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Level 3 Chemistry, 201891390 Demonstrate understanding of thermochemical

principles and the properties of particles and substances

2.00 p.m. Thursday 15 November 2018 Credits: Five

Achievement Achievement with Merit Achievement with ExcellenceDemonstrate understanding of thermochemical principles and the properties of particles and substances.

Demonstrate in-depth understanding of thermochemical principles and the properties of particles and substances.

Demonstrate comprehensive understanding of thermochemical principles and the properties of particles and substances.

Check that the National Student Number (NSN) on your admission slip is the same as the number at the top of this page.

You should attempt ALL the questions in this booklet.

A periodic table and relevant formulae are provided in the Resource Booklet L3–CHEMR.

If you need more room for any answer, use the extra space provided at the back of this booklet and clearly number the question.

Check that this booklet has pages 2 – 11 in the correct order and that none of these pages is blank.

YOU MUST HAND THIS BOOKLET TO THE SUPERVISOR AT THE END OF THE EXAMINATION.

QUESTION ONE

(a) Complete the following table.

Symbol Electron configuration (use s, p, d notation)

V

Cu+

Br–

(b) Explainthefactorsinfluencingthetrendsinfirstionisationenergyandatomicradiusacrossthesecondperiodoftheperiodictable.

Inyouranswer,youshould:

• describethetrendsinbothfirstionisationenergyandatomicradiusacrossthesecondperiod

• explainthefactorsinfluencingthetrendsinfirstionistionenergyandatomicradiusacrossthesecondperiod

• relatethetrendinfirstionisationenergytothetrendinatomicradius.

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(c) (i) Complete the table below.

AsF5 BrF5

Lewis diagram

Name of shape

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(ii) TheLewisdiagramandshapeforXeF4 are given below.

SF

F

F

F

F

FF Xe F

seesaw square planar

ElaborateontheshapeandpolarityofXeF4.

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QUESTION TWO

Thestandardenthalpyofvaporisation,∆vapH°,ofmethanol,propan-1-ol,andpropanal,aregiveninthe table below.

(a) (i) Listalltheforcesofattractionbetweenthemoleculesintheirliquidstate.

Molecule ∆vapH° / kJ mol–1

M / g mol–1 Attractive forces

Methanol

O

H

CH3 OH

CH3CH2CH2 OH

CH3CH2C

38 32

Propan-1-ol

O

H

CH3 OH

CH3CH2CH2 OH

CH3CH2C

47 60

PropanalO

H

CH3 OH

CH3CH2CH2 OH

CH3CH2C30 58

(ii) Compareandcontrasttheenthalpyofvaporisationofmethanol,propan-1-ol,andpropanal.

Youranswershouldincludeanexplanationoftherelativestrengthoftheattractiveforces between the molecules.

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(b) (i) Theequationforthecombustionofpropan-1-olis:

C3H7OH(l) + 4.5O2(g) → 3CO2(g) + 4H2O(l)

Calculatethestandardenthalpyofcombustion,∆cH°,ofpropan-1-ol,giventhefollowingdata:

∆f H°(C3H7OH(l)) = –255 kJ mol–1

∆f H°(CO2(g)) = –394 kJ mol–1

∆f H°(H2O(l)) = –286 kJ mol–1

(ii) Explain how ∆cH°(propan-1-ol)woulddifferifwaterwasproducedasagasratherthanaliquid.

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(c) The equation for the formation of Al2Cl6(s)is:

2Al(s) + 3Cl2(g) → Al2Cl6(s)

Calculatetheenthalpychange,∆rH°,forthisreactionusingthefollowingdata:

2Al(s) + 6HCl(aq) → Al2Cl6(aq) + 3H2(g) ∆rH°=–1003kJmol–1

H2(g) + Cl2(g) → 2HCl(g) ∆rH°= –184kJmol–1

HCl(g) → HCl(aq) ∆rH° = –72.4 kJ mol–1

Al2Cl6(s) → Al2Cl6(aq) ∆rH° = –643 kJ mol–1

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QUESTION THREE

(a) (i) Writeanequationtorepresenttheenthalpyoffusion(melting),∆fusH°,ofwater.

(ii) Whyistheenthalpyofvaporisationofwaterlargerthanitsenthalpyoffusion?

(b) When10.6gofammoniumchloride,NH4Cl,isdissolvedin65.0mLofwater,thetemperatureof the water changes from 20.9°Cto11.5°C.

Themassofthefinalsolutionis75.6g

Assumespecificheatcapacityofaqueousammoniumchloride=4.18Jg–1 °C–1

M(NH4Cl) = 53.5 g mol–1

Calculatetheenthalpychange,∆rH°,fordissolvingammoniumchlorideinwater.

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(c) Thedissolvingofammoniumchlorideinwaterisanendothermicprocess,butammoniumchloridereadilydissolvesinwater.

NH4Cl(s) → NH4+(aq) + Cl–(aq)

Justify,intermsoftheentropychangesofthesystemandthesurroundings,whyammoniumchloridereadilydissolvesinwater.

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QUESTION NUMBER

Extra space if required.Write the question number(s) if applicable.

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QUESTION NUMBER

Extra space if required.Write the question number(s) if applicable.

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