R1.3 Energy from fuels
Practice exam-style IB Chemistry questions for Energy from fuels, aligned with the syllabus and grouped by topic.
Question 1
What are the products of the complete combustion of propane in excess oxygen?
A.
Carbon and hydrogen
B.
Methane and oxygen
C.
Carbon dioxide and water
D.
Carbon monoxide and water
Question 2
What is a fossil fuel?
A.
A renewable fuel formed by photosynthesis each year
B.
A non-renewable carbon-based fuel formed over geological time
C.
A fuel that produces water as its only combustion product
D.
A fuel made from recently grown crops only
Question 3
What are the reactants in photosynthesis?
A.
Carbon dioxide and water
B.
Methane and oxygen
C.
Ethanol and carbon dioxide
D.
Glucose and oxygen
Question 4
Magnesium burns in oxygen to form magnesium oxide. What is the reducing agent in this reaction?
A.
Oxygen
B.
Magnesium
C.
Magnesium oxide
D.
Oxide ions
Question 5
A Bunsen burner flame becomes yellow and deposits black soot on a cool surface. What is the most likely cause?
A.
The fuel has a very low activation energy.
B.
The fuel contains no carbon atoms.
C.
The oxygen supply is limited.
D.
Oxygen is present in excess.
Question 6
What is meant by the specific energy of a fuel?
A.
Energy released per mole of fuel
B.
Energy released per unit mass of fuel
C.
Energy needed to ignite one mole of fuel
D.
Energy released per unit volume of fuel
Question 7
In an acidic hydrogen fuel cell, at which electrode is hydrogen oxidized?
A.
Cathode
B.
Anode
C.
External circuit
D.
Salt bridge
Question 8
Butane, C₄H₁₀, undergoes complete combustion.
Write a balanced equation for the complete combustion of butane.
[1]
State why combustion reactions are described as exothermic.
[1]
Question 9
Explain why a fuel should have a sufficiently high activation energy for safe storage but still be able to burn when ignited. [2]
Question 10
Bioethanol can be produced from glucose.
Write the equation for fermentation of glucose to ethanol and carbon dioxide.
[1]
State why bioethanol is described as renewable only if biomass is regrown sustainably.
[1]
Question 11
Methane burns in a limited supply of oxygen.
State one visible observation expected for incomplete combustion.
[1]
State why carbon monoxide is difficult to detect without a sensor.
[1]
Question 12
What is a valid advantage of using bioethanol instead of petrol as a fuel?
A.
It contains no covalent bonds.
B.
Its carbon can be fixed from atmospheric carbon dioxide over a short timescale.
C.
It never releases carbon dioxide when burned.
D.
It is always more energy dense than petrol.
Question 13
Why is carbon dioxide described as a greenhouse gas?
A.
It reacts rapidly with nitrogen in the atmosphere.
B.
It absorbs some outgoing infrared radiation from Earth.
C.
It absorbs most incoming visible radiation from the Sun.
D.
It reflects all radiation back to the surface.
Question 14
How many electrons are released when one molecule of methanol is oxidized at the anode of an acidic direct methanol fuel cell?
A.
2
B.
8
C.
6
D.
4
Question 15
Hydrogen has a high specific energy but is difficult to store for vehicles. What is the main reason?
A.
Hydrogen has low energy released per unit volume unless compressed or liquefied.
B.
Hydrogen is a solid at room temperature.
C.
Hydrogen produces carbon dioxide in the fuel cell exhaust.
D.
Hydrogen cannot be oxidized electrochemically.
Question 16
A claim states that a biofuel is carbon neutral because plants absorb carbon dioxide. What additional evidence is most important for evaluating the claim?
A.
The exact melting point of carbon dioxide
B.
The number of oxygen atoms in one molecule of ethanol
C.
The full life-cycle emissions from cultivation, processing and transport
D.
The colour of the flame during combustion
Question 17
Ethanol, C₂H₅OH, burns in a limited supply of oxygen.
Write a balanced equation for incomplete combustion of ethanol producing carbon monoxide.
[1]
State one health risk associated with carbon monoxide.
[1]
Question 18
Compare coal and natural gas as fossil fuels.
State one similarity.
[1]
State two advantages of natural gas compared with coal.
[1]
State one disadvantage of natural gas.
[1]
Question 19
A hydrogen fuel cell operates in acidic conditions.
Write the half-equation for oxidation of hydrogen at the anode.
[1]
Write the half-equation for reduction of oxygen at the cathode.
[1]
Question 20
Distinguish between specific energy and energy density for a fuel. [2]
Question 21
The table shows data for three fuels.
| Fuel | Molar mass / g mol⁻¹ | ΔHc / kJ mol⁻¹ | CO₂ / mol mol⁻¹ |
|---|---|---|---|
| Methane | 16.0 | −890 | 1 |
| Ethanol | 46.0 | −1367 | 2 |
| Propane | 44.1 | −2220 | 3 |
Identify the fuel with the highest specific energy.
[1]
Calculate the specific energy of ethanol in kJ g⁻¹ using the data in the table.
[1]
The complete combustion of methane produces one mole of CO₂ per mole of methane. Calculate the mass of CO₂ produced per gram of methane.
[1]
Question 22
A gas burner was operated with different air-hole openings. The graph shows the measured carbon monoxide concentration in the exhaust.
Describe the trend shown in the graph.
[1]
Suggest why carbon monoxide concentration changes as the air-hole opening increases.
[1]
State one safety precaution when using a gas burner indoors.
[1]
Question 23
The diagram shows a hydrogen fuel cell operating in acidic conditions.
Identify the electrode at which oxidation occurs.
[1]
Write the overall reaction for the cell.
[1]
State the direction of electron flow in the external circuit.
[1]
State one reason why the fuel cell may not be carbon neutral over its full life cycle.
[1]
Question 24
Larger hydrocarbons tend to undergo incomplete combustion more readily than smaller hydrocarbons. What is the best explanation?
A.
They contain no carbon–hydrogen bonds to be oxidized.
B.
They have smaller molar masses and therefore vaporize more slowly.
C.
They have stronger London dispersion forces and mix less readily with oxygen vapour.
D.
They require nitrogen rather than oxygen for combustion.
Question 25
In the combustion of magnesium, what is the correct reduction half-equation for oxygen?
A.
Mg → Mg²⁺ + 2e⁻
B.
O₂ + 4e⁻ → 2O²⁻
C.
O₂ → 2O²⁻ + 4e⁻
D.
2O²⁻ → O₂ + 4e⁻
Question 26
Complete combustion of 1.00 mol of butane, C₄H₁₀, produces what amount of carbon dioxide?
A.
2.00 mol
B.
4.00 mol
C.
1.00 mol
D.
6.50 mol
Question 27
What is an important difference between a fuel cell and a primary voltaic cell?
A.
A fuel cell stores all reactants permanently inside the cell.
B.
Only primary cells convert chemical energy into electrical energy.
C.
Only fuel cells contain oxidation and reduction reactions.
D.
A fuel cell receives reactants continuously from outside the cell.
Question 28
Methane has a molar mass of 16.0 g mol⁻¹ and a standard enthalpy of combustion of −890 kJ mol⁻¹.
Calculate the specific energy of methane in kJ g⁻¹.
[1]
Calculate the mass of carbon dioxide formed when 16.0 g of methane undergoes complete combustion.
[1]
Question 29
Explain, in terms of molecular structure and radiation, why carbon dioxide contributes to the greenhouse effect. [3]
Question 30
Kerosene contains longer-chain hydrocarbons than methane.
Explain why longer-chain hydrocarbons may burn less completely.
[1]
State one product, other than water, that indicates incomplete combustion.
[1]
Question 31
A company claims that its biodiesel is “zero-carbon” because it is made from plants.
State the process by which plants fix carbon dioxide into organic compounds.
[1]
Give two reasons why the claim may be misleading.
[1]
Suggest one condition under which the biofuel could have a lower net carbon footprint than diesel.
[1]
Question 32
Compare hydrogen and methanol as fuels for fuel cells.
State one advantage of hydrogen at the point of use.
[1]
State one storage advantage of methanol.
[1]
State one disadvantage of methanol in a fuel cell.
[1]
Question 33
The table summarizes life-cycle information for two liquid fuels used in cars.
| Fuel | Tailpipe CO₂ / g km⁻¹ | Cult./extract. / g CO₂e km⁻¹ | Processing / g CO₂e km⁻¹ | Transport / g CO₂e km⁻¹ | Land-use note |
|---|---|---|---|---|---|
| Petrol | 168 | 18 | 24 | 6 | Crude oil from existing fields |
| Bioethanol blend (E85) | 118 | 32 | 44 | 9 | Crop source varies; land-use change not included |
Identify which fuel has the lower tailpipe CO₂ emission per kilometre.
[1]
State one stage, other than vehicle use, that contributes to the life-cycle emissions of bioethanol.
[1]
Using the data, evaluate whether bioethanol is necessarily carbon neutral.
[1]
Question 34
The graph shows the amount of oxygen needed for complete combustion of members of a homologous series of alkanes, CₙH₂ₙ₊₂.
State the relationship between n and the moles of oxygen required per mole of alkane.
[1]
Deduce the balanced equation for complete combustion of pentane, C₅H₁₂.
[1]
Explain why the graph is linear.
[1]
Question 35
In an acidic direct methanol fuel cell, methanol is oxidized at the anode.
Write the balanced anode half-equation.
[1]
Combine it with the cathode half-equation, 1.5O₂ + 6H⁺ + 6e⁻ → 3H₂O, to give the overall cell reaction.
[1]
Question 36
Complete combustion of propane is represented by:
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
Calculate the mass of CO₂ formed when 22.0 g of propane is burned completely.
[1]
State one reason why the actual amount of CO₂ released per kilometre by a vehicle also depends on engine efficiency.
[1]
Question 37
Discuss two implications, other than the chemical products formed, of continuing large-scale fossil fuel combustion. Include two different categories such as environmental, economic, ethical or social. [4]
Question 38
The graph shows infrared absorption spectra for carbon dioxide and nitrogen over part of the infrared region emitted by Earth.
Identify which gas is the stronger absorber in the region shown.
[1]
Explain why absorption in this region is relevant to the greenhouse effect.
[1]
Suggest why nitrogen is not a significant greenhouse gas, using the data.
[1]
Question 39
The table compares four fuels for transport use.
| Fuel | Specific energy / MJ kg⁻¹ | Energy density / MJ dm⁻³ | State or storage | CO₂ at use / g MJ⁻¹ |
|---|---|---|---|---|
| Hydrogen | 120 | 5.6 | Gas, 700 bar | 0 |
| Methane | 50 | 9.0 | Gas, 250 bar | 55 |
| Methanol | 20 | 16 | Liquid, 1 atm | 69 |
| Petrol | 46 | 34 | Liquid, 1 atm | 67 |
Identify the fuel with the greatest specific energy.
[1]
Identify the fuel with the greatest energy density.
[1]
Explain why the fuel with greatest specific energy is not necessarily the best fuel for a vehicle.
[1]
Suggest one environmental factor, other than carbon dioxide from combustion, that should be considered.
[1]
Question 40
The diagram shows an acidic direct methanol fuel cell.
Deduce the anode half-equation from the species shown.
[1]
State the role of oxygen at the cathode.
[1]
State one advantage and one disadvantage of methanol compared with hydrogen as a fuel-cell fuel.
[1]
Question 41
A proposed biofuel project would grow oilseed crops on land currently used for food crops. The table gives estimated annual values for the project.
| Outcome (unit) | Annual estimate |
|---|---|
| Biofuel energy produced (GJ yr⁻¹) | 240000 |
| CO₂ fixed during crop growth (t CO₂ yr⁻¹) | 18000 |
| Farming and processing emissions (t CO₂e yr⁻¹) | 12500 |
| Water use (m³ yr⁻¹) | 950000 |
| Change in food-crop output (t yr⁻¹) | -3200 |
| Change in biodiversity index (%) | -14 |
Identify one environmental benefit shown by the data.
[1]
Identify one social or ethical concern shown by the data.
[1]
Evaluate whether the project should be described as sustainable.
[1]
Question 42
Methane is used as a domestic fuel.
Write balanced equations for the complete combustion of methane and for incomplete combustion producing carbon monoxide.
[1]
Explain why methane is useful as a fuel but can present safety and health risks during combustion.
[1]
Question 43
Coal, crude oil and natural gas are major fossil fuels.
Define a fossil fuel and state why fossil fuels are non-renewable.
[1]
Compare the advantages and disadvantages of coal, crude oil and natural gas as energy sources.
[1]
Question 44
Biofuels are produced from recently living biological material.
Write balanced equations for photosynthesis and fermentation of glucose.
[1]
Discuss the advantages and disadvantages of using biofuels instead of fossil fuels.
[1]
Question 45
Hydrogen can be used in a fuel cell.
Write the two half-equations for an acidic hydrogen fuel cell.
[1]
Explain how a fuel cell differs from a primary voltaic cell and evaluate one environmental advantage and one limitation of hydrogen fuel cells.
[1]
Question 46
The graph shows the percentage of carbon converted to soot during combustion of several straight-chain alkanes under the same burner conditions.
Describe the trend shown.
[1]
Explain the trend using intermolecular forces and volatility.
[1]
Suggest one change to the burner conditions that would reduce soot formation.
[1]
Question 47
A power station is considering replacing coal with natural gas.
Calculate the mass of CO₂ produced by complete combustion of 1.00 kg of methane. Use CH₄ + 2O₂ → CO₂ + 2H₂O.
[1]
Evaluate the environmental, economic and ethical implications of replacing coal with natural gas.
[1]
Question 48
The combustion behaviour of hydrocarbons changes with chain length.
Write balanced equations for complete combustion of hexane, C₆H₁₄, and incomplete combustion of hexane producing carbon.
[1]
Explain why longer-chain hydrocarbons have a greater tendency to undergo incomplete combustion and discuss one consequence for air quality.
[1]
Question 49
Hydrogen and methanol can both be used in fuel cells.
Write the overall reactions for an acidic hydrogen fuel cell and an acidic direct methanol fuel cell.
[1]
Compare and contrast hydrogen and methanol as fuel-cell fuels, including half-equation features, storage, products and environmental considerations.
[1]
Question 50
A government plans to replace 20% of road-transport petrol with bioethanol made from maize.
Outline how carbon from atmospheric carbon dioxide can become carbon in ethanol. Include relevant equations.
[1]
Evaluate the claim that this policy will reduce climate impact without creating significant social or environmental problems.
[1]
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