutions at different initial temperatures (1)

llo$ them to stabilise at room temperature (1)

Do not allo anything to do ith heat loss Do not allo more accuratethermometerT since the one specified is good enough#

[14]

Sri Lankan School 1:1


102/122

$ . (a) 488828

0 8&- 5 8&84 4

(b) ner"y chan"e = 0 0 '&4 0 27& 5 (24* &7 )

D > ( 1)84&8

7+&24*+

(1) 1228K $LL) .s! 14 4 , no units needed )* 0B000 (1)

[3]

$$. (a) (i) or$ard and re erse reactions occur at the same rate (1)so there is no chan"e in the proportions of reactants and products (1)

(ii) Proportion of ;! e*pected to become smaller (1)because reaction $ill respond to temperature increase by shiftin" in the

endothermic direction (1)(iii) 7o chan"e e*pected because catalysts affect only the rate at

$hich e uilibrium is attained 1

(b)

n e r g y

> r o g r e s s o f r e a c t i o n

2 l ( g )( r e a c t a n t s )

( g ) + l ( g )

( p r o d u c t s ) ( c a t a l y s e d )

( u n c a t a l y s e d )

a

a

2 2

Products at hi"her ener"y le el than reactants (1)

Eine "oin" up from reactants to peak (correspondin" to transition state)Bthen do$n to products (1)

Cecond line $ith lo$er peak representin" the catalysed reaction (1) cti ation ener"ies of uncatalysed and catalysed reactions correctly marked (1) '

[9]

$9. (a) @easure ( olume/ amount of "as) $ith a as s:rin e / in erted burette)* Eoss in mass $ith (top pan) >a ance89 Described titrimetric method (1)

at re"ular time inter als (1)



103/122

(b) (i) 9ate is proportional to (hydro"en pero*ide) concentration)* !nde* of (hydro"en pero*ide) concentration in rate e uation is 1 1

(ii) 9ate = k (1)J; 8 ((a ))K 1

(iii) @easure/ calculate/ find se eral/t$o hal-li es (1)

(#heck) half 1li"es are constant (1)

(c) (i)

R u m b e r o f m o l e c u l e sw i t h % i n e t i ce n e r g y K F F

F

n e r g y F

A

2

4

6eneral shape of . 1 "raph (1)

6eneral shape of . "raphA hi"her temperature peak lo$er and mo ed to the ri"ht (1)

#heck that "raphs start at Fero 1 penalise onceheck that graphs do not meet energy a-is penalise once#

(@any) more molecules $ith ener"y in e*cess of / min / a certain alue(1)#an be sho$n (as shadin") on the dia"ram

cti ation ener"y sho$n (1) '

Sri Lankan School 1:#


104/122

(ii)

I n ( r a t e )

4 / F / 4 8 , 1 1 4

*es correct $ith correct labels (1)

Censible Ccales as sho9n

"ut can "e shi!ted up/do n or right/le!t (1)

Points correct $ith best fittin" strai"ht line (1) 3

Sri Lankan School 1:.


105/122

(iii) 6radient = 1*688 (allow 1*288 to 148288) (1)a = 1 gradient / a = 1 & 4 0 gradient (1)

9= + 1 k mol 14 / + 1000 mol 14 $LL) %& to &orrect ans er, units, sign, 2SB (1) 3

[1#]

90. (a) nthalpy / heat (ener"y) chan"e on the neutralisation/ reaction of one mole of a mono>asic acid /hydro"en ions (by an alkali)or nthalpy / heat (ener"y) chan"e on the formation of one mole of $ater $hen an acid is neutralised8r

nthalpy chan"e per mole for reaction ;+ + 8;

- B

; 8 (1) 1

(b) = mcD. (1) other unambi"uous symbols/names= 100 0 '&4 0 7&*8 (1)= ' includin" units (1) 3onsequential on sensi"le chemistry in line 2 i e use o! 5: !or mass or tempin or data !or temperature, transposed4ma-26 &gnore sign o! ans er

$llo # or . signi!icant !igures

(c) '/0 0, (1)ans er !rom 4"6 : :5/allo ans er !rom 4"6 20= 1 -6&6 %9 mol 1 1 (1) accept 1 -6&7 2&! rong sign 4ma- 16&! rong units 4ma- 16

(d) nsures all acid reacts / neutralisation (of acid) 1completed / reaction (of acid) completed / all ; + reacted (1)

[ ]

91. (a) (i) nthalpy or heat chan"e / released $hen 1 mol of substance (1)is burned in e*cess o*y"en / completely (1)all substances in standard states (at a specified temp)/at a pressure of 1 atm (1) 3



106/122

(ii) Cuitable cycle (need not be labelled but if labelledBthese must be correct) (1) $orkin" (1) ans$er (1)

e & g & C + ! C ! ( C ! )

( C a r b o n )( C a r b o n m o n o x i d e )

C !c o m b

c o m b

f o r m2 2

2

4/

( 1 )

= -34' -(- 3) (1)= -111 (k mol 14) (1)0enalise 1 mark i! units incorrect 3

(iii) (some) #8 is al$ays produced in the reaction (1) 1

(i )

2 24/

( 1 )( n e r g y ) C ( + ! )

C !1

onsequential on 4a6 4ii6n " i! no ans er in4a6 4ii6, correct diagram can still score

(b) @ethane (and o*y"en) / reactants thermodynamically unstable

$ r t products (1)ust "e a comparisonCince reactants are at a hi"her ener"y le el (than products) (1)or reverse argument 9eactants / methaneB o*y"en kinetically stable (1)Due to hi"h acti ation ener"y (1) '&! no re!erence to methane in the ans er 4ma- #6

[12]



107/122

92. (a) Note 1 /ark !or improvement 1 /ark !or related reason in each case to /a 3/arks *eason must relate to improvement a- 2 !or improvement a- 2 !orreason

&mprovement insulate beaker / polystyrene cup / plastic cup / use lid (1)

*eason Pre ents / reduces heat loss or absorbs less heat (1)&mprovement ?se pipette / burette (1)

*eason @ore accurate (than measurin" cylinder) (1)

&mprovement @easure temperature for se eral minutes before the addition (1)

*eason llo$s more accurate alue for the initial temperature (1)

&mprovement @easure temperature more often (1)

*eason llo$s for better e*trapolation / more accuratetemperature chan"e from "raph (1)

&mprovement 9ead thermometer to 1 dp / use more precisethermometer/ di"ital thermometer (1)

*eason 6i es more accurate temperature chan"e (1)

&mprovement Ctir mi*ture (1)

*eason nsure e en temperature / reaction faster less heat loss$ith time (1)

&mprovement ?se finely di ided iron / smaller pieces (1)

*eason 9eaction faster less heat loss $ith time (1)7ot speeds up alone '

(b) (i) ;eat chan"e = ,0 0 0 '&4 0 4-&295 -8&8 0 '&4 0 4-&2 / 4888%95 &4 %9 or 4 89 (1)&gnore sig !ig $llo mark i! units omitted 1&! units quoted "ut rong eg # 18 % score :

(ii) 7o of mols of copper sulphate = ,0 0 0 8&-88 / 4888

5 8&82- (1) 1

(iii) nthalpy chan"e per mol = 3 1 / 0 , = 1426%9 (1)ne"ati e si"n (1) stand aloneconsequential on 4i6 and 4ii6ma- . sig !ig and ans er must "e in k% mol M1 even i! units omitted

[$]



108/122

93. (a) (i) uation (1)

+ ! + 2 !2 22

( 1 )

! !

! !

3here are several ays o! ans ering the rest o! this section $lternative 1 3

= + '%: (1).his is positi eB therefore reaction feasible (1)

$lternative 2 2oth alues are positi eB so sum of is positi e (1).herefore reaction is feasible (1)

(ii)

R u m b e r /f r a c t i o n o f m o l e c u l e s

( w i t he n e r g y )

c a ta a ( )

@a*$ell-2oltFmann "raph - 1 mark for shape of "raph1 mark for correct a*esplotted and labelled1 mark for a and a cat

Do not a ard third mark i! either o! the + values is on le!t hand side o! ma- on hump

C= anationarea under "raph to ri"ht of cat N area to ri"ht of a (1)

"reater number/ fraction of molecules or particles ha e enou"hener"y to react on collision or "reater number of effecti e / ,successful collisions (1)&! dra t o graphs sho ing di!!erent temperature ignore

(iii) .he reactant/ 1B'-dihydro*ybenFene (and the product/ uinone both)ha e delocalised rin" (or resonance) systems/ or describeddelocalisation (or resonance) (1)these a era"e bond ener"ies are for localised bonds / do notapply to benFene rin" compounds / compounds $ith delocalisedor resonance systems (1)



109/122

(b) 0 dm 3 o*y"en is 0/ ' = 0 33 mol (1)amount pero*ide in 1 dm 3 = 0 33 mol 0 2 (1) = 1 &% molmass 1 &% mol 0 ' g mol -1 = ,% / ,& & / ,& % / ,& " (dm 1 ) (1) 3

(c) (i) ; 8 8 + ; + + e - (1) 1

(ii) @n8 '- + &; + + , ; 8 @n + + ; 8 + ,8

species on correct side of e uation (1) balance (1)@n8 '

1 + ; + + ,e 1 @n + + '; 8 &! the overall equation, isnot correct allo 1 mark !or this equation i! correct ignore

(iii) ;i"her concentration increases collision fre uency / more collisionsper unit of time (1)t ere%ore causes increase in reaction rate (1)ore success!ul collisions there!ore !aster gets 1 mark 4no re!erence to higher concentration6

[1$]

94. (a) (i) nt a =:6 eat c an e for formation of 1 mo e of acompound (1)from its e ements (1)in their standard states / or stated temperature of 4 5( , #) and 1 atm (or suitable unit) (1) 3

(ii) = -&0 ' - (, 3-3& ) (1)= -%& , (5O mol81) (1)

(iii) ne"ati e si"n means reaction e*othermic/"i es out heat (1)if no ans$er "i en to part (ii) must "i e "eneral e*planationthat ne"ati e means e*othermic and positi e means

endothermic reaction 1

(b) ner"y in = (&1 + 3&&) = 4% (1)ner"y out = 3' + '1 + %& = 103& (1)ner"y chan"e = 4% 1 48 7 5 ?- (1) conse uential&! candidates choose to include the !our M "onds the a"ove!igures are 2727, 278. and M58 3

Sri Lankan School 1:?


110/122

(c) A&era e alues from many compounds used in bondenthalpies (1)Act'a &a 'es for these compounds probably sli"htly different/ orB calculation in (a) (ii) uses real / actual / e*perimental/standard/ alues (1)

n " do not accept arguments "ased on error [11]

9 . (a) Eattice ner"yA

enthalpy or heat ener"y released (could mention theprocess is e*othermic or alue ne"ati e) (1)

a $hen "aseous ions (1)

(come to"ether to) form / mole solid / crystal / lattice (1)"ut not su"stance

i! equation given could get state marks and energy changemarks i! D sho n 3

nthalpy of tomisationA

heat ener"y chan"e for the formation of one mole of "aseous atoms (1)

from an element in its standard state (1)

not standard conditionsi! state or imply e-othermic ma- 1

(b) (i) correct step sho$n (1) must identi!y change 1

(ii) +1,0 + %3& + 1',0 + ( 0 424) + 7'2 5 2285 2'* + 2x (1)* = % %* = 1 7 Y 4 (1) si n &itan " M929 scores 1, 303 scores 1C M7:7 scores :


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answers for energetic questions