topic 13 thermochemistry

7/30/2019 Topic 13 Thermochemistry

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TOPIC

1

13: THERMOCHEMISTRY

Which of the following reactions absorbs heat from the surroundings?

Antara tindak balas berikut, yang manakah menyerap haba daripadapersekitaran?

A Adding zinc to nitric acidMenambahkan zink pada asid nitrik

B Dissolving ammonium nitrate in waterMelarutkan ammonium nitrat dalam air

C Dissolving copper(II) sulphate in waterMelarutkan kuprum(II) sulfat dalam air

D Adding sodium hydroxide solution to sulfuric acid

Menambahkan larutan natrium hidroksida pada asid sulfurik

2 Which of the following chemicals when dissolved in water will reduce thetemperature?

Antara bahan berikut, yang manakah menurunkan suhu apabila dilarutkandalam air?

A Sodium oxideNatrium oksida

B Ammonium nitrateAmmonium nitrat

C Copper(II) sulphateKuprum(II) sulfat

D Potassium hydroxide

Kalium hidroksida


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TOPIC 13: THERMOCHEMISTRY

3 Figure 11 shows the energy level diagram that represents the reaction between A

and B.

Rajah 11 menunjukkan gambar rajah aras tenaga mewakili tindak balas antara A

dan B.

What is the heat of the reaction between A and B?

Apakah haba tindak balas antara A dan B?

A

B

C

D

T2T2T1

T3 - T1T3T2

4 The heat of neutralisation between hydrochloric acid and potassium hydroxide is

higher than the heat of neutralisation between ethanoic acid and potassiumhydroxide because

Haba peneutralan antara asid hidroklorik dan kalium hidroksida adalah lebih

tinggi daripada haba peneutralan antara asid etanoik dan kalium hidroksida

kerana

A

B

C

D

hydrochloric acid is a mineral acid whereas ethanoic acid is an organic acid

asid hidroklorik adalah asid mineral sementara asid etanoik adalah asid

organik

the reaction between ethanoic acid and potassium hydroxide is incomplete

tindak balas antara asid etanoik dan kalium hidroksida adalah tidak

lengkaphydrochloric acid and ethanoic acid have different pH values

asid hidroklorik dan asid etanoik mempunyai nilai pH yang berlainan

energy is needed to ionise the ethanoic acid

tenaga diperlukan untuk mengion asid etanoik

Figure 11


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Trial kedah 2009

5 Figure 14 shows the energy level diagram for a reaction between zinc and

copper(II) sulphate solution.

Rajah 14 menunjukkan gambar rajah aras tenaga bagi tindak balas antara zink

dan larutan kuprum(II) sulfat.

Calculate the temperature change when excess zinc is added to 100 cm3 of0.1 mol dm

3copper(II) sulphate solution .

Kira perubahan suhu apabila zink berlebihan ditambah kepada 100 cm3

larutan

kuprum(II) sulfat 0.1mol dm3

.

[Specific heat capacity of water = 4.2 J g-1

oC

-1]

A

B

C

D

2oC

4oC

6oC

8oC

6 The following is a thermochemical equation.

Berikut ialah suatu persamaan termokimia.

HCl + NaOH NaCl + H2O H = -57 kJ/mol

Calculate the quantity of heat energy released when 200 cm3

2.0 mol dm-3

hydrochloric acid is added to 300 cm3

2.0 mol dm-3

sodium hydroxide solution.

Hitung kuantiti haba yang dibebaskan apabila 200 cm3

2.0 mol dm-3

asid

hidroklorik ditambah kepada 300 cm3

2.0 mol dm-3

larutan natrium hidroksida.

A

BC

D

5.70 kJ

11.4 kJ17.1 kJ

22.8 kJ

7 Which of the following reactions releases heat to the surroundings?Antara tindak balas berikut, yang manakah membebaskan haba ke persekitaran?

A Dissolving potassium nitrate in waterMelarutkan kalium nitrat dalam air

B Disssolving ammonium sulphate in waterMelarutkan ammonium sulfat dalam air

C Adding calcium carbonate to nitric acidMenambahkan kalsium karbonat kepada asid nitrik

D Adding potassium hydrogen carbonate to hydrochloric acidMenambah kalium hidrogen karbonat kepada asid hidroklorik

Figure 14


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8 The following equation shows the reaction between potassium hydroxide solution andnitric acid.Persamaan berikut menunjukkan tindak balas antara larutan kalium hidroksida dan asid nitrik

KOH(aq) + HNO3(aq) KNO3(aq) + H2O(l) H = - 57kJ mol-1

Which of the following statements is true?Antara pernyataan berikut, yang manakah benar?

A The reaction is endothermicTindak balas ini adalah endotermik

B The heat is absorbed from the surroundingsHaba diserap dari persekitaran

C The temperature of the solution mixtures risesSuhu larutan campuran meningkat

D 57 kJ of heat energy is absorbed to form 1 mole of water57 J tenaga haba diserap untuk membentuk 1 mol air

9 Diagram 14 shows the energy level diagram for the reaction between zinc andcopper(II) sulphate solution .

Rajah 14 menunjukkan gambar rajah aras tenaga bagi tindak balas antara zink dan larutankuprum(II) sulfat.

Diagram 14Rajah 14

What is the change in temperature when 50 cm3 of 0.1 mol dm-3 copper(II) sulphatesolution is reacted with excess zinc?[Specific heat capacity of solution = 4.2 Jg-1C-1]

Berapakah perubahan suhu jika 50 cm3 larutan kuprum(II) sulfat 0.1 mol dm-3ditindakbalaskandengan zink berlebihan?[Muatan haba tentu larutan = 4.2 Jg

-1C

-1]

A 2.1CB 2.6CC 5.2CD 8.2C

Energy

Zn(s) + CuSO4 (aq)

ZnSO4 (aq) + Cu(s)

H= - 217 kJmol-1

Tenaga


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10 When 25 cm3 of 1.0 mol dm-3 hydrochloric acid is mixed with 25 cm3 of 1.0 mol dm-3potassium hydroxide solution the temperature increases 14C.What is the heat change for this reaction?[Specific heat capacity of solution = 4.2J g C-1]

Apabila 25 cm3

asid hidroklorik 1.0 mol dm-3

dicampurkan dengan 25 cm3

larutan kalium

hidroksida 1.0 mol dm-3suhu meningkat sebanyak 14C.Berapakah perubahan haba bagi tindak balas ini?[Muatan haba tentu larutan = 4.2J g C

-1]

A 1470 JB 2352 JC 2940 JD 3280J

11 The following equation shows the reaction between Ag+

and Cl-ions.

Berikut adalah persamaan bagi tindakbalas antara ion Ag+

dan ion Cl-.

Ag

+

+ Cl

-

AgCl H = - 65 kJmol

-1

Which of the following is true about the above equation ?

Antara berikut yang manakah benar tentang persamaan diatas ?

A Endothermic reaction occurs

Tindakbalaas endotermik berlaku

B Heat is released to the surroundings

Haba dibebaskan ke persekitaran

C The temperature of the product decreases

Suhu hasil tindakbalas berkurang .

D 65 kJ of heat absorbed when 1 mole of silver chloride is formed .

65 kJ haba diserap apabila 1 mol argentum klorida terbentuk .

12 Table 6 shows the heat of combustion of three alcohols .

Jadual 6 menunjukkan haba pembakaran bagi tiga alkohol.

Alcohol

Alkohol

Heat of combustion / kJmol-

Haba pembakaran /kJmol-1

CH3OH -710

C2H5OH -1370

C4H9OH -2670

Which of the following factors increases the heat of cobustion of alcohols ?

Antara faktor berikut , yang manakah menambahkan haba pembakaran alkohol ?

A Size of molecules decreases

Saiz molekul berkurang

B Number of carbon atoms per molecule increases

Bilangan atom karbon per molekul bertambah

C Number of oxygen atoms per molecule increases

Bilangan atom oksigen per molekul bertambah

D Number of hydrogen atoms per molecule decreasesBilangan atom hidrogen per molekul berkurang


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13 Diagram 15 shows energy level diagrams for the reaction between hydrochloric acid

and potassium hydroxide .

Rajah 15 menunjukkan gambarajah aras tenaga untuk tindakbalas antara asid

hidroklorik dan kalium hidroksida .

Diagram 15

Rajah 15

Calculate the amount of heat released when 50 cm3

of 2 mol dm-3

hydrochloric acid

reacts with 50 cm3

of 2 mol dm-3

potassium hydroxide solution.

Hitungkan jumlah haba yang dibebaskan apabila 50 cm3

asid hidroklorik 2 mol dm-3

bertindak balas dengan 50 cm3

larutan kalium hidroksida2 mol dm-3

A 5.40 kJB 10.8 kJ

C 27.0 kJ

D 54.0 kJ

14 The following equation shows the combustion of heptane, C7H16 in excess oxygen.

Persamaan berikut menunjukkan pembakaran heptana, C7H16 dalam oksigen

berlebihan.

C7H16 + 11O2 7CO2 + 8H2O H = - 5512 kJ mol-1

In an experiment the combustion of heptane in excess oxygen releases 1378 kJ energy.

What is the mass of heptane used?

Dalam satu eksperimen pembakaran heptana dalam oksigen berlebihan membebaskan

1378 kJ tenaga.

Berapakah jisim heptana yang digunakan?

[Relative atomic mass : H = 1; C = 12]

[Jisim atom relatif: H = 1 ; C = 12 ]

A 25.0 g

B 36.0 g

C 77.0 g

D 88.0g

H+

+ OH-

H 2 O

- 54 kJ mol-1

Energy

Tenaga


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15 The following is the energy level diagram for the neutralization reaction betweenhydrochloric acid and sodium hydroxide solution.

Which of the following statements is true?

A The reaction is endothermicB The heat energy absorbed is 57 kJC The temperature of the product increasesD The products contain more energy than the reactants

16Table 3 shows the heat of neutralization between acids and alkalis for experiment I and

experiment II.

Experiment Acid Alkali Heat of neutralization/kJmol-1

I Ethanoic acid Sodium hydroxide -55.0II Nitric acid Sodium hydroxide -57.0

TABLE 3

Why is the heat of neutralization of experiment I is lower than experiment II?

A Ethanoic acid is a weak acidB Ethanoic acid ionizes partially in the waterC Ethanoic acid released more energy to the surroundingsD Ethanoic acid absorb parts of the energy released to ionized in water

17 The thermochemical equation represents the precipitation of lead(II) sulphate :Persamaan termokimia mewakili tindak balas bagi pemendakan plumbum(II) sulfat:

Pb2+

(aq) + SO42-

(aq) PbSO4(s) H = 42 kJ mol-1

Which energy level diagram is correct ?

Gambar rajah aras tenaga manakah yang betul ?

Energy

HCl + NaOH

NaCl + H2O

H = - 57 kJ mol-1


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18 Diagram 8 shows the set up of apparatus to determine the heat of combustion ofpropanol.

DIAGRAM 8

Thermometer

Water

Spirit lamp

Ethanol

Glass beaker

XXXXXXXX

A

PbSO4(s)

Energy

Tenaga H = 42 kJ mol-1

Pb2+(aq) + SO42-(aq)

B

PbSO4(s)

Energy

Tenaga H = + 42 kJ mol-1

Pb2+

(aq) + SO42-

(aq)

C Pb2+

(aq) + SO42-

(aq)

Energy

Tenaga H = 42 kJ mol-1

PbSO4(s)

D

Pb2+

(aq) + SO42-

(aq)

Energy

Tenaga H = + 42 kJ mol-1

PbSO4(s)


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The value of the heat of combustion obtained is less than the theoretical value. Which ofthe following can improve the accuracy of the value obtained?Nilai haba pembakaran yang diperolehi adalah lebih rendah daripada nilai teori. Antaraberikut, yang manakah dapat meningktkan ketepatan nilai yang diperolehi?

I Remove the wire gauzeII Touch the thermometer to the base of the beakerIII A copper can is used to replaced the glass beakerIV The flame from the spirit lamp must touch the bottom of the beaker

A I, II and IV onlyB I, III and IV onlyC II, III and IV onlyD I, II, III and IV

19 The following is the chemical equation for a reaction.

Pb(NO3)2 + Na2SO4 PbSO4 + 2NaNO3

2.52 kJ of heat energy is released when 0.05 mol of lead(II) sulphate precipitate isformed. Calculate the heat of precipitation of lead(II) sulphate.

A 0.02 kJmol-1

B 0.13 kJmol-1C 5.04 kJmol-1D 50.40 kJmol-1

20 The following is the energy level diagram.

What is the mass of calcium carbonate decomposed if 8.8 kJ of heat energy isabsorbed?[Relative atomic mass: C=12, O=16, Ca=40]

A 2.5 g C 7.5 gB 5.0 g D 10.0 g

Energy

CaCO3(s)

CaO(s) + CO2(g)

H = + 176 kJ mol-1


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21 The diagram shows the energy level diagram for the decomposition of calcium carbonate.

Rajah menunjukkan gambar rajah aras tenaga bagi penguraian kalsium karbonat.

Based on the energy level diagram, which of the following is true?

Berdasarkan gambar rajah aras tenaga, manakah betul?

A The reaction is exothermicTindak balas adalah eksotermik

B The heat energy released is y kJTenaga haba yang dibebaskan ialah y kJ

C CaO(s) and CO2(g) contain more energy than the CaCO3(s)Kandungan tenaga CaO(s) and CO2(g) lebih daripada kandungan tenagaCaCO3(s)

D Heat absorbed during the breaking of bond in CaCO3 is less than the heat releasedduring the formation of bond.

Haba yang diserap semasa pemecahan ikatan dalam CaCO3adalah rendahdaripada haba yang dibebaskan semasa pembentukan ikatan

CaO(s) + CO2(g)

CaCO3 (s)

Energy

Tenaga

H = + y kJmol-1


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22 The diagram shows the set-up of the apparatus to determine the heat of precipitation ofsilver chloride.

Rajah menunjukkan gambar rajah susunan radas untuk menentukan habapemendakan bagi argentum klorida.

What is the heat of precipitation of silver chloride?Berapakah haba pemendakan bagi argentum klorida?

[Specific heat capacity of solution = 4.2 Jg-1oC-1, density of solution = 1 gcm-3]

[Muatan haba tentu larutan = 4.2 Jg-1oC-1, ketumpatan larutan = 1 gcm-3]

A

B

C

D

18.9 kJmol-

37.8 kJmol-1

18900 kJmol-1

37800 kJmol-1

Thermometer

Termometer

28.0oC 28.0

oC

Polystyrene cup

Cawan

+

25 cm3 of 1.0 moldm-3 ofsilver nitrate solution

25 cm3 larutanargentum nitrat 1.0

50 cm3 of 1.0 moldm-3 ofsodium chloride solution

50 cm3 larutan natriumklorida 1.0 moldm-3

Thermometer

TermometerStir

Kaca31.0

oC

Mixture of the solution

Campuran larutan

White precipitate

Mendakan putih


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23 The following is the thermochemical equation for a reaction.

Berikut adalah persamaan termokimia bagi satu tindak balas

Calculate the heat change when 50 cm3 of 1.0 moldm-3 copper(II) sulphate solution reactswith excess zinc.

Hitung perubahan haba apabila 50 cm3 larutan kuprum(II) sulfat 1.0 moldm-3bertindak balas dengan zink yang berlebihan.

A

B

C

D

10.5 kJ

105 kJ

420 kJ

4200 kJ

24 The thermochemical equation for the precipitation of lead(II) chloride , PbCl2 is given

below.

Persamaan termokimia bagi pemendakan plumbum(II) klorida , PbCl2 diberikan

seperti di bawah.

Pb2+

(aq) + 2 Cl

(aq) PbCl2(s) H = 50 kJ mol-1

Pb2+(ak) + Cl(ak) PbCl2(p) H = 50 kJ mol-1

Which statement is true ?

Pernyataan manakah yang benar?

A The reaction is endothermic.

Tindak balas adalah endotermik.

B The temperature of the reaction mixture increases.

Suhu campuran bahan tindak balas meningkat.

C The energy content of the PbCl2 is higher than that of Pb+

and Cl

ions.

Kandungan tenaga PbCl2 adalah lebih tinggi dari jumlah tenaga ion

Pb2+dan ion Cl

D Energy is absorbed when 1 mole of PbCl2 is formed.

Tenaga diserap apabila 1 mol PbCl2 terbentuk

Zn + CuSO4 ZnSO4 + Cu H = -210 kJmol-1


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25 The thermochemical equation for displacement of copper by zinc is given below.

Persamaan termokimia bagi penyesaran kuprum oleh zink diberikan seperti

dibawah.

Zn(s) + CuSO4 (aq) ZnSO4 (aq) + Cu(s) H = 210 kJ mol-1

Zn(p) + CuSO4 (ak) ZnSO4 (ak) + Cu(p) H = 210 kJ mol-1

What is the mass of copper, Cu when 84 kJ of heat is released?

[Relative atomic mass: Cu = 64]

Berapakah jisim kuprum, Cu yang terbentuk apabila 84 kJ haba dibebaskan?

[Jisim atom relatif: Cu = 64]

A 0.4 g

B 3.3 g

C 25.6 g

D 160.0 g

26 The heat of neutralisation between a strong acid and a strong alkali

is57.6 kJmol-1

.Which reactions release less than 57.6 kJmol-1

?

Haba peneutralan antara asid kuat dan alkali kuat

adalah 57.6 kJ mol-1

Tindak balas manakah yang membebaskan

tenaga haba kurang dari 57.6 kJmol-1

?

I 1 mol of ammonia solution with 1 mol of hydrochloric acid

1 mol larutan ammonia dengan 1 mol asid hidroklorik

II 1 mol of potassium hydroxide solution with 1 mol of nitric acid.

1 mol larutan kalium hidroksida dengan 1 mol asid nitrik

III 1 mol of potassium hydroxide solution with 1 mol of ethanoic acid.

1 mol larutan kalium hidroksida dengan 1 mol asid etanoik

IV 1 mol of sodium hydroxide solution and 0.5 mol of sulphuric acid.

1 mol larutan natrium hidroksida dengan 0.5 mol asid sulfurik

A I and III

I dan IIIB I and IV

I dan IV

C II and III

II dan III

D II and IV

II dan IV


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27 The particulars below are obtained from an experiment to determine the heat of

combustion of butanol .

Volume of water = 250 cm3

Mass of butanol burnt = 0.37 gIncrease in water temperature = 12.8

oC

What is the heat of combustion of butanol?

[Specific heat capacity of water = 4.2 J g-1

oC

-1, Relative molecular mass of butanol =

74 ]

Butiran berikut diperolehi dari satu eksperimen bagi menentukan haba pembakaran

butanol.

Isipadu air = 250 cm3

Jisim butanol = 0.37 gKenaikan suhu air = 12.8 C

Berapakah haba pembakaran butanol?

[Muatan haba tentu air = 4.2 J g-1

oC

-1,Jisim molekul relatif butanol = 74]

A - 1630 kJ mol-

B - 2688 kJ mol-

C - 4973 kJ mol-

D - 6070 kJ mol-

28 Diagram 13 shows the energy profile diagram of the following chemical reaction.

Rajah 13 menunjukkan gambar rajah profil tenaga bagi tindak balas kimia berikut.

L + M R + S

Energy 70kJTenaga

200 kJ

L + M

Which of the following statements is true?Antara pernyataan-pernyataan berikut, yang manakah benar?

A

B

The heat of reaction is 70 kJHaba tindak balas bagi tindak balas ialah 70 kJ.

The activation energy is 200 kJ.Tenaga pengaktifan bagi tindak balas adalah 200 kJ.

Diagram 13Rajah 13

R + S


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C

D

R and S are more stabil than L and M.R dan S adalah lebih stabil daripada L dan M.

Heat is released when L reacts with M to produce R and S.Haba terbebas apabila

Lbertindak balas dengan

Muntuk menghasilkan R dan S.

PAPER 2

SECTION A

1. Diagram 6 shows the energy level diagram for the combustion of methanol.Rajah 6 menunjukkan gambar rajah aras tenaga bagi pembakaran metanol.

CO2 + 2H2O

(a) State one information that can be obtained from the energy level diagram inDiagram 6.

Nyatakan satu maklumat yang boleh diperolehi daripada gambar rajah aras tenaga dalamRajah 6.

..

[1 mark]

EnergyTenaga

CH3OH +2

3O2

H = -728 kJ mol-1

Diagram 6Rajah 6


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(b) Draw a labelled diagram of the set up of apparatus to determine the heat ofcombustion of methanol.Lukis gambar rajah susunan radas yang berlabel bagi menentukan haba pembakaranmetanol.

[2 marks]

(b) Heat energy released from the complete combustion of 1.6 g methanol is usedto heat 200 cm3 of water.Haba yang terbebas daripada pembakaran lengkap 1.6 g metanol digunakan untukmemanaskan 200 cm

3air.

(i) Calculate the heat energy released in the reaction.Hitung tenaga haba yang dibebaskan dalam tindak balas ini.

[ Molar mass of methanol, CH3OH = 32 gmol-1 ]

[ Jisim molar metanol CH3OH = 32 gmol-1

]

[2 marks]


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(ii) Calculate the temperature change in the reaction.Hitung perubahan suhu dalam tindak balas ini.

[ Specific heat capacity of water: 4.2 J g -1oC-1 ][ Muatan haba tentu air:4.2 J g-1oC-1 ]

[2 marks]

(c) The value of the heat of combustion of methanol obtained from the experimentalways less than the theoretical value.

Suggest one precaution step that should be taken in order to get a moreaccurate result.Nilai haba pembakaran metanol yang diperolehi daripada eksperimen biasanya lebihrendah daripada nilai teori.Cadangkan satu langkah berjaga-jaga yang perlu diambil untuk memperolehikeputusan yang lebih tepat.

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

..........................................................................................................................................[1 mark]

(d) Table 6 shows the molecular formula and heat of combustion of ethanol andpropanol.

Jadual 6 menunjukkan formula molekul dan haba pembakaran etanol dan propanol.

Name of alcoholNama alkohol

Molecular formulaFormula molekul

Heat of combustion/ kJmol-1Haba pembakaran/ kJmol

-1

EthanolEtanol

C2H5OH -1376

PropanolPropanol

C3H7OH - 2015

Table 6Jadual 6


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Based on the information in Table 6, explain why there is a difference in thevalue of heat of combustion between ethanol and propanol.Berdasarkan maklumat dalam Jadual 6, terangkan mengapa terdapat perbezaan nilaiHaba pembakaran antara etanol dan propanol.

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

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

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

[3 marks]

2. The equation for combustion of propanol in excess oxygen is given below.Persamaan tindakbalas pembakaran propanol dalam oksigen berlebihan diberikan seperti

berikut.

C3H7OH + 9 O2 3CO2 + 4H2O H= -2015 kJ mol-1

2

(a) State one information that can be obtained from the given equation.Nyatakan satu maklumat yang boleh diperolehi daripada persamaan yang diberikan.

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

[1 mark]

(b) Heat given out from the complete combustion of 1.2 g propanol is used to heat200 cm3 of water.Haba yang terbebas daripada pembakaran lengkap 1.2 g propanol digunakan untukmemanaskan 200 cm

3air.

Calculate:Hitung:


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(i) The heat energy given out in the reaction.Tenaga haba yang dibebaskan dalam tindak balas ini.

[Molar mass of propanol, C3H7OH = 60 gmol-1]

[Jisim molar bagi propanol, C3H7OH = 60 gmol-1]

[2 marks]

(ii) The temperature change in the reaction.Perubahan suhu dalam tindak balas ini.

[ Spesific heat capacity of water = 4.2 Jg-1 o

C-1

; Density of water = 1 gcm-3

][ Muatan haba tentu bagi air = 4.2 Jg-1 oC-1 ; Ketumpatan air = 1 gcm-3 ]

[2 marks]


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(c) Draw the energy level diagram for this reaction.Lukis gambarajah aras tenaga bagi tindak balas ini.

[3 marks]

(d)The value of the heat of combustion of propanol obtained from the experiment is lessthan the theoretical value. Suggest one precaution step that should be taken in orderto get a more accurate result.

Nilai haba pembakaran propanol yang diperolehi daripada eksperimen ini lebih rendahdaripada nilai teori. Cadangkan satu langkah berjaga-jaga yang perlu diambil untukmemperolehi keputusan yang lebih tepat.

..........................................................................................................................................[1 mark]

(e) Table 6 shows the molecular formula and the heat of combustion for methanoland ethanol.

Jadual 6 menunjukkan formula molekul dan haba pembakaran bagi methanol dan etanol.


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AlcoholAlkohol


Heat of combustion/kJmol-1Haba pembakaran/kJmol

-1

MethanolMethanol

CH3OH -728

EthanolEtanol

C2H5OH -1376

Based on the information in Table 6, explain why there is a difference in the value ofheat of combustion between methanol and ethanol.Berdasarkan maklumat dalam Jadual 6, terangkan mengapa terdapat perbezaan nilai habapembakaran antara metanol dan etanol.

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

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

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

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

[3 marks]

Table 6Jadual 6


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3 The thermochemical equation below represents the combustion reaction of an alcohol in the

air.

Persamaan termokimia dibawah mewakili tindak balas pembakaran suatu alkohol di udara.

C4H9OH + 6O2 4CO2 + 5H2O H = -2679 kJ mol-1

(a) (i) State the name of the alcohol in the above equation.

Nyatakan nama alkohol di dalam persamaan di atas.

[1 mark]

[1markah]

(ii) What is meant by H = -2679 kJ mol-

in the above equation?

Apakah yang dimaksudkan dengan H = -2679 kJ mol-1\ dalam persamaan

di atas?

[1 mark]

[1markah]

(b) 0.37g of the alcohol that is named in (a), used to heat 500 g of water.

0.37g alkohol yang dinamakan di (a), digunakan untuk memanaskan 500 g air.

Calculate,

Hitungkan,

(i) the heat released by the alcohol in the reaction.

[Molar mass of the alcohol = 74 g mol-1

]

haba yang dibebaskan oleh alkohol itu dalam tindak balas

[Jisim molar alkohol = 74 gmol-1

]

[1 mark]

[1markah]

(ii) the temperature change of water expected in the experiment in (b)

[Specific heat capacity of water: 4.2 J g-1

oC

-1]

perubahan suhu air yang dijangkakan dalam eksperimen ini.

[Haba tentu air: 4.2 J g-1oC-1]

[2 marks]

[2markah]


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(c) Draw the energy level diagram for the combustion of the alcohol.

Lukiskan gambar rajah aras tenaga untuk pembakaran alkohol tersebut.

[2 marks]

[2markah]

(d) Table 6 shows the heat of combustion of various alcohols.

Jadual 6 menunjukkan haba pembakaran pelbagai alkohol.

Number of

carbon atoms

Bilangan atom

karbon

Molecular formula

Formula molekul

Name of alcohol

Nama alkohol

Heat of

combustion

Haba pembakara

(kJ mol-1

)

1 CH3OH Methanol -726

2 C2H5OH Ethanol -1376

3 C3H7OH Propanol .

4 C4H9OH -2679

5 C5H11OH Pentanol -3332

Table 6

Jadual 6

(i) Predict the heat of combustion of propanol.

Ramalkan haba pembakaran bagi propanol.

[1 mark]

[1markah]


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(ii) Based on Table 6, explain why as the number of carbon atoms increases so does the

value of heat of combustion.

Berdasarkan Rajah 6, terangkan mengapa apabila bilangan atom karbon

bertambah nilai haba pembakaran juga bertambah.

[2 marks]

[2markah]


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5 g of zinc powder5 g sebuk zink

50 cm3

of 0.2 mol dm-3

copper(II) sulphate solution50cm3 larutan kuprum(II)sulfat0.2 mol dm-3

Plastic cupCawan plastik

6 Diagram 6 shows the apparatus set-up to determine heat of displacement of copper byusing zinc powder.The temperature changes is recorded in the Table 6.Rajah6 menunjukkan susunan radas untuk menentukan haba penyesaran bagi

kuprum dengan menggunakan serbuk zink.Perubahan suhu dicatat dalam Jadual6.

Diagram 6Rajah6

Initial temperature of copper(II) sulphate solution (oC)Suhu awal larutan kuprum(II) sulfat(oC)

30.0

Highest temperature of the mixture (oC)Suhu tertinggi campuran(oC)

38.0

Table 6Rajah6

(a) What is the meaning of heat of displacement?Apakah yang dimaksudkan dengan haba penyesaran?

...

... [1 mark]

(b) State the type of reaction that occurs based on the temperature change.Nyatakan jenis tindak balas yang berlaku berdasarkan perubahan suhu.

... [1 mark]


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(c) Calculate :Kira:

(i) the heat change for the reaction[Specific heat capacity of solution = 4.2 J g-1oC-1; Density of solution = 1 g cm-3]

perubahan haba bagi tindak balas.[Muatan haba tentu larutan= 4.2J g-1oC-1; Ketumpatan larutan = 1 g cm-3]

[1 marks]

(ii) the heat of displacement for the reaction.haba penyesaran bagi tindak balas.

[2 marks]

(d) Draw energy level diagram for the reaction.Lukiskan gambar rajah aras tenaga bagi tindak balas tersebut.

[3 marks]


27/32

(e) Experiment I is repeated by using 100 cm3 of 0.2 mol dm-3 of copper(II) sulphate

solution.EksperimenI diulangi dengan menggunakan100 cm3 larutan kuprum(II)sulfat 0.2 mol dm-3.

(i) Based on Experiment I, predict the heat change for the reaction.Berdasarkan EksperimenI, ramalkan perubahan haba bagi tindakbalas tersebut.

... [1 mark]

(ii) Explain your answer in (e) (i).Terangkan jawapan dalam(e) (i).

...

...

... [2 marks]

4 (a) Chemical reactions involve the breaking of bonds of the reactants and the formationof bonds of the products. By using a suitable example, explain the concept ofendothermic reaction in term of the breaking and the formation of bonds in a reaction.

[3 marks]

(b) 50.0 cm3 of silver nitrate solution 1.0 mol dm-3 is reacted with 50.0 cm3 of sodiumchloride solution 0.5 mol dm-3 . The data obtained is shown in Table 6.

Initial temperature of silver nitrate solution/oC 29.0

Initial temperature of sodium chloride solution/ oC 29.0

Maximum temperature of the mixture/ oC 36.5

(i)Write the chemical equation for the reaction.

[2 marks]

(ii)Calculate the number of moles of the silver ions that react with the chloride ions.

[1 mark]

TABLE 6


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(iii) Calculate the heat change in this reaction.[Specific heat capacity of solution = 4.2 Jg-1oC-1, Density of solution = 1 gcm-3]

[2 marks]

(iv) Calculate the heat of precipitation for this reaction.

[2 marks]

(c) Diagrams 3 shows the energy level of Reactions I and II.

Based on the energy level diagrams above, compare Reaction I and Reaction II.

[3 marks](d) The information shows two equations which represent the reactions between

acid andalkali with their respective heat of neutralization .

Based on the information of H above, compare and contrast Reaction I andReaction II. Include in your answer the ionic equations for both reactions.

[4 marks]

Zn + CuSO4

ZnSO4 + Cu

H = -210 kJ mol-

Energy

CaCO3

CaO + CO2

H = +178 kJ mol-1

Energy

Reaction I Reaction II

Experiment I

HCl(aq) + KOH(aq) NaCl(aq) + H2O(l) H= -57 kJ mol-1

Experiment II

CH3COOH(aq) + NaOH(aq) CH3COONa(aq) + H2O(l) H= -55 kJ mol-1

DIAGRAM 3


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(e) Table 7 shows the molecular formula and heat of combustion for methanol andethanol.

Alkohol Formula molekul Haba Pembakaran/ kJ mol-1

Metanol CH3OH -725

Etanol C2H5OH -1376

Based on the information in Table 7, explain why there is a difference in the valuesof the heat of combustion between methanol and ethanol.

[3 marks]

10 (a) What is meant by the heat of combustion of alcohol ?

Apakah maksud haba pembakaran alkohol ?[2 marks]

(b) Table 10 shows the molecular formula and the heat of combustion for alcohol X and

alcohol Y.

Jadual 10 menunjukkan formula molekul dan haba pembakaran bagi alkohol X dan

alkohol Y.

Table 10

Based on the information in Table 10, compare the heat of combustion between alcohol

X and alcohol Y. Explain why there is a difference in the values of the heat of

combustion between alcohol X and alcohol Y.

Berdasarkan maklumat dalam Jadual 10, bandingkan haba pembakaran antara alkohol

X dan alkohol Y. Terangkan mengapa nilai haba pembakaran bagi alkohol X dan

alkohol Y berbeza.

[3 marks]

(c) Name one example of an alcohol and describe a laboratory experiment to determine

the heat of combustion of that alcohol.

In your description, include a labelled diagram and the calculation involved.

[ Relative atomic mass : C=12, O=16 , H=1]

[ Specific heat capacity of solution = 4.2.J g-1 o

C-1

;Density of solution =1gcm-3

]

Dengan menggunakansatu contoh alkohol yang dinamakan, huraikan satu eksperimen

makmal untuk menentukan haba pembakaran alkohol itu. Dalam penerangan anda,

Alcohol

Alkohol

Molecular Formula

Formula molekul

Heat of Combustion/ kJ mol-1

Haba Pembakaran/ kJ mol-1

X C3H7OH -2100

Y C4 H9OH -2877

TABLE 7


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sertakan gambar rajah berlabel dan langkah pengiraan yang terlibat.

[Jisim atom relatif : C=12, O= 16, H=1]

[ Muatan haba tentu larutan = 4.2 J g-1

oC

-1; Ketumpatan larutan = 1 g cm

-3]

[12 marks]

(d) In an experiment to determine the heat of displacement, excess zinc is added to 100 cm

of 0.5 mol dm-3

silver nitrate solution. Calculate the temperature change if the heat of

displacement is -105 kJ mol-1

[Specific heat capacity of the solution = 4.2Jg-1

oC

-1; Density of solution=1gcm

-3]

Dalam satu eksperimen untuk menentukan haba penyesaran, zink berlebihan

ditambahkan kepada 100 cm3

0.5 mol dm-3

larutan argentum nitrat. Hitungkan

perubahan suhu jika haba penyesaran dalam eksperimen itu ialah -105 kJ mol-1 .

[ Muatan haba tentu larutan =4.2 Jg-1

oC

-1; Ketumpatan larutan = 1gcm

-3]

[ 3 marks]

8 (a) Combustion of alcohols is an exothermic reaction.

(i) Write the equations for the combustion of methanol and ethanol. Using these two

equations, explain why the heat of combustion of methanol and ethanol differs.

Pembakaran alkohol merupakan suatu tindak balas eksotermik.

(i) Tuliskan persamaan untuk pembakaran methanol dan etanol. Dengan menggunakan

kedua-dua persamaan ini, terangkan mengapa haba pembakaran metanol dan etanol

adalah berbeza.

[5 marks]

(ii) Sketch a graph to show the relationship between the heat of combustion of the first

five alcohols against the number of carbon atoms per molecule.

Lakarkan satu graf untuk menunjukkan hubungan antara haba pembakaran lima

alkohol pertama dengan bilangan atom karbon per molekul.

[ 2 marks]

(b) (i) Explain what is meant by the heat of precipitation using the formation of silver

chloride as an example.

Terangkan maksud haba pemendakan dengan menggunakan tindak balas

pembentukan argentum klorida sebagai contoh.

[2 marks]

(ii) Describe an experiment to determine the heat of precipitation of silver chloride.

Include a labelled diagram, the experimental procedure and the calculation in your

description.

Terangkan satu eksperimen untuk menentukan haba pemendakan bagi argentum

klorida . Penerangan anda mesti mengandungi gambarajah berlabel, prosedur

eksperimen dan pengiraan.


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10. Diagram 10 shows the energy diagram for two reactions.Rajah 10 menunjukkan gambarajah aras tenaga bagi dua tindak balas.

Diagram 10Rajah 10

(a) Compare and contrast between the energy level diagrams for reaction Iand reaction II.Banding bezakan di antara gambar rajah aras tenaga bagi tindak balasdan tindak balas II.

[4 marks][4 markah]

(b) Table 10 shows the molecular formula and the heat of combustion forethanol and propanol.Jadual 10 menunjukkan formula molekul dan haba pembakaran bagi

etanol dan propanol.

AlcoholAlkohol


Heat of combustion/kJ mol-

Haba pembakaran/kJ mol-1

EthanolEtanol

C2H5OH -1376

PropanolPropanol

C3H7OH -2026

Table 10Jadual 10

Based on the information in table 10, compare the heat of combustionbetween ethanol and propanol. Explain why there is a difference in thevalues of the heat of combustion between ethanol and propanol.Berdasarkan maklumat dalam jadual 10, bandingkan haba pembakarandi antara etanol dan propanol. Terangkan mengapa terdapat perbezaannilai haba pembakaran bagi etanol dan propanol.

[4 marks][4 markah]

(c) The heat of combustion of ethanol can be determined in the laboratory.Describe how to determine the heat of combustion of ethanol.

Haba pembakaran etanol boleh ditentukan di makmal. Huraikanbagaimana untuk menentukan haba pembakaran etanol.

Energy

Tenaga

Energy

Tenaga

Reactants

Bahan tindak balas

Products

Hasil tindak balas

Reactants

Bahan tindak balas

Products

Hasil tindak balas

Reaction I

Tindak balas I

Reaction II

Tindak balas II


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Your answer should include the following:Jawapan anda perlu mengandungi perkara-perkara berikut:

Diagram of apparatus set-upGambar rajah susunan radas

Procedure of the experimentProsedur eksperimen

Three precautionary steps to get better resultsTigalangkah berjaga-jaga untuk mendapat keputusan lebih baik

[12 marks]

topic 13 thermochemistry

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