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1. Which of these diagrams correctly represents an endothermic reaction?

(Total 1 mark)

2. This question is about methanol and the energy changes that accompany some of its reactions.

(a) Complete the diagram (using dots and crosses) to show the bonding in methanol, CH!H.

"ou should show outer electrons only.

(2)

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(b) The Hess cycle below can be used to calculate the standard enthalpy change of

combustion of methanol, using standard enthalpy changes of formation.

(i) Complete the cycle by filling in the empty bo#.(2)

(ii) $efine the term of a compound, ma%ing clear the meaning of standardin this

conte#t.

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(iii) &se your cycle and the data below to calculate the standard enthalpy change of

combustion of methanol, 'Hc

'Hf

%* mol+

C!-(g) +./

H-!(l) +-0/.0

CH!H(l) +-.

(2)

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(c) 1n e#periment was carried out, using the apparatus below, to estimate the standard

enthalpy change of combustion of methanol.

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1fter burning the methanol for a few minutes, the temperature of water in the bea%er had

risen by -2.3 4C and the mass of methanol burnt was 2.050 g.

(i) Calculate the amount of energy transferred to the water.

6nergy transferred (*) 7 mass of water 8 5.0 8 temperature change(1)

(ii) Calculate the number of moles of methanol, CH!H, burnt during the e#periment.

(1)

(iii) &se your answers to (c)(i) and (ii) to calculate the e#perimental 9alue for the

standard enthalpy change of combustion. :nclude a sign and units in your answer,

which should be gi9en to threesignificant figures.(1)

(i9) Compare your answers to (b)(iii) and (c)(iii) and gi9e TW! reasons to e#plain any

differences.

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(Total 14 marks)

3. Which of the following is true for the e#othermic reaction shown below?

;g(s) < -HCl(aq) = ;gCl-(aq) < H-(g)

A 'H positi9e

B 'Ssurroundings positi9e

C 'Ssystem negati9e

D 'Stotal negati9e

(Total 1 mark)

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4. (a) Crystals of hydrated cobalt(::) chloride, CoCl-.>H-!, lose water when they are heated,

forming anhydrous cobalt(::) chloride, CoCl-.

CoCl-.>H-!(s) = CoCl-(s) < >H-!(l)

(i) Calculate the entropy change of the system, 'S

system, at -0 . :nclude a sign and

units in your answer. "ou will need to refer to your data boo%let.(2)

(ii) 6#plain whether the sign of your answer to (a)(i) is as e#pected from the equation

for the reaction.

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(iii) The standard enthalpy change for the reaction, 'H

, is


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(b) 1 student attempted to measure the enthalpy change of solution of anhydrous cobalt(::)

chloride by adding -.22 g of cobalt(::) chloride to /2.2 cmof water in a well@insulated

container. 1 temperature rise of ./ 4C was recorded.

The student used a balance which reads to 2.2g, a /2.2 cm

pipette, and a thermometerwhich can be read to 2.-/ 4C.

(i) Which measuring instrument should be changed to gi9e a result which is closer to

the accepted 9alue? *ustify your answer.

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(ii) Auggest !B6 otherchange the student could ma%e to gi9e a result which is closer

to the accepted 9alue. *ustify your suggestion.

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(c) The lattice energies of magnesium chloride, ;gCl-, calcium chloride, CaCl-, and

strontium chloride, ArCl-are shown in the table below.

Chloride attice energy%* mol+

;gCl- +-/->

CaCl- +--/0

ArCl- +-/>

(i) &se data on ionic radii, from your data boo%let, to e#plain the trend in these 9alues.

6stimate a 9alue for the lattice energy of cobalt(::) chloride, gi9ing !B6 piece of

data to Dustify your estimate.

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(ii) 6#plain how lattice energy 9alues, together with other data, can be used to predict

the solubility of ionic compounds.

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(d) Cobalt forms another chloride, CoCl, but scientists predict that ;gClcannot be made.

Auggest a reason for this.

"ou should consider the enthalpy changes in the Eorn@Haber cycle, which pro9ide

e9idence about why cobalt(:::) chloride is %nown but magnesium(:::) chloride is not.

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(Total 20 marks)

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5. Which equation represents the reaction for which the enthalpy change is the standard enthalpy

change of formation, 'HfF, of sodium nitrate, BaB!?

A -Ba(s) < B-(g) < !-(g) = -BaB!(s)

B Ba(s) < GB-(g) < G!-(g) = BaB!(s)

C Ba(s) < B(g) < !(g) = BaB!(s)

D Ba(g) < GB-(g) < G!-(g) = BaB!(g)

(Total 1 mark)

6. Which equation represents the reaction for which the enthalpy change, 'H, is the mean bondenthalpy of the C+H bond?

A CH5(g) = C(g) < H(g)

B CH5(g) = C(s) < -H-(g)

C CH5(g) = C(g) < 5H(g)

D CH5(g) = C(g) < -H-(g)

(Total 1 mark)

7. ;agnesium chloride can be made by reacting solid magnesium carbonate, ;gC!, with dilute

hydrochloric acid.

(a) Write an equation for the reaction, including state symbols.(2)

(b) Ii9e TW! obser9ations you would ma%e when the reaction is ta%ing place.

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(c) :n an e#periment to ma%e crystals of hydrated magnesium chloride, ;gCl-.>H-!,

magnesium carbonate was added to -/ cmof hydrochloric acid with concentration -.2

mol dm+

. The molar mass of magnesium carbonate is 05. g mol+

.

(i) How many moles of acid are used in the reaction?(1)

(ii) What mass of magnesium carbonate, in grams, reacts with this amount of acid?(1)

(iii) Auggest why slightly more than this mass of magnesium carbonate is used in

practice.

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(i9) How would you separate the magnesium chloride solution from the reaction

mi#ture in (iii)?

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(1)

(9) The magnesium chloride solution was left to crystallise. The crystals were

separated and dried carefully. 1 sample of .3/g of hydrated crystals, ;gCl-.>H-!,

which ha9e molar mass -2. g mol+

, was obtained. Calculate the percentage

yield of this reaction.(2)

(9i) Ii9e !B6 reason why the yield of crystals is less than 22J, e9en when pure

compounds are used in the preparation.

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(d) attice energies can be measured using the Eorn@Haber cycle, or calculated from

electrostatic theory. attice energies of magnesium chloride and magnesium iodide are

shown below

Aaltattice energy fromEorn@Haber cycle using

e#perimental data

%* mol+

attice energy fromelectrostatic theory

%* mol+

;gCl- +-/-> +-->

;g:- +--3 +55

(i) What does this data indicate about the bonding in magnesium chloride?

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(ii) 6#plain why there is a greater difference between the e#perimental (Eorn@Haber)

and theoretical lattice energies for magnesium iodide, ;g:-, compared with

magnesium chloride.

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(e) Elood plasma typically contains -2 parts per million (ppm) of magnesium, by mass.

(i) Calculate the mass of magnesium, in grams, present in 22 g of plasma.(1)

(ii) ;agnesium chloride can be used as a supplement in the diet to treat patients withlow amounts of magnesium in the blood. Auggest !B6 property which ma%es it

more suitable for this purpose than magnesium carbonate.

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(Total 16 marks)

8. This question is about he#ane, C>H5, and he#@@ene, C>H-.

(a) What test would you use to distinguish between he#ane and he#@@ene? Ii9e the results

of the test for each substance.

TestK ............................................................................................................................

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Lesult with he#aneK ....................................................................................................

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Lesult with he#@@eneK ................................................................................................

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(b) He#@@ene has a number of isomers, including two stereoisomers of he#@-@ene.

(i) Complete the formula to show the structure ofE@he#@-@ene.

(1)

(ii) 6#plain why stereoisomerism can occur in al%enes, and why he#@-@ene has

stereoisomers but he#@@ene does not.

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(c) The enthalpy change of combustion of he#ane was measured using a spirit burner to heat

a %nown mass of water in a calorimeter. The temperature rise of the water was measured.

The results of the e#periment are shown below.

;ass of he#ane burnt 2.- g

;ass of water in calorimeter /2 g:nitial temperature of water -- 4C

Minal temperature of water >0 4C

The specific heat capacity of water is 5.0 * g+

4C+

.

(i) Calculate the energy in Doules produced by burning the he#ane. &se thee#pression

energy transferred 7 mass 8 specific heat capacity 8 temperature change.(1)

(ii) Calculate the enthalpy change of combustion of he#ane. The mass of mole of

he#ane is 0> g.

Ii9e your answer to TW! significant figures. :nclude a sign and units in your

answer.(3)

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(iii) The 9alue for the enthalpy change of combustion in this e#periment is different

from the 9alue gi9en in data boo%s. Auggest TW! reasons for this difference.

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(i9) 1 student suggested that the results would be more accurate if a thermometer

which read to 2.4C was used. 6#plain why this would notimpro9e the accuracy

of the result. 1 calculation is notrequired.

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(d) He#@@ene can be con9erted to he#ane in the following reaction.

C>H-(l) < H-(g) = C>H5(l)

(i) What catalyst is used in this reaction?

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(ii) The enthalpy change of this reaction 'Hreactioncan be calculated from the following

enthalpy changes of combustion.

Aubstance6nthalpy change of combustion

%* mol+

He#@@ene, C>H- +522

Hydrogen, H- +-0>

He#ane, C>H5 +5>

Complete the Hess cycle by adding labelled arrows. &se your cycle to calculate the

enthalpy change 'Hreaction.

(3)

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(iii) The enthalpy change for the reaction of some other al%enes with hydrogen is

shown below.

LeactionAtandard enthalpy change

%* mol+

CH>< H-= CH0 +522

C5H0< H-= C5H2 +-0>

C/H2< H-= C/H- +5>

6#plain why the 9alues are so similar.

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(Total 17 marks)

9. 1t 22 4C, pure water has a pH of >, whereas at -/ 4C it has a pH of 3. This is because

A the dissociation of water is endothermic, so the concentration of hydrogen ions is lower at

22 4C than it is at -/ 4C.

B the dissociation of water is e#othermic, so the concentration of hydrogen ions is lower at

22 4C than it is at -/ 4C.

C the dissociation of water is endothermic, so the concentration of hydrogen ions is higher

at 22 4C than it is at -/ 4C.

D at 22 4C, water has a higher concentration of hydrogen ions than of hydro#ide ions.(Total 1 mark)

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10. Aome mean bond enthalpy 9alues are gi9en in the table below.

Eond ;ean bond enthalpy %* mol+

HNH

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12. The Eorn@Haber cycle for the formation of sodium chloride from sodium and chlorine may be

represented by a series of steps labelled Ato as shown.

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(a) (i) Complete the table below by adding the letters Ato ne#t to the corresponding

energy changes.

6nergy change etter 'H

%* mol+

attice energy for sodium chloride +33/

6nthalpy change of atomiOation of sodium


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(b) attice energies can be calculated from electrostatic theory (theoretical 9alues) as well as

by Eorn@Haber cycles (e#perimental 9alues).

Compound 6#perimental lattice energy

%* mol+

Theoretical lattice energy

%* mol+

BaCl +332 +3>>

1gl +00 +330

(i) Comment on the fact that there is close agreement between the 9alues for sodium

chloride, BaCl.

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(ii) 6#plain, in terms of chemical bonding, why the e#perimental 9alue for sil9er

iodide, 1g:, is more e#othermic than the 9alue calculated theoretically for the same

compound.

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(c) Auggest why the first ioniOation energies of the Iroup elements decrease down the

group.

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(Total 10 marks)

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13. Propanone, CH>!, undergoes complete combustion to form carbon dio#ide and water.

CH>!(l) < 5!-(g) = C!-(g) < H-!(l)

(a) :n an e#periment to calculate the enthalpy change of combustion for propanone, -.2 g of

propanone was burned completely in o#ygen.

The heat energy from this combustion raised the temperature of -22 g of water from -2.-

4C to 30.5 4C.

The specific heat capacity of water is 5.0 * g+

4C+

.

(i) Calculate the number of moles of propanone present in -.2 g.

QThe molar mass of propanone is /0 g mol+

.R

(1)

(ii) &se the e#pression

energy transferred (*) 7 mass 8 capacity

heatspecific

8 change

etemperatur

to calculate the heat energy transferred to raise the temperature of -22 g of water

from -2.- 4C to 30.5 4C.(2)

(iii) &se your answers to (a)(i) and (ii) to calculate a 9alue for the enthalpy change of

combustion of propanone. Ii9e your answer to threesignificant figures and

include a sign and units.(3)

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(b) :n another e#periment, the enthalpy change of combustion for butanone, C5H0!, was

found to be +22 %* mol+

.

1 $ata Eoo% 9alue for the standard enthalpy change of combustion for butanone is +-552

%* mol+

.

(i) Auggest a reason why the 9alue obtained in the e#periment is so different from the

$ata Eoo% 9alue.

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(ii) This $ata Eoo% 9alue (+-552 %* mol+

) refers to the following equation.

C5H0!(l) < -,,

!-(g) = 5C!-(g) < 5H-!(l)

How would the 9alue be different if it referred to the formation of water in the

!aseo"sstate? *ustify your answer.

$ifference.........................................................................................................

*ustification.......................................................................................................

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(c) Atandard enthalpy changes of combustion can be used to calculate the standard enthalpy

change of formation of a compound.

(i) $efine the term standard enthal#$ %han!e o& &ormat'on, ma%ing clear the

meaning of standardin this conte#t.

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(ii) &se the standard enthalpy changes of combustion, 'Hc

, gi9en in the table below

to find the standard enthalpy change of formation for ethanoic acid, CHC!!H, in

%* mol+

.

Aubstance 'Hc

%* mol+

C(s, graphite) +5

H-(g) +-0>

CHC!!H(l) +032

-C(s, graphite) < -H-(g) < !-(g) = CHC!!H(l)

(3)

(Total 15 marks)

14. :n the reaction profile below, which energy change would alter if a catalyst was added to the

reaction?

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A

B

C

D(Total 1 mark)

15. Which equation represents the reaction for which the enthalpy change is the lattice energy of

sodium fluoride, BaM?

A Ba(s) < GM-(g) = BaM(s)

B Ba(g) < M(g) = BaM(s)

C Ba.0

H-A (g) +-2.>

H-! (l) +-0/.0

(2)

(Total 7 marks)

27. This question is about ammonia, BH, which is produced as shown in the following equation.

B-(g) < H-(g) -BH(g)

(a) &se o#idation numbers to e#plain why this is a redo# reaction.

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(b) (i) &se the a9erage (mean) bond enthalpy data to calculate a 9alue for the enthalpy

change for this reaction. "ou are reminded to show all your wor%ing.

Eond19erage bond enthalpy

%* mol

+

B[B 55

H\H 5>

B\H 00

(3)

(ii) The actual standard enthalpy change for this reaction is +- %* mol+

. 6#plain why

the 9alue you calculated in (b)(i) is not the same as this.

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(iii) 1t room temperature, a mi#ture of nitrogen and hydrogen is thermodynamically

unstable with respect to ammonia, but is %inetically stable.

&se the data in (b)(i) and (ii) to help you e#plain why this mi#ture is

thermodynamically unstable

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%inetically stable

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(c) The manufacturer of ammonia would li%e to achie9e a high rate of reaction and a high

equilibrium yield of product.

(i) Atate and e#plain, in terms of collision theory, TW! ways to increase the rate of

the reaction. 1n increase in pressure does not alter the rate in this process.

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(ii) Atate and e#plain TW! ways to increase the equilibrium yield of ammonia.

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(Total 19 marks)

28. The enthalpy change for the reaction between aqueous sodium hydro#ide solution and aqueous

hydrochloric acid was determined by the following methodK

1queous hydrochloric acid was titrated against -/.2 cmof ./2 mol dm

+aqueous

sodium hydro#ide solution using a suitable indicator. The mean (or a9erage) titre was

--.3/ cm.

-/.2 cmof the sodium hydro#ide solution was carefully measured into a polystyrene cup

and --.3/ cm

of the hydrochloric acid was transferred to a clean dry bea%er.Eoth solutions were allowed to stand for fi9e minutes before their temperatures were

noted.

The hydrochloric acid was then added to the sodium hydro#ide solution, the mi#ture

stirred thoroughly and the highest temperature noted.

The e#periment was repeated three times gi9ing an a9erage temperature change of


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(a) (i) Calculate the heat produced in the reaction, in Doules.

&se the appro#imations that the density of the final solution is .22 g cm+

and its

specific heat capacity is 5.0 * g+

+

.

(2)

(ii) Calculate the enthalpy change for the reaction, in %* mol+

.

(3)

(b) Atate !B6 assumption made when calculating this enthalpy change, other than those

stated in (a)(i).

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(Total 6 marks)

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29. The Eorn@Haber cycle below represents the enthalpy changes when calcium hydride, CaH-, is

formed from its elements.

H /

C a H ( s )-

C a - < ( g ) < - e + < - H ( g )

C a - < ( g ) < - e + < H - ( g )

C a ( g ) < H - ( g )

C a ( s ) < H - ( g )

C a - < ( g ) < - H + ( g )

H ,

H -

H

H 5

' H >

(a) Write down in terms of one of the symbols 'Hto 'H>

(i) the lattice energy of calcium hydride ................................................................(1)

(ii) the first electron affinity of hydrogen ................................................................(1)

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(b) &se the data below to calculate the standard enthalpy of formation of calcium hydride,

CaH-(s).

9alue

%* mol+

enthalpy of atomisation of calcium


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30. Two e#periments were carried out in order to calculate the enthalpy change of formation of

magnesium carbonate, ;gC!.

1 Hess cycle for these reactions is shown below.

H

- + # e r ' m e n t 1

; g

Temp 4C -.2 -.2 -/. -/. -5. -5.0 -5.3

(i) How many moles of magnesium were used in this e#periment?

&se the Periodic Table as a source of data.

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(ii) The initial concentration of the hydrochloric acid was -.22 mol dm+

.

Calculate the number of moles of hydrochloric acid at the start and hence the

number remaining at the end of the e#periment.

(3)

(iii) Plot the graph of temperature against time.

(2)

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(i9) Calculate the energy change in this e#periment assuming the temperature rise is

5./ 4C. &se the e#pression

6nergy change (*) 7 5.- 8 mass of solution 8 temperature change

Q1ssume that cmof solution has a mass of gR

(1)

(9) &se your answer to (i9) to calculate ZHfor one mole of magnesium reacting with

hydrochloric acid. :nclude a sign and units in your answer.

(2)

(9i) Auggest why a temperature rise of 5./ 4C was used in the calculation in (i9).

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(c) -.- g of magnesium carbonate was added to 22 cmof the same acid in -+#er'ment 2.

The temperature changed from -.2 4C to -./ 4C resulting in an energy change of

.2/ %*.

(i) Calculate the mass of one mole of magnesium carbonate, ;gC!and hence the

number of moles of magnesium carbonate used in this e#periment.


(2)

(ii) &sing the method in part (b)(9), calculate ZH.

(1)

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(d) &sing your answers to (b)(9) and (c)(ii), calculate the enthalpy change of formation, ZHf,

of magnesium carbonate, ;gC!.

:nclude a sign and units in your answer.

(2)

(e) Why is it impossible to measure ZHfof ;gC!(s) directly?

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(Total 18 marks)

31. Calculate the standard enthalpy change of formation of gaseous silicon tetrachloride,

'H

fQAiCl5(g)R.

"our answer should include a sign and units.

&se the Hess cycle below and the following data at -0 .

oatH QAi(s)R 7 %* mol

+

oatH QGCl-R 7


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32. (a) When e#cess chlorine and methane are mi#ed at room temperature and pressure no

reaction ta%es place but when ultra9iolet light is shone into the mi#ture an e#plosion

occurs, producing carbon and hydrogen chloride.

CH5(g) < -Cl-(g)u9

C(s) < 5HCl(g) ZH 7 +- %* mol

+

Calculate the mass of methane needed to produce 222 %* of energy.

(2)

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(b) $raw a laelled reaction profile for the reaction between methane and chlorine and use it

to e#plain why the reaction does not ta%e place unless ultra9iolet light is present.

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

6 n t h a l p y

6#planation

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(Total 7 marks)

33. (a) $efine the term standard enthal#$ o& %om"st'on.

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(b) The following standard enthalpies of combustion are needed to calculate the standard

enthalpy of formation of ethanol, C-H/!H.

/"stan%e/tandard enthal#$ o&

%om"st'on k mol1

carbon, C (s, graphite) +5

hydrogen, H-(g) +-0>

ethanol, C-H/!H (l) +3

(i) Complete the HessUs aw cycle by filling in the bo# and labelling the arrows with

the enthalpy changes.

H

- C ( s ) < H - ( g ) < G ! - ( g ) C - /H ! H ( l ) < ! - ( g )

. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . < . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

f

(3)

(ii) &se your HessUs aw cycle to calculate the standard enthalpy of formation of

ethanol.

(2)

(Total 8 marks)

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34. The apparatus used and the recordings made by a student, carrying out an e#periment to

determine the enthalpy of combustion of methanol, are shown below.

D'a!ram

t h e r m o m e t e r

b e a % e r

w a t e r

m e t h a n o l

s p i r i t l a m p

es"lts

;olar mass (methanol) 7 - g mol+

Yolume of water in bea%er 7 /2 cm

;ass of water in bea%er 7 /2 g

Weighings

Apirit lamp < methanol before combustion 7 >.30 g

Apirit lamp < methanol after combustion 7 >.55 g

Temperatures

Water before heating 7 --.2 4C

Water after heating 7 5./ 4C

Apecific heat capacity of water 7 5.0 * g+

4C+

serat'ons

When the spirit lamp was being weighed its mass was continually falling.

1 blac% substance formed on the bottom of the bea%er as the methanol burned.

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(a) (i) Calculate the amount (moles) of methanol, CH!H, burned.

(2)

(ii) Calculate the heat gained by the water. Ii9e your answer in %*.

(2)

(iii) &se your 9alues from (i) and (ii) to calculate the enthalpy of combustion of

methanol in %* mol+

. :nclude a sign with your answer.

ZH 7 ........................................ %* mol+

(2)

(b) (i) The thermometer used in the e#periment can be read to an accuracy of ]2./ 4C.

Calculate the percentage error in the temperature change.

(1)

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(ii) Calculate the ma#imum temperature change that could ha9e occurred during the

e#periment.

(1)

(c) (i) Ii9e a reason why the mass of the spirit lamp fell as it was being weighed.

...........................................................................................................................

...........................................................................................................................

(1)

(ii) Auggest the identity of the blac% substance that forms on the bea%er. Atate the effect

on the 9alue of the enthalpy of combustion obtained.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

(2)(Total 11 marks)

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35. (a) 1n incomplete Eorn@Haber cycle for the formation of magnesium o#ide, ;g!, from its

constituent elements is shown below. 1ll numerical 9alues are in %* mol+

.

l a t t i c e e n e r g y o f m a g n e s i u m o # i d e

f i r s t p l u s s e c o n d

i o n i s a t i o n e n e r g y o f

m a g n e s i u m 7 < - , 0 >

e n t h a l p y o f a t o m i s a t i o n

o f o # y g e n 7 < - 5

; g - < ( g ) < ! ( g ) < - e +

- 2 -

H 7 < , / 2

; g ( g ) < ,- ! ( g )-

; g ( s ) < ,- ! ( g )-

; g ! ( s )

H 7 < > / 3

,

-

(i) Complete the empty bo# on the cycle by writing in the formulae of the missing

species. Atate symbols are required.(1)

(ii) :dentify each of the following enthalpy changes by nameK

'H ....................................................................................................................

'H- ....................................................................................................................

'H ....................................................................................................................

(3)

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(iii) &se the Eorn@Haber cycle to calculate the lattice energy of magnesium o#ide.

(2)

(b) ;agnesium iodide is another compound of magnesium. The radius of the magnesium ionis 2.23- nm, whereas the radius of the iodide ion is much larger and is 2.-/ nm.

(i) $escribe the effect that the magnesium ion has on an iodide ion ne#t to it in the

magnesium iodide lattice.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(1)

(ii) What TW! quantities must be %nown about the ions in a compound in order to

calculate a theoretical lattice energy?

...........................................................................................................................

...........................................................................................................................(2)

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(iii) Auggest how the 9alue of the theoretical lattice energy would compare with the

e#perimental 9alue from a Eorn@Haber Cycle for magnesium iodide.

Ii9e a reason for your answer.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(2)

(Total 11 marks)

36. (i) $efine the term enthal#$ o& h$drat'on, Hh$d, of an ion.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................(2)

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(ii) The table below gi9es some information about the sulphates of the Iroup - elements

magnesium and barium.

s"l#hate latt'%e ener!$

k mol1

h$drat'on

enthal#$ o& %at'on

k mol1

sol"'l't$

mol dm3

;gA!5 +-035 +-2 .0

EaA!5 +-35 +>2 .5 8 2+>

&se the lattice energy and hydration enthalpy 9alues to e#plain the difference in the

solubility of the two salts.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................(4)

(Total 6 marks)

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37. 1mmonia can be o#idised with o#ygen in two ways.

Leaction :K 5BH(g) < /!-(g) = 5B!(g) < >H-!(g),

Leaction ::K 5BH(g) < !-(g) = -B-(g) < >H-!(g)

The first reaction is used in the con9ersion of ammonia to nitric acid.

(a) $efine the term enthal#$ o& &ormat'on.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................(2)

(b) The following enthalpies of formation are needed for this question.

Hf k mol1

BH(g) + 5>.

B!(g) < 2.-

H-!(g) + -5-

(i) Calculate the enthalpy change for Leaction :.

(2)

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(ii) Calculate the enthalpy change for Leaction ::.

(1)

(c) Whene9er ammonia is o#idised, the two reactions occur at the same timeK they are

competing reactions.

(i) Auggest, with a reason, which reaction you would e#pect to be more li%ely

thermod$nam'%all$.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(1)

(ii) 6#plain how the use of a catalyst can fa9our Leaction : o9er Leaction ::.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(2)

(d) :n the nitration of benOene, a mi#ture of concentrated nitric and sulphuric acids is used ata temperature not e#ceeding // 4C.

(i) What is the reason for using sulphuric as well as nitric acid? Aupport your answer

with an equation.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(2)

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(ii) !n the basis of your answer to (d)(i), which of nitric and sulphuric acid is the

stronger acid? Ii9e a reason.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(1)

(iii) Ii9e the mechanism for the nitration of benOene.

(3)

(i9) :f the temperature of the reaction mi#ture rises much abo9e // 4C, other

compounds are formed in addition to nitrobenOene.

Auggest the structural formulae of !B6 of these compounds.

(1)

(9) 6#plain, in terms of structure and energetics, why benOene usually reacts 9ia

substitution rather than addition.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(3)

(Total 18 marks)

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38. Calcium hydro#ide decomposes on strong heating to form calcium o#ide and water.

Ca(!H)-(s) = Ca!(s) < H-!(l)

Two samples of %al%'"m h$dro+'de were ta%en, each weighing e#actly .22 g.

The first sample was cautiously added to -/.2 cmof dilute hydrochloric acid contained in a

glass bea%er. The temperature rise was measured and found to be >./ 4C.

The other sample was heated for some time. :t was then allowed to cool and then added to

another -/.2 cm portion of hydrochloric acid as before. :n this case the temperature rose by

-/./ 4C.

:n both cases, the acid used was an e#cess.

(a) (i) Calculate the energy produced by the reaction of each solid with the acid.

&se the relationship

6nergy produced 7 mass of solution 8 5.- 8 temperature rise

* g * 4C+

g+

"ou may assume that .2 cmof solution has a mass of .2 g. :gnore the mass of

the solid.

Mor the solid calcium hydro#ide

Mor the solid calcium o#ide

(1)

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(ii) How many moles of calcium hydro#ide were used in each e#periment?

Q;olar mass of Ca(!H)-7 35.2 g mol+

R

(1)

(iii) &sing your answers to (a)(i) and (ii), calculate the enthalpy changes for each

reaction.

Ii9e your answers to t,o s'!n'&'%ant &'!"res. :nclude the sign and units for each

answer.

Mor the solid calcium hydro#ide, 'H

Mor the solid calcium o#ide, 'H-

(2)

(b) 1 Hess cycle for all these reactions is shown below.

C a ( ! H ) - ( s ) C a ! ( s ) < H - ! ( l )

C a C l - ( a q ) < - H - ! ( l )

H r e a c t i o n

H , H -

- H C l ( a q ) - H C l ( a q )

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(i) &se this Hess cycle and your answers in (a)(iii) to calculate 'Hreaction. :nclude a

sign and units.

(2)

(ii) 1part from the appro#imations in9ol9ed in using the equation gi9en in (a)(i), gi9e

TW! other potential sources of error which are li%ely to affect the accuracy of theresults.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(2)

(iii) Auggest why 'Hreactionis difficult to determine directly by e#periment.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(1)

(Total 9 marks)

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39. (a) $efine the term standard enthal#$ o& &ormat'on.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................(3)

(b) :n the Haber process, ammonia is manufactured from nitrogen and hydrogen as shown in

the equation.

B-(g) < H-(g) -BH(g)

(i) &se the bond enthalpies below to calculate the standard enthalpy of formation of

ammonia.

Bond Bond enthal#$ k mol1

B[B in B-


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(ii) $raw a labelled enthalpy le9el diagram for the formation of ammonia in the Haber

process.

6 n t h a l p y

(2)

(iii) Atate the temperature used in the Haber process and e#plain in terms of the rate of

reaction and position of equilibrium, why this temperature is chosen.

Temperature .......................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(3)

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(i9) :dentify the catalyst used in the Haber process and state what effect, if any, it has

on the equilibrium yield of ammonia.

Catalyst ................................................................

6ffect on yield ...................................................................................................(2)

(9) 6#plain why it is necessary to use a catalyst in this process.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(1)

(c) The pressure used in the Haber process is -/2 atmospheres.

(i) Atate and e#plain an ad9antage of increasing the pressure to 222 atmospheres.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(2)

(ii) Auggest a disad9antage of using a pressure of 222 atmospheres.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(1)

(Total 18 marks)

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40. The enthalpy change for the reaction of anhydrous aluminium chloride, 1lCl, with water can be

found as followsK

1dd about 22 cmof distilled water to a weighed polystyrene cup.

;easure the steady temperature of the water.

1dd anhydrous aluminium chloride to the polystyrene cup, with stirring.

;easure the highest temperature reached.

Le@weigh the polystyrene cup and contents

Data

;ass of anhydrous aluminium chloride 7 5.22 g

;ass of solution 7 25 g

:nitial temperature 7 3./ 4CHighest temperature reached 7 5./ 4C

Apecific heat capacity of the solution 7 5.2 * g+

4C+

(i) Calculate the heat change in this e#periment.

(2)

(ii) 1ssuming that 22 cmof water is a large e#cess, calculate the enthalpy change, in

%* mol+

, when one mole of aluminium chloride reacts. :nclude a sign and unit in your

answer.

(3)

(Total 5 marks)

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41. (a) (i) Write the equation which represents the change occurring when the standard

enthalpy of atomisation of bromine is measured.

...........................................................................................................................(2)

(ii) $efine latt'%e ener!$.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

(3)

(b) 1 Eorn@Haber cycle for the formation of magnesium chloride is shown below.

; g - < ( g ) < - C l ( g ) < - e +

; g - < ( g ) < C l - ( g ) < - e+ -


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The theoretically calculated 9alue for the lattice energy of magnesium chloride is

+--> %* mol+

.

6#plain, in terms of the bonding in magnesium chloride, why the e#perimentally

determined 9alue of +-/-> %* mol

+

is significantly different from the theoretical 9alue.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................(2)

(c) The table shows 9alues for the lattice energies of the metal chlorides of some Iroup -

metals.

Iroup - metalchloride

;gCl- CaCl- ArCl- EaCl-

attice energy

%* mol+ +-/-> +--3 +-- +-20

6#plain why these lattice energies become less e#othermic from ;gCl-to EaCl-.

(3)

(Total 10 marks)

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42. 1n e#periment was carried out to find the enthalpy change for the reaction of Oinc powder with

copper(::) sulphate solution.

Vn(s) < CuA!5(aq) VnA!5(aq) < Cu(s)

/2cmof copper(::) sulphate solution, of concentration .2 mol dm

+, was put into a polystyrene

cup and the temperature of the solution measured. 1fter one minute, /.2 g of Oinc powder was

added, the mi#ture stirred with a thermometer and the temperature measured e9ery 2 s.

(a) (i) What is meant by a spectator ion?

...........................................................................................................................

...........................................................................................................................

(1)

(ii) Ii9e the formula of the spectator ion in this reaction.

...........................................................................................................................(1)

(iii) Write the equation for this reaction, omitting the spectator ion.

(1)

(b) How would you measure the /2 cmof copper(::) sulphate solution?

.....................................................................................................................................

.....................................................................................................................................(1)

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(c) Ii9e TW! reasons why it is better to use a polystyrene cup, rather than a metal container,

to obtain more accurate results.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................(2)

(d) Calculate the number of moles of each of the reactants and hence deduce which reactant

is completely used up.


;oles of Oinc powder

;oles of copper(::) sulphate

Leactant used up .................................................................(3)

(e) The following results were obtained.

Time s 2 >2 2 -2 /2 02 -2

Temperature 4C -- -- >2 >/ > > /

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(i) !n the graph paper below, plot the results of this e#periment.

3 2

> 2

/ 2

5 2

2

- 2

, 2

2

T e m p e r a t u r e X C

2 5 2 0 2 , - 2 , > 2 - 2 2 - 5 2

T i m e s(2)

(ii) 6#plain the shape of your graph

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(2)

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(iii) The ma#imum recorded temperature in this e#periment was >/4C. &se your graph

to estimate a more accurate ma#imum temperature.

...........................................................................................................................(1)

(f) (i) Calculate the energy change in this e#periment using your answer to (e)(iii) and the

relationship

energy change 7 mass of 8 specific heat capacity 8 temperature r'se

solution of solution

* g * 4C+

g+

4C

"ou may assume that

.2 cmof solution has a mass of .2 g

The specific heat capacity of the solution is 5.- * 4C+

g+

(1)

(ii) &se your answers to (d) and (f)(i) to calculate ZH for this reaction. :nclude a sign

and units in your answer.

(3)

(Total 18 marks)

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43. This question is about the chemistry of propane, CH0.

Propane is sold for use as a fuel for camping sto9es. !n complete combustion it forms carbon

dio#ide and water.

(a) The enthalpy change of combustion of propane, 'Hc, can be measured by burning a

%nown mass of propane below a container of water and measuring the temperature rise of

the water.

The heat capacity of the apparatus (the energy required to raise the temperature of the

apparatus by 4C) is found by calibrating it with a fuel with %nown enthalpy change of

combustion.

The results of an e#periment are shown below.

;ass of propane burned 2./22 g

Temperature of water at start -.2 4C

Minal temperature of water .2 4C

Heat capacity of apparatus ./ %* 4C+

(i) Calculate the number of %iloDoules of energy transferred when the 2./22 g sample

of propane burns in this e#periment.(1)

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(ii) &se your answer to (i) to calculate 'Hcfor propane in %* mol+

. Ii9e your answer

to three s'!n'&'%ant &'!"res.


(2)

(iii) TheBook of data gi9es the 9alue of 'Hcfor propane as +---2 %* mol

+

.

Calibrating the apparatus means that the answer you calculated in (ii) allows for

errors due to heat loss.

Auggest the other main source of error which ma%es the e#perimental result

different from the data boo% 9alue.

...........................................................................................................................

...........................................................................................................................(1)

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(b) 1 9alue of 'Hc for propane can be calculated using mean bond energies and the Hess

cycle below.

(i) Complete the Hess cycle, and use the mean bond energies to calculate 'H.

Hence calculate 'Hc.

;ean bond energies

%* mol+

C7! 02/

H+! 5>5

H c

C H 0 ( g ) < . . . . . . . . . . ! - ( g ) C ! - ( g ) < 5 H - ! ( g )

< > 5 2 % * m o l+ ,

H , 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

C ( g ) < 0 H ( g ) < . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

'Hc 7 ................................................................................................................(3)

(ii) Ii9e !B6 reason why the 9alue you calculated in (b)(i) also differs from the 9alue

for the heat of combustion of propane in theBook of data.

...........................................................................................................................

...........................................................................................................................

(1)

(c) When propane reacts with chlorine in the presence of ultra9iolet light one of the products

is -@chloropropane.

(i) Bame the mechanism and type of this reaction.

;echanism .......................................................................................................

Type ..................................................................................................................

(2)

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(ii) :n this reaction a small quantity of an al%ane, C>H5, is produced.

6#plain how this occurs. :nclude an equation in your answer.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(2)

(d) -@Chloropropane and -@iodopropane are both colourless liquids at room temperature.

They can be distinguished by their reactions with aqueous sil9er nitrate.

(i) What would you see when the reaction is carried out with each halogenoal%ane?

-@chloropropane ...............................................................................................

-@iodopropane ..................................................................................................(2)

(ii) Write an ionic equation showing how sil9er ions react in the mi#ture made from -@

iodopropane and aqueous sil9er nitrate. :nclude state symbols in your answer.

(2)

(iii) Eoth -@chloropropane and -@iodopropane form the same organic product in the

reaction with aqueous sil9er nitrate.

Bame, or gi9e the structural formula of, this organic product.

...........................................................................................................................(1)

(Total 17 marks)

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44. This question is about some of the chemicals used in car engines and their reactions.

(a) Compound , shown below, is one component of petrol.

H \ C \ \ C \ \ C \ \ C \ \ C \ H

H C H H H H

H C H H HC H

(i) Bame .

...........................................................................................................................(1)

(ii) Ii9e the em#'r'%al formula of .

...........................................................................................................................(1)

(iii) can be made by crac%ing decane, C2H--.

1ssuming only one other product forms in a crac%ing reaction, deduce the

mole%"lar formula of this other product.

(1)

(i9) What is the sign of the enthalpy change for the reaction in which decane is

crac%ed? Ii9e a reason for your answer.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(1)

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(9) :f the air supply in a car engine is poor, there is not enough air for carbon dio#ide

to be produced.

&se this information to suggest !B6 possible equation for the combustion of in

this engine. &se the molecular formula of in your equation.

(2)

(b) When air enters a car engine, as well as the fuel burning, nitrogen and o#ygen can react to

form nitrogen(::) o#ide.

B-(g) < !-(g) -B!(g) 'H 7 < 02 %* mol+

(i) What, if any, is the effect on the percentage of nitrogen(::) o#ide in an equilibrium

mi#ture of these three gases if the pressure and temperature are increased?

6#plain your answers.

:ncrease in pressure

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

:ncrease in temperature

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(2)

(ii) :n a car e#haust pipe, nitrogen(::) o#ide passes o9er a catalytic con9erter.

The following reaction occurs.

-B!(g) < -C!(g) = B-(g) < -C!-(g) 'H 7 +35> %* mol+

6#plain why this reaction speeds up when the car engine has been running for a

few minutes.

...........................................................................................................................

...........................................................................................................................

(1)

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(iii) 1 te#tboo% says ^The catalytic con9erter con9erts the gases coming out of the

engine into less harmful ones_.

Atate, with a reason, which of the four gases in the equation in (ii) you consider to

be least harmful.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................(1)

(i9) The diagram below shows the reaction profile for the change which occurs in the

catalytic con9erter.

6 n e r g y

- B ! ( g ) < - C ! ( g )

B ( g ) < - C ! ( g )- -

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

!n the diagram, show the acti9ation energy,E1.

1dd a line showing the reaction profile if no catalyst is present.(2)

(Total 12 marks)

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45. (a) $efine the term standard enthal#$ o& &ormat'on.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................(3)

(b) The dissociation of phosphorus pentachloride is a re9ersible reaction.

PCl/(g) PCl(g) < Cl-(g)

(i) &se the 9alues of enthalpy of formation gi9en to calculate ZH for the forward

reaction.

ZHf

%* mol+

PCl/(g) +

PCl(g) + 2>

(1)

(ii) 6#plain, with reasons, the effect that raising the temperature would ha9e on the

composition of the equilibrium mi#ture.

...........................................................................................................................

...........................................................................................................................

.............................................................................................................