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R1.3 Energy from fuels

Practice exam-style IB Chemistry questions for Energy from fuels, aligned with the syllabus and grouped by topic.

Verified by Dennis M.
Verified by Dennis M.
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Question 1
SL • Paper 1A
Easy
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SL • Paper 1A
Easy
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A methane burner supplied with too little oxygen is most likely to produce:

A.

a blue flame and only CO2CO_2 and H2OH_2O

B.

a white solid of magnesium oxide

C.

a colourless flame and oxygen gas

D.

a smoky yellow flame and carbon particles

Question 2
SL • Paper 1A
Easy
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SL • Paper 1A
Easy
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The equation that represents photosynthesis in green plants is:

A.

C6H12O6→2C2H5OH+2CO2C_6H_{12}O_6 \to 2C_2H_5OH + 2CO_2

B.

C2H5OH+3O2→2CO2+3H2OC_2H_5OH + 3O_2 \to 2CO_2 + 3H_2O

C.

6CO2+6H2O→C6H12O6+6O26CO_2 + 6H_2O \to C_6H_{12}O_6 + 6O_2

D.

2H2O→2H2+O22H_2O \to 2H_2 + O_2

Question 3
HL • Paper 1A
Easy
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HL • Paper 1A
Easy
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The feature that distinguishes a fuel cell from a primary voltaic cell is that a fuel cell:

A.

converts electrical energy into chemical energy

B.

has reactants supplied continuously from outside the cell

C.

always produces no chemical waste products

D.

stores a fixed amount of reactants inside the cell

Question 4
SL • Paper 1A
Easy
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SL • Paper 1A
Easy
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In the combustion of magnesium, the oxidizing agent and reducing agent are respectively:

A.

oxygen and magnesium oxide

B.

oxygen and magnesium

C.

magnesium oxide and oxygen

D.

magnesium and oxygen

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Question 5
SL • Paper 1A
Easy
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SL • Paper 1A
Easy
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The sum of the coefficients in the balanced equation for the complete combustion of pentane, C5H12C_5H_{12}, using whole-number coefficients is:

A.

20

B.

13

C.

21

D.

19

Question 6
SL • Paper 1A
Easy
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SL • Paper 1A
Easy
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In the incomplete combustion of ethanol to form carbon monoxide and water, the coefficient of O2O_2 in the balanced equation is:

A.

22

B.

44

C.

33

D.

11

Question 7
SL • Paper 1A
Easy
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SL • Paper 1A
Easy
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The cathode half-equation in an acidic hydrogen fuel cell is:

A.

2H2+O2→2H2O2H_2 + O_2 \to 2H_2O

B.

2H++2e−→H22H^+ + 2e^- \to H_2

C.

O2+4H++4e−→2H2OO_2 + 4H^+ + 4e^- \to 2H_2O

D.

H2→2H++2e−H_2 \to 2H^+ + 2e^-

Question 8
HL • Paper 1A
Easy
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HL • Paper 1A
Easy
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A useful liquid fuel often has a relatively high activation energy for combustion because this means the fuel:

A.

will react spontaneously with oxygen at room temperature

B.

can be stored in air but still burn when deliberately ignited

C.

has a positive enthalpy change of combustion

D.

releases no carbon dioxide during complete combustion

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Question 9
SL • Paper 2
Easy
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SL • Paper 2
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Magnesium ribbon burns in oxygen with an intense white flame to form magnesium oxide.

A

the balanced equation for the combustion of magnesium in oxygen.

[1]
B

Identify the oxidizing agent in this reaction.

[1]
Question 10
SL • Paper 2
Easy
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SL • Paper 2
Easy
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Propan-1-ol, C3H7OHC_3H_7OH, is an alcohol that can be used as a fuel.

A

the balanced equation for the complete combustion of propan-1-ol. symbols are not required.

[2]
Question 11
HL • Paper 1A
Medium
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HL • Paper 1A
Medium
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Larger hydrocarbons have a greater tendency to undergo incomplete combustion because they generally have:

A.

fewer carbon atoms per molecule and lower boiling points

B.

more oxygen atoms in each molecule and higher flammability

C.

stronger London dispersion forces and lower volatility

D.

weaker London dispersion forces and higher volatility

Question 12
HL • Paper 1A
Medium
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HL • Paper 1A
Medium
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Carbon dioxide is described as a greenhouse gas because it:

A.

absorbs some infrared radiation emitted by Earth

B.

reacts with nitrogen to form ozone in the stratosphere

C.

absorbs most visible radiation arriving from the Sun

D.

has a higher concentration than nitrogen in the atmosphere

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Question 13
HL • Paper 1A
Medium
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HL • Paper 1A
Medium
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The anode half-equation for an acidic direct methanol fuel cell is:

A.

CH3OH+H2O→CO2+6H++6e−CH_3OH + H_2O \to CO_2 + 6H^+ + 6e^-

B.

CO2+6H++6e−→CH3OH+H2OCO_2 + 6H^+ + 6e^- \to CH_3OH + H_2O

C.

1.5O2+6H++6e−→3H2O1.5O_2 + 6H^+ + 6e^- \to 3H_2O

D.

CH3OH+1.5O2→CO2+2H2OCH_3OH + 1.5O_2 \to CO_2 + 2H_2O

Question 14
SL • Paper 2
Medium
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SL • Paper 2
Medium
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A camping stove burning butane, C4H10C_4H_{10}, is used in a poorly ventilated space.

A

one visible observation that may indicate incomplete combustion.

[1]
B

Write a balanced equation for the incomplete combustion of butane to form carbon monoxide and water.

[1]
C

why carbon monoxide is a health risk.

[1]
Question 15
SL • Paper 2
Medium
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SL • Paper 2
Medium
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Ethanol can be manufactured from plant material and used as a biofuel.

A

the equation for photosynthesis.

[1]
B

why ethanol from plants may have a lower net carbon footprint than a petroleum fuel.

[2]
Question 16
SL • Paper 1B
Medium
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SL • Paper 1B
Medium
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A student compared several liquid fuels by burning each fuel under a copper calorimeter containing water. The table shows the formula of each fuel, its molar mass, the mass burned and the temperature change of the water.

Fuel

Formula

Molar mass / g mol−1^{-1}

Mass burned / g

Water volume / cm3\text{cm}^{3}

Temperature change / ∘C^\circ\text{C}

methanol

CH3OH\text{CH}_3\text{OH}

32.0

0.600

200

15.8

ethanol

C2H5OH\text{C}_2\text{H}_5\text{OH}

46.1

0.800

200

24.0

propan-1-ol

C3H7OH\text{C}_3\text{H}_7\text{OH}

60.1

1.00

200

32.0

A

the experimental energy released per gram of ethanol using q=mcΔTq=mc\Delta T. Assume the density of water is 1.00 g cm−31.00\ \text{g cm}^{-3} and the specific heat capacity of water is 4.18 J g−1 K−14.18\ \text{J g}^{-1}\ \text{K}^{-1}.

[2]
B

the balanced equation for the complete combustion of ethanol.

[1]
C

one reason why the experimental value is less exothermic than the data book value for ethanol.

[1]

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Question 17
SL • Paper 1B
Medium
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SL • Paper 1B
Medium
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The diagram shows an acidic hydrogen fuel cell connected to an external circuit. Hydrogen and oxygen are supplied continuously to different electrodes.

A

the half-equation at the anode.

[1]
B

the overall cell reaction from the two electrode half-equations.

[2]
C

one difference between a fuel cell and a primary voltaic cell.

[1]
Question 18
HL • Paper 1A
Medium
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HL • Paper 1A
Medium
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The standard enthalpies of combustion of methane and propane are −890 kJ mol−1-890\ \text{kJ mol}^{-1} and −2220 kJ mol−1-2220\ \text{kJ mol}^{-1} respectively. The approximate masses of CO2CO_2 produced when each fuel is burned completely to release 2220 kJ2220\ \text{kJ} are:

A.

methane: 44 g44\ \text{g}; propane: 44 g44\ \text{g}

B.

methane: 220 g220\ \text{g}; propane: 264 g264\ \text{g}

C.

methane: 110 g110\ \text{g}; propane: 132 g132\ \text{g}

D.

methane: 132 g132\ \text{g}; propane: 110 g110\ \text{g}

Question 19
SL • Paper 2
Medium
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SL • Paper 2
Medium
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The table gives data for the complete combustion of two gaseous fuels. Use the data to the mass of CO2CO_2 released per 1.00 MJ1.00\ MJ of energy released.

Fuel

ΔHc∘^\circ / kJ mol−1\text{mol}^{-1}

CO2CO_2 produced / mol per mol fuel

M(CO2)M(CO_2) / g mol−1^{-1}

Methane

-891

1

44.01

Propane

-2220

3

44.01

A

the mass of CO2CO_2 produced per 1.00 MJ1.00\ MJ of energy released by methane, using ΔHcθ=−891 kJ mol−1\Delta H_c^\theta = -891\ kJ\ mol^{-1}.

[2]
B

Propane releases 2220 kJ mol−12220\ kJ\ mol^{-1} and produces three moles of CO2CO_2 per mole of propane. the mass of CO2CO_2 produced per 1.00 MJ1.00\ MJ of energy released by propane, and which fuel releases less CO2CO_2 per unit energy.

[2]
Question 20
SL • Paper 2
Medium
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SL • Paper 2
Medium
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A hydrogen fuel cell operates under acidic conditions with hydrogen and oxygen supplied continuously.

A

the half-equation at the anode.

[1]
B

the half-equation at the cathode.

[1]
C

two differences between a fuel cell and a primary voltaic cell.

[2]

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Question 21
HL • Paper 2
Medium
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HL • Paper 2
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Carbon dioxide is described as a greenhouse gas, whereas nitrogen and oxygen are not significant greenhouse gases.

A

the type of radiation absorbed by greenhouse gases such as CO2CO_2.

[1]
B

, in molecular terms, why CO2CO_2 is a greenhouse gas but N2N_2 and O2O_2 are not significant greenhouse gases.

[2]
Question 22
HL • Paper 2
Medium
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HL • Paper 2
Medium
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Longer-chain hydrocarbon fuels often burn with a smokier flame than short-chain hydrocarbon fuels under similar conditions.

A

which hydrocarbon, methane or octane, has the greater tendency to undergo incomplete combustion.

[1]
B

this tendency in terms of intermolecular forces and mixing with oxygen.

[2]
Question 23
HL • Paper 2
Medium
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HL • Paper 2
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A direct methanol fuel cell operates under acidic conditions. Methanol is oxidized at one electrode and oxygen is reduced at the other.

A

the anode half-equation for the acidic methanol fuel cell.

[1]
B

the cathode half-equation using six electrons.

[1]
C

the overall cell reaction and one environmental disadvantage of using methanol in this fuel cell.

[2]
Question 24
HL • Paper 2
Medium
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HL • Paper 2
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Petrol is highly exothermic when it burns, but it does not usually ignite spontaneously in air at room temperature.

A

Define activation energy.

[1]
B

why a relatively high activation energy is a useful property of a fuel.

[2]

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Question 25
SL • Paper 1B
Medium
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SL • Paper 1B
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A gas burner was adjusted to change the air supply while burning propane. The exhaust gases and deposits on a cool ceramic tile were monitored.

Air supply / %

CO2CO_2 in exhaust / %

COCO in exhaust / %

Soot on tile / mg

100

12.0

0.0

0.0

80

10.4

0.2

0.1

60

7.8

0.9

0.6

40

4.5

2.5

1.7

20

1.2

5.0

3.8

A

the effect of decreasing the air supply on the products of combustion.

[2]
B

the balanced equation for incomplete combustion of propane forming carbon monoxide and water only.

[1]
C

why operating the burner with very low air supply increases health risk.

[1]
Question 26
SL • Paper 1B
Medium
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SL • Paper 1B
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The table gives data for three fossil fuels used to produce heat. Carbon dioxide emissions per unit energy can be estimated from the mass of carbon dioxide formed and the specific energy of the fuel.

Fuel

CO2CO_2 formed from 1 kg fuel / kg

Specific energy / MJ kg−1^{-1}

Natural gas

2.75

55.5

Propane

3.00

46.4

Butane

3.03

45.7

A

Identify the fuel in the table that releases the least CO2CO_2 per unit energy when burned completely.

[1]
B

the mass of CO2CO_2 released per MJMJ of energy when propane is burned completely.

[2]
C

why the fuel with the lowest direct CO2CO_2 emission per unit energy may still not be the best choice in all situations.

[1]
Question 27
SL • Paper 1B
Medium
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SL • Paper 1B
Medium
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Life-cycle data were collected for ethanol produced from two different crops and for petrol. Negative values represent carbon dioxide removed from the atmosphere during plant growth.

Fuel

Plant growth / g CO2CO_2e MJ−1MJ^{-1}

Production / g CO2CO_2e MJ−1MJ^{-1}

Processing / g CO2CO_2e MJ−1MJ^{-1}

Transport / g CO2CO_2e MJ−1MJ^{-1}

Combustion / g CO2CO_2e MJ−1MJ^{-1}

Sugarcane ethanol

-75

15

6

4

68

Wheat ethanol

-60

20

8

5

68

Petrol

0

7

10

4

73

A

the reactants and products of photosynthesis.

[1]
B

Using the data, the net life-cycle emission for sugarcane ethanol.

[2]
C

one disadvantage of using the crop-based biofuel shown by the data.

[1]
Question 28
HL • Paper 1B
Medium
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HL • Paper 1B
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The graph compares the intensity of radiation from the Sun and Earth with the infrared absorption of atmospheric carbon dioxide.

A

Identify the radiation region in which CO2CO_2 absorbs most strongly in relation to Earth’s emitted radiation.

[1]
B

how this absorption contributes to the greenhouse effect.

[2]
C

why increasing the concentration of CO2CO_2 changes the energy balance even though CO2CO_2 is a minor component of air.

[1]

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Question 29
HL • Paper 1B
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HL • Paper 1B
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Several straight-chain alkanes were burned in identical burners with the same air flow. The table gives physical properties and measurements of incomplete-combustion products.

Alkane

Carbon atoms

Boiling point / ∘C^\circ\text{C}

Soot collected / mg

butane

4

-1

0.2

pentane

5

36

0.8

hexane

6

69

1.9

heptane

7

98

3.5

octane

8

126

5.8

nonane

9

151

8.7

A

the relationship between carbon chain length and soot formation shown by the data.

[1]
B

why larger hydrocarbons have a greater tendency to undergo incomplete combustion under these conditions.

[2]
C

one change to the burner that would reduce carbon monoxide and soot formation.

[1]
Question 30
HL • Paper 2
Medium
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HL • Paper 2
Medium
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A power station is choosing between coal and natural gas. The data the energy released and the carbon dioxide emitted when equal masses of fuel are burned.

Fuel

Energy released / MJ kg−1^{-1} fuel

CO2_2 emitted / kg CO2_2 kg−1^{-1} fuel

Coal

24

2.40

Natural gas

50

2.75

A

Using the data, the mass of CO2CO_2 emitted per MJMJ of energy released for coal, using 24 MJ kg−124\ MJ\ kg^{-1} and 2.40 kg2.40\ kg CO2CO_2 per kgkg fuel.

[1]
B

Natural gas releases 50 MJ kg−150\ MJ\ kg^{-1} and produces 2.75 kg2.75\ kg CO2CO_2 per kgkg fuel. the mass of CO2CO_2 emitted per MJMJ of energy released for natural gas.

[1]
C

one advantage and one limitation of choosing natural gas rather than coal.

[2]
Question 31
HL • Paper 2
Medium
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HL • Paper 2
Medium
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A company claims that ethanol made from maize is carbon neutral because the maize plants absorb carbon dioxide as they grow.

A

the process by which maize plants convert atmospheric carbon dioxide into organic compounds.

[1]
B

why the combustion of ethanol does not by itself prove that the fuel is carbon neutral.

[1]
C

two life-cycle factors that could make the net greenhouse gas emissions of the biofuel higher than claimed.

[2]
Question 32
SL • Paper 1B
Hard
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SL • Paper 1B
Hard
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A direct methanol fuel cell was compared with a compressed hydrogen fuel cell for a small portable power unit. The table gives fuel properties.

Fuel

State at 25∘C25^\circ\text{C}

Specific energy / MJ kg−1^{-1}

Energy density / MJ dm−3^{-3}

Methanol (CH3OHCH_3OH)

liquid

23

18

Compressed hydrogen (H2H_2)

compressed gas

120

4.8

A

the change in oxidation of carbon when methanol, CH3OHCH_3OH, is converted to CO2CO_2 in the fuel cell.

[1]
B

The anode reaction is CH3OH(aq)+H2O(l)→CO2(g)+6H+(aq)+6e−CH_3OH(aq)+H_2O(l)\to CO_2(g)+6H^+(aq)+6e^-. the cathode half-equation and the overall reaction.

[2]
C

Using the data, one advantage and one disadvantage of methanol compared with compressed hydrogen for the portable power unit.

[2]

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Question 33
HL • Paper 1B
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HL • Paper 1B
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The table shows infrared absorption information for common atmospheric gases. Molecular diagrams show whether selected vibrations change the molecular dipole.

Gas

Abundance / ppmv

Molecular type / polarity

Example vibration

Dipole change?

Absorbs terrestrial IR?

N2N_2

780000

Homonuclear diatomic, non-polar

Stretching

No

No

O2O_2

209000

Homonuclear diatomic, non-polar

Stretching

No

No

CO2CO_2

420

Linear, non-polar overall

Bending / asymmetric stretching

Yes

Yes

H2OH_2O

variable

Bent, polar

Bending / stretching

Yes

Yes

CH4CH_4

1.9

Tetrahedral, non-polar overall

Asymmetric stretching / bending

Yes

Yes

A

Using the data, identify two gases that are significant infrared absorbers in the terrestrial infrared region.

[1]
B

why N2N_2 and O2O_2 are not significant greenhouse gases, using the molecular information.

[2]
C

Carbon dioxide is linear and non-polar overall. why it can still absorb infrared radiation.

[1]
Question 34
HL • Paper 1B
Hard
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HL • Paper 1B
Hard
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The graph shows global fossil-fuel carbon emissions, atmospheric CO2CO_2 concentration and global mean temperature anomaly over the same period.

Year

Fossil-fuel CC emissions / Gt C yr−1^{-1}

Atmospheric CO2CO_2 / ppm

Global mean temperature anomaly / ∘C^\circ\text{C}

1960

2.5

316

-0.04

1970

3.7

325

-0.01

1980

5.0

339

0.14

1990

6.0

354

0.28

2000

6.8

369

0.22

2010

8.5

390

0.63

2015

9.1

401

0.79

2020

9.6

414

1.02

A

two trends shown by the data.

[2]
B

how combustion of fossil fuels can lead to an increase in atmospheric CO2CO_2 concentration.

[1]
C

whether the graph alone proves that increasing CO2CO_2 is the only cause of the observed temperature change.

[2]
Question 35
SL • Paper 2
Hard
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SL • Paper 2
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Magnesium ribbon burns with a bright white flame. Butan-1-ol, C4H9OHC_4H_9OH, can also be used as a fuel when ignited in air.

A

Combustion reactions can be described using balanced equations and redox terminology.

I.

the balanced equation, including symbols, for the combustion of magnesium in oxygen.

[1]
II.

Identify the oxidizing agent and reducing agent in the reaction in (a)(i).

[1]
III.

why a fuel with a reasonably high activation energy can be useful.

[1]
B

the balanced equation for the complete combustion of butan-1-ol, C4H9OH(l)C_4H_9OH(l), forming liquid water.

[2]
C

why the complete combustion of butan-1-ol is exothermic in terms of bond breaking and bond forming.

[2]
Question 36
SL • Paper 2
Hard
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SL • Paper 2
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A camping stove burning propane, C3H8C_3H_8, is used in a poorly ventilated space. A yellow smoky flame is observed.

A

The combustion of propane may be complete or incomplete depending on the oxygen supply.

I.

the balanced equation for the complete combustion of propane forming liquid water.

[1]
II.

a balanced equation for incomplete combustion of propane forming carbon monoxide and liquid water.

[1]
III.

a balanced equation for incomplete combustion of propane forming carbon and liquid water.

[1]
B

two observations expected when propane burns in a limited supply of oxygen.

[2]
C

why the use of the stove in a poorly ventilated space is hazardous.

[2]

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Question 37
SL • Paper 2
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SL • Paper 2
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A hydrogen fuel cell can power an electric vehicle by reacting hydrogen with oxygen to produce water.

A

In an acidic hydrogen fuel cell, oxidation occurs at the anode and reduction occurs at the cathode.

I.

the anode half-equation.

[1]
II.

the cathode half-equation.

[1]
III.

the overall equation for the reaction in the hydrogen fuel cell.

[1]
IV.

the direction of electron flow in the external circuit.

[1]
B

and a hydrogen fuel cell with a primary voltaic cell.

[2]
C

why a hydrogen fuel cell may be described as clean at the point of use but not necessarily carbon-free over its life cycle.

[1]
Question 38
HL • Paper 1B
Hard
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HL • Paper 1B
Hard
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Hydrogen for fuel-cell vehicles can be produced by different routes. The table compares two hydrogen-production routes with direct use of petrol in an engine.

Vehicle / fuel option

Upstream / g CO2CO_2 equivalent km−1\text{km}^{-1}

Use-phase / g CO2CO_2 equivalent km−1\text{km}^{-1}

Methane reforming H2 + fuel cell

92

0

Renewable electrolysis H2 + fuel cell

0

0

Petrol + engine

20

180

A

the total CO2CO_2 equivalent emission per kilometre for hydrogen made by methane reforming and used in a fuel cell, using the upstream and use-phase data.

[1]
B

why the statement “a hydrogen fuel cell vehicle produces no carbon dioxide” is incomplete.

[2]
C

which option in the table gives the best overall environmental outcome. Use two pieces of evidence from the data.

[2]
Question 39
HL • Paper 1B
Hard
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HL • Paper 1B
Hard
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A proposed bioethanol project would replace some petrol use. The figure summarizes annual carbon flows and selected impacts for the project.

Category

Item

Annual value / kt CO2e yr−1\text{kt CO}_2\text{e yr}^{-1}

Selected impact / note

Carbon flow

CO2CO_2 absorbed by crop growth

-90

Carbon flow

Cultivation emissions

+18

Carbon flow

Processing emissions

+22

Carbon flow

Transport emissions

+40

Carbon flow

Combustion emissions

+35

Baseline

Continued petrol use emissions

70

Impact

Feedstock land use

Some arable land would no longer grow food crops

Impact

Water demand

High irrigation demand in dry months

Impact

Distribution of benefits

Most profits go to the company; local farmers bear costs

A

the net annual change in greenhouse gas emissions for the project relative to continued petrol use.

[2]
B

why bioethanol cannot automatically be described as carbon neutral.

[2]
C

Using the figure, one social or ethical concern that should be considered before approving the project.

[1]
Question 40
SL • Paper 2
Hard
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SL • Paper 2
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A school is comparing methane, propane and octane as possible fuels for a portable heater. The table gives selected data for complete combustion under standard conditions.

Fuel

Formula

ΔHc∘^\circ / kJ mol−1\text{mol}^{-1}

Specific energy / kJ g−1^{-1}

Boiling point / ∘C^\circ\text{C}

Methane

CH4CH_4

-890

55.6

-161.5

Propane

C3H8C_3H_8

-2220

50.5

-42.1

Octane

C8H18C_8H_{18}

-5470

48.0

125.6

A

The combustion data can be used to fuels quantitatively.

I.

Using the balanced equation for methane combustion, the mass of CO2CO_2 produced when 1.00 mol1.00\ \text{mol} of methane burns completely.

[1]
II.

the mass of CO2CO_2 produced per 1000 kJ1000\ \text{kJ} of energy released by complete combustion of methane, using ΔHcθ=−890 kJ mol−1\Delta H_c^\theta = -890\ \text{kJ mol}^{-1}.

[2]
III.

why specific energy, rather than molar enthalpy of combustion alone, is useful when comparing fuels for transport.

[1]
B

why octane has a greater tendency than methane to undergo incomplete combustion in an engine.

[2]
C

whether methane is the best fuel of the three for the heater, using both chemical and practical considerations.

[2]

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Question 41
SL • Paper 2
Hard
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SL • Paper 2
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Ethanol for fuel can be produced from sugar cane. The sugar cane fixes carbon dioxide during photosynthesis and the glucose produced can be fermented to ethanol.

A

The production of ethanol from biomass involves photosynthesis and fermentation.

I.

Write the balanced equation for photosynthesis.

[1]
II.

Write the balanced equation for the fermentation of glucose to ethanol and carbon dioxide.

[1]
III.

the equation for complete combustion of ethanol, C2H5OH(l)C_2H_5OH(l), forming liquid water.

[1]
B

why ethanol made from sugar cane may have a lower net carbon footprint than petrol, but should not automatically be described as carbon neutral.

[3]
C

one environmental advantage and one social or ethical disadvantage of replacing petrol with ethanol from food crops.

[2]
Question 42
SL • Paper 2
Hard
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SL • Paper 2
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Methanol can be used directly in an acidic methanol fuel cell. Methanol is a liquid at room temperature, but it is toxic and the fuel cell produces carbon dioxide.

A

The electrode reactions in an acidic direct methanol fuel cell are redox half-equations.

I.

the anode half-equation for methanol oxidation in acidic solution.

[2]
II.

the cathode half-equation that combines with the anode half-equation in (a)(i).

[1]
III.

the overall equation for the direct methanol fuel cell.

[1]
B

one advantage and two disadvantages of methanol as a fuel for a vehicle fuel cell compared with hydrogen.

[3]
C

why fuel cells can be more efficient than engines that first burn a fuel to produce heat.

[1]
Question 43
HL • Paper 2
Hard
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HL • Paper 2
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Carbon dioxide and methane are greenhouse gases formed or released in processes associated with fossil fuels. Nitrogen and oxygen are the major gases in air.

A

Greenhouse gases interact with infrared radiation emitted by Earth.

I.

the type of radiation absorbed by greenhouse gases after Earth has been warmed by sunlight.

[1]
II.

, at the molecular level, why carbon dioxide is described as a greenhouse gas.

[2]
B

the significance of carbon dioxide and methane as greenhouse gases.

[2]
C

why replacing coal-fired power stations with natural gas can reduce, but not eliminate, climate impact.

[2]
Question 44
HL • Paper 2
Hard
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HL • Paper 2
Hard
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The table compares three hydrocarbons found in petroleum fractions. Their combustion behaviour in an engine depends on both structure and oxygen mixing.

Hydrocarbon

Formula

Carbon atoms

Boiling point / ∘C^\circ\text{C}

hexane

C6H14C_6H_{14}

6

69

decane

C10H22C_{10}H_{22}

10

174

hexadecane

C16H34C_{16}H_{34}

16

287

A

The complete combustion of hydrocarbons can be represented by balanced equations.

I.

the balanced equation for complete combustion of hexane, C6H14(l)C_6H_{14}(l), forming liquid water.

[1]
II.

the amount, in mol, of CO2CO_2 formed by complete combustion of 0.250 mol0.250\ \text{mol} of hexane.

[1]
III.

the mass of CO2CO_2 formed in (a)(ii).

[1]
B

Analyse why the tendency to form soot increases from hexane to hexadecane under the same flame conditions.

[3]
C

one benefit and one limitation of using shorter-chain hydrocarbons as engine fuels.

[2]

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Question 45
HL • Paper 2
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HL • Paper 2
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A fuel supplier compares methane and ethanol by calculating carbon dioxide released for the same useful energy output. Assume complete combustion and that 50.0%50.0\% of the heat released is converted to useful energy for both fuels.

Fuel

Formula

ΔH∘^\circc / kJ mol−1\text{mol}^{-1}

CO2 formed / mol per mol fuel

M(CO2) / g mol−1\text{mol}^{-1}

Methane

CH4

-890

1

44.0

Ethanol

C2H5OH

-1367

2

44.0

A

A device requires 500 kJ500\ \text{kJ} of useful energy.

I.

the heat energy that must be released by combustion to provide 500 kJ500\ \text{kJ} of useful energy at 50.0%50.0\% efficiency.

[1]
II.

Using ΔHcθ(CH4)=−890 kJ mol−1\Delta H_c^\theta(CH_4) = -890\ \text{kJ mol}^{-1}, the amount of methane needed.

[1]
III.

the mass of CO2CO_2 formed from the methane in (a)(ii).

[1]
IV.

Using ΔHcθ(C2H5OH)=−1367 kJ mol−1\Delta H_c^\theta(C_2H_5OH) = -1367\ \text{kJ mol}^{-1}, the mass of CO2CO_2 formed when ethanol provides the same heat release as in (a)(i).

[1]
B

Analyse why methane releases less carbon dioxide than ethanol for the same heat release in this comparison, even though ethanol is a biofuel when produced from biomass.

[2]
C

how increased atmospheric carbon dioxide contributes to the greenhouse effect.

[2]
Question 46
HL • Paper 2
Hard
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HL • Paper 2
Hard
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Hydrogen can be made by electrolysis of water or from fossil fuels. It may then be used in a fuel cell.

A

Hydrogen production and use involve separate redox processes.

I.

Write the overall equation for electrolysis of water to produce hydrogen and oxygen.

[1]
II.

Write the overall equation for a hydrogen fuel cell.

[1]
III.

why the equations in (a)(i) and (a)(ii) do not by themselves prove that the energy cycle is carbon-free.

[2]
B

the operation of a fuel cell with direct combustion of hydrogen in oxygen.

[2]
C

whether hydrogen fuel-cell vehicles should be described as zero-emission vehicles.

[2]
Question 47
HL • Paper 2
Hard
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HL • Paper 2
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A government is considering whether to replace an old coal-fired power station with a natural-gas power station while also investing in pollution control.

Feature

Coal

Natural gas

Renewables

Fuel type

carbon-rich solid; SS impurities

mostly CH4CH_4; very low SS

no fuel burn

H:C ratio

low

high

N/A

Direct CO2CO_2 / g kWh−1kWh^{-1}

900

400

0

SO2SO_2/particles

high

very low

none in operation

Methane leakage

some from mining

possible in supply chain

none in operation

Supply & cost

dispatchable; retrofits costly

dispatchable; moderate capital

variable; high upfront, low running

A

Combustion of sulfur impurities contributes to air pollution.

I.

Write the equation for combustion of sulfur to sulfur dioxide.

[1]
II.

Identify the oxidizing agent in the reaction in (a)(i).

[1]
III.

one environmental consequence of sulfur dioxide emissions.

[1]
B

why natural gas generally releases less carbon dioxide per unit energy than coal.

[2]
C

the environmental, economic and ethical implications of replacing coal with natural gas rather than moving directly to renewable energy.

[3]
Question 48
HL • Paper 2
Hard
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HL • Paper 2
Hard
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An island community is considering three energy carriers for emergency generators: compressed hydrogen for fuel cells, liquid methanol for fuel cells, and diesel for combustion engines.

Energy carrier

Storage / handling

Specific energy / MJ kg−1^{-1}

Energy density / MJ dm−3^{-3}

Point-of-use emissions

Hydrogen

Compressed gas; high-pressure cylinder

120

5.6

Water only

Methanol

Liquid; tank; toxic

20

16

CO2CO_2 and water

Diesel

Liquid; tank; established network

45

36

CO2CO_2, NOxNO_x, SOxSO_x, particulates

A

Energy carriers can be compared using specific energy and energy density.

I.

Define specific energy.

[1]
II.

Define energy density.

[1]
III.

why hydrogen can have high specific energy but still be difficult to store for vehicles or generators.

[1]
B

the overall equation for a methanol fuel cell and use it to identify one point-of-use environmental disadvantage relative to a hydrogen fuel cell.

[2]
C

which energy carrier is most suitable for the island community. Consider reliability, storage and environmental impact.

[3]

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R1.2 Energy cycles in reactions

R1.4 Entropy and spontaneity