IB Chemistry Quiz: Apply Energy From Fuels
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Apply Energy From FuelsQuestion 1 of 20

Which statement correctly compares the complete combustion of 1.0 mole of methane (CH₄) and the incomplete combustion of 1.0 mole of methane to produce carbon monoxide and water?

Incomplete combustion releases more energy per mole of methane as it produces water, a very stable molecule.
Complete combustion produces carbon dioxide, a toxic gas that binds to hemoglobin, while incomplete combustion is harmless.
Incomplete combustion requires a greater amount of oxygen per mole of methane than complete combustion.
Complete combustion is a more exothermic process and produces carbon dioxide, a greenhouse gas, while incomplete combustion produces toxic carbon monoxide.
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IB Chemistry Quiz

IB Chemistry Quiz: Apply Energy From Fuels

Practice Apply Energy From Fuels in IB Chemistry with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Apply Energy From Fuels, giving you a quick way to practice the rules, question types, and explanations that matter most for IB Chemistry.

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Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

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Question 1

Which statement correctly compares the complete combustion of 1.0 mole of methane (CH₄) and the incomplete combustion of 1.0 mole of methane to produce carbon monoxide and water?

  1. Incomplete combustion releases more energy per mole of methane as it produces water, a very stable molecule.
  2. Complete combustion produces carbon dioxide, a toxic gas that binds to hemoglobin, while incomplete combustion is harmless.
  3. Incomplete combustion requires a greater amount of oxygen per mole of methane than complete combustion.
  4. Complete combustion is a more exothermic process and produces carbon dioxide, a greenhouse gas, while incomplete combustion produces toxic carbon monoxide. (correct answer)
Explanation: Complete combustion (CH₄ + 2O₂ → CO₂ + 2H₂O) releases more energy (is more exothermic) than incomplete combustion (CH₄ + 1.5O₂ → CO + 2H₂O) because the formation of C=O bonds in CO₂ is energetically more favorable than the formation of the C≡O bond in CO. Complete combustion produces CO₂, a greenhouse gas. Incomplete combustion produces CO, which is toxic as it binds irreversibly to hemoglobin.

Question 2

Given the following standard enthalpies of combustion (ΔHc°): CH₄(g) = -890 kJ mol⁻¹; C₈H₁₈(l) = -5470 kJ mol⁻¹.

Which fuel produces a smaller mass of CO₂ per MJ of energy released?

  1. Octane, because it is a larger molecule and burns more efficiently, releasing less CO₂ per unit energy.
  2. Methane, because for every mole of fuel burned, it produces only one mole of CO₂.
  3. Methane, because the ratio of mass of CO₂ produced to energy released is lower than that for octane. (correct answer)
  4. Both fuels produce the same mass of CO₂ per MJ, as they are both hydrocarbons.
Explanation: We need to calculate the mass of CO₂ (M = 44.01 g mol⁻¹) per unit of energy. For Methane (CH₄): 1 mole produces 1 mole CO₂ (44.01 g) and 890 kJ of energy. Mass/Energy = 44.01 g / 0.890 MJ ≈ 49.4 g CO₂/MJ. For Octane (C₈H₁₈): 1 mole produces 8 moles CO₂ (8 * 44.01 g = 352.08 g) and 5470 kJ of energy. Mass/Energy = 352.08 g / 5.470 MJ ≈ 64.4 g CO₂/MJ. Methane produces a smaller mass of CO₂ per MJ of energy.

Question 3

The standard enthalpy of combustion for ethanol (C₂H₅OH) is -1367 kJ mol⁻¹ and for octane (C₈H₁₈) is -5470 kJ mol⁻¹.

Based on the provided data, which statement correctly compares the energy produced by these two fuels?

  1. Octane produces more energy per mole, and also produces more energy per gram, than ethanol. (correct answer)
  2. Ethanol produces more energy per gram than octane because it contains an oxygen atom, which aids combustion.
  3. Octane produces more energy per mole, but ethanol produces more energy per gram.
  4. Both fuels produce approximately the same amount of energy per gram since they are both liquid hydrocarbon-based fuels.
Explanation: To compare energy per gram, we must calculate the specific energy. M(C₂H₅OH) ≈ 46.07 g mol⁻¹. Specific energy = 1367 kJ / 46.07 g ≈ 29.7 kJ g⁻¹. M(C₈H₁₈) ≈ 114.26 g mol⁻¹. Specific energy = 5470 kJ / 114.26 g ≈ 47.9 kJ g⁻¹. Therefore, octane produces more energy per mole (-5470 vs -1367 kJ mol⁻¹) and also more energy per gram (47.9 vs 29.7 kJ g⁻¹).

Question 4

What volume of carbon dioxide, in dm³, measured at Standard Temperature and Pressure (STP), is produced by the complete combustion of 11.5 g of ethanol, C₂H₅OH(l)? (Molar mass of ethanol ≈ 46.0 g mol⁻¹; Molar volume of a gas at STP = 22.7 dm³ mol⁻¹)

  1. 11.4 dm³ (correct answer)
  2. 5.68 dm³
  3. 22.7 dm³
  4. 45.4 dm³
Explanation: First, calculate the moles of ethanol: n = mass / M = 11.5 g / 46.0 g mol⁻¹ = 0.250 mol. Next, write the balanced equation: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O. The mole ratio of ethanol to carbon dioxide is 1:2. Therefore, moles of CO₂ produced = 0.250 mol C₂H₅OH × (2 mol CO₂ / 1 mol C₂H₅OH) = 0.500 mol CO₂. Finally, calculate the volume of CO₂ at STP: V = n × Vm = 0.500 mol × 22.7 dm³ mol⁻¹ = 11.35 dm³, which is approximately 11.4 dm³.

Question 5

What is the ultimate origin of the chemical energy released when fossil fuels are burned?

  1. Solar energy captured via photosynthesis by ancient plants and microorganisms. (correct answer)
  2. Geothermal energy from the Earth's core, which heated and pressurized ancient organic matter.
  3. Kinetic energy from the Earth's rotation that was converted into chemical bonds under pressure.
  4. Nuclear energy from radioactive isotopes that became trapped within the organic deposits.
Explanation: Fossil fuels are formed from the remains of ancient living organisms (plants, algae, plankton). These organisms originally captured energy from the sun through photosynthesis, converting light energy into chemical energy stored in complex organic molecules (biomass). Over millions of years, heat and pressure transformed this stored chemical energy into the forms we know as coal, oil, and natural gas. The geothermal energy provided the conditions for transformation but was not the original source of the stored chemical energy.

Question 6

A fuel cell uses hydrogen gas with an energy density of 120 MJ/kg, but the overall system efficiency is only 45% due to conversion losses. A gasoline engine has fuel with energy density of 44 MJ/kg and operates at 25% efficiency. If both systems must provide 500 MJ of useful energy output, what is the difference in fuel mass required, and which factor most significantly affects this comparison?

  1. Fuel cell requires 9.26 kg, gasoline requires 45.45 kg; difference = 36.19 kg; energy density is the most significant factor (correct answer)
  2. Fuel cell requires 9.26 kg, gasoline requires 45.45 kg; difference = 36.19 kg; system efficiency is the most significant factor
  3. Fuel cell requires 11.11 kg, gasoline requires 50.00 kg; difference = 38.89 kg; energy density is the most significant factor
  4. Fuel cell requires 11.11 kg, gasoline requires 50.00 kg; difference = 38.89 kg; system efficiency is the most significant factor
Explanation: For fuel cell: Energy input needed = 500 MJ ÷ 0.45 = 1111.1 MJ. Mass = 1111.1 ÷ 120 = 9.26 kg. For gasoline: Energy input needed = 500 MJ ÷ 0.25 = 2000 MJ. Mass = 2000 ÷ 44 = 45.45 kg. Difference = 36.19 kg. To determine the most significant factor: If only energy density differed (120 vs 44 MJ/kg at same efficiency), mass ratio would be 44/120 = 0.37. If only efficiency differed (45% vs 25% with same energy density), mass ratio would be 25/45 = 0.56. Since 0.37 < 0.56, energy density has the larger effect on fuel mass requirements.

Question 7

A research team develops a new biofuel with formula C8H16O2\text{C}_8\text{H}_{16}\text{O}_2 and determines its standard enthalpy of combustion experimentally. In a bomb calorimeter with heat capacity 12.5 kJ/°C, combustion of 0.755 g of this fuel increases the temperature by 3.84°C. Calculate the energy density of this biofuel and compare it to biodiesel (typical energy density 37 MJ/kg). What percentage of biodiesel's energy density does this new fuel achieve?

  1. Energy density = 63.7 MJ/kg; achieves 172% of biodiesel's energy density, indicating superior performance per unit mass (correct answer)
  2. Energy density = 63.7 MJ/kg; achieves 58% of biodiesel's energy density, indicating lower performance per unit mass
  3. Energy density = 35.2 MJ/kg; achieves 95% of biodiesel's energy density, indicating comparable performance per unit mass
  4. Energy density = 35.2 MJ/kg; achieves 105% of biodiesel's energy density, indicating slightly superior performance per unit mass
Explanation: Heat released = 12.5 kJ/°C × 3.84°C = 48.0 kJ. Mass of fuel = 0.755 g. Energy density = 48.0 kJ ÷ 0.755 g = 63.6 kJ/g = 63.6 MJ/kg. Compared to biodiesel: (63.6 ÷ 37) × 100% = 172%. The new biofuel achieves 172% of biodiesel's energy density. Choice B incorrectly calculates the percentage as 58% (perhaps calculating 37/63.6). Choices C and D use an incorrect energy density calculation, possibly from an error in unit conversion or calculation method.

Question 8

A student compares the energy density of three fuels by measuring the temperature change when 2.50 g of each fuel is completely combusted in a calorimeter containing 150.0 g of water. Fuel A increases the water temperature by 18.2°C, Fuel B by 24.6°C, and Fuel C by 21.8°C. If the specific heat capacity of water is 4.18 J g−1°C−14.18 \text{ J g}^{-1} \text{°C}^{-1} and heat losses are negligible, which statement correctly ranks the fuels by energy density and identifies the most suitable fuel for a portable camping stove where weight is the primary concern?

  1. Energy density: B > C > A; Fuel B is most suitable because it has the highest energy density and will provide the longest burning time per gram (correct answer)
  2. Energy density: A > C > B; Fuel A is most suitable because it burns most efficiently and produces the least waste heat per gram
  3. Energy density: B > C > A; Fuel A is most suitable because it has lower energy density and therefore burns more safely in portable equipment
  4. Energy density: C > B > A; Fuel C is most suitable because it provides optimal balance between energy output and combustion temperature control
Explanation: First, calculate energy released: Fuel A: q=150.0×4.18×18.2=11,400 Jq = 150.0 \times 4.18 \times 18.2 = 11,400 \text{ J}; Fuel B: q=150.0×4.18×24.6=15,400 Jq = 150.0 \times 4.18 \times 24.6 = 15,400 \text{ J}; Fuel C: q=150.0×4.18×21.8=13,700 Jq = 150.0 \times 4.18 \times 21.8 = 13,700 \text{ J}. Energy density per gram: A = 4,560 J/g, B = 6,160 J/g, C = 5,480 J/g. Therefore B > C > A. For portable use where weight matters, highest energy density (B) provides most energy per unit mass. Choice B incorrectly ranks energy density. Choice C correctly ranks but incorrectly suggests lower energy density is better for portability. Choice D incorrectly ranks the fuels.

Question 9

An automotive engineer compares two fuel injection strategies for ethanol (C2H5OH\text{C}_2\text{H}_5\text{OH}). Strategy A injects fuel at stoichiometric air-fuel ratio, while Strategy B uses 10% excess air. The standard enthalpy of combustion of ethanol is -1367 kJ/mol. If the engine operates at 30% thermal efficiency under both conditions, but Strategy B reduces combustion temperature by 80°C, which strategy provides better fuel economy and why?

  1. Strategy A provides better fuel economy because stoichiometric combustion maximizes energy release per mole of fuel consumed in the reaction
  2. Strategy A provides better fuel economy because excess air in Strategy B dilutes the fuel mixture and reduces the effective energy density
  3. Strategy B provides better fuel economy because lower combustion temperature reduces heat losses to the cylinder walls and cooling system
  4. Both strategies provide identical fuel economy because thermal efficiency and enthalpy of combustion remain constant regardless of air-fuel ratio (correct answer)
Explanation: The enthalpy of combustion (-1367 kJ/mol) is a thermodynamic property that depends only on the initial and final states, not the combustion conditions. Both strategies completely combust ethanol to CO₂ and H₂O, so the energy released per mole of fuel is identical. The thermal efficiency (30%) is stated to be the same for both conditions. Therefore, the useful work output per mole of fuel is identical (0.30 × 1367 = 410 kJ/mol). Excess air affects combustion temperature and emissions, but not the fundamental energy conversion. Choice A incorrectly suggests energy release changes with air ratio. Choice B incorrectly relates air dilution to energy density. Choice C incorrectly assumes lower temperature improves efficiency when thermal efficiency is given as constant.

Question 10

The claim that bioethanol is a 'carbon-neutral' fuel is often considered an oversimplification. What is the main reason for this?

  1. The combustion of bioethanol produces carbon monoxide and soot, which are not absorbed by plants.
  2. The energy required for farming, distillation, and transportation of bioethanol is often derived from fossil fuels. (correct answer)
  3. The amount of carbon dioxide absorbed by the plants during photosynthesis is significantly less than the amount released during combustion.
  4. The water produced during the combustion of bioethanol contributes to the greenhouse effect more than carbon dioxide.
Explanation: While it is true that the CO₂ released during combustion is theoretically balanced by the CO₂ absorbed during the plant's growth, the entire life cycle is not carbon-neutral. Significant energy input from fossil fuels is required for planting, harvesting, fermentation, distillation, and transportation, which adds a net amount of CO₂ to the atmosphere.

Question 11

Incomplete combustion of propane (C₃H₈) produces carbon monoxide and water as the only products. What is the sum of all integer coefficients when the equation for this reaction is balanced?

  1. 13
  2. 15
  3. 21
  4. 23 (correct answer)
Explanation: The unbalanced equation is C₃H₈ + O₂ → CO + H₂O. Balancing C and H gives C₃H₈ + O₂ → 3CO + 4H₂O. The right side has 3 + 4 = 7 oxygen atoms. So, 3.5 O₂ molecules are needed: C₃H₈ + 3.5O₂ → 3CO + 4H₂O. To get integer coefficients, multiply the entire equation by 2: 2C₃H₈ + 7O₂ → 6CO + 8H₂O. The sum of the coefficients is 2 + 7 + 6 + 8 = 23.

Question 12

In a direct methanol fuel cell (DMFC) with an acidic electrolyte, what is the correct half-equation for the reaction at the anode?

  1. O₂(g) + 4H⁺(aq) + 4e⁻ → 2H₂O(l)
  2. CH₃OH(l) + H₂O(l) → CO₂(g) + 6H⁺(aq) + 6e⁻ (correct answer)
  3. CO₂(g) + 6H⁺(aq) + 6e⁻ → CH₃OH(l) + H₂O(l)
  4. CH₃OH(l) + 3O₂(g) → 2CO₂(g) + 4H₂O(l)
Explanation: The anode is the site of oxidation. Methanol (CH₃OH) is the fuel and is oxidized to carbon dioxide (CO₂). Balancing the atoms and charge in an acidic medium gives the half-equation: CH₃OH(l) + H₂O(l) → CO₂(g) + 6H⁺(aq) + 6e⁻. Choice A is the cathode reaction. Choice C is the reverse of the anode reaction (reduction). Choice D is an unbalanced overall combustion equation, not a half-equation.

Question 13

Which statement best describes the molecular mechanism by which gases like CO₂ contribute to the enhanced greenhouse effect?

  1. They react with ozone in the stratosphere, allowing more high-energy solar radiation to reach the Earth's surface.
  2. They are good absorbers of incoming high-frequency ultraviolet radiation, which they re-radiate as heat.
  3. The bonds within these molecules vibrate upon absorbing outgoing low-frequency infrared radiation, which is then re-radiated in all directions. (correct answer)
  4. They form a reflective layer in the upper atmosphere that prevents heat from escaping into space, similar to the glass of a greenhouse.
Explanation: Greenhouse gases do not absorb incoming UV radiation (that's ozone's role) or form a simple reflective layer. The mechanism involves the absorption of specific frequencies of outgoing infrared (IR) radiation from the Earth's surface. This absorbed energy causes the covalent bonds in the gas molecules (like the C=O bonds in CO₂) to vibrate. The excited molecules then re-radiate this energy as IR radiation in all directions, including back towards the Earth's surface, thus trapping heat in the lower atmosphere.

Question 14

Hydrogen is often cited as a clean fuel. What is a primary reason why its widespread use is currently limited by challenges in production?

  1. The electrolysis of water to produce hydrogen is extremely inefficient, converting less than 10% of electrical energy into chemical energy.
  2. The vast majority of commercial hydrogen is produced from the steam reforming of methane, a process that consumes fossil fuels and releases carbon dioxide. (correct answer)
  3. Hydrogen gas is not naturally available on Earth and must be synthesized in nuclear reactors, a process which is costly and produces radioactive waste.
  4. The H-H bond is the strongest single bond known, making it impossible to produce hydrogen gas through chemical reactions at reasonable temperatures.
Explanation: Although 'green' hydrogen can be produced by electrolysis of water using renewable energy, this is currently expensive and not widespread. The most common and cheapest method for producing H₂ is the steam reforming of natural gas (methane): CH₄(g) + H₂O(g) → CO(g) + 3H₂(g). This process uses a fossil fuel as a feedstock and also releases CO₂, undermining the 'clean' aspect of the hydrogen fuel cycle.

Question 15

What distinguishes coal from natural gas in terms of chemical composition and environmental impact upon combustion?

  1. Coal is a pure form of carbon, while natural gas is a mixture of hydrocarbons; both produce only CO₂ and H₂O when burned.
  2. Natural gas contains more sulfur impurities than coal, leading to greater acid rain when it is burned.
  3. Coal has a higher hydrogen-to-carbon ratio than natural gas, resulting in less CO₂ production per unit of energy.
  4. Coal is a complex solid mixture containing sulfur impurities, leading to SO₂ emissions and acid rain; natural gas is primarily CH₄ with fewer impurities. (correct answer)
Explanation: Coal is not pure carbon but a complex solid containing various elements, notably sulfur. Burning coal releases sulfur dioxide (SO₂), a primary precursor to acid rain. Natural gas is mostly methane (CH₄) and is typically processed to remove most sulfur compounds. Therefore, burning natural gas is significantly cleaner in terms of SO₂ emissions. Also, methane's high hydrogen-to-carbon ratio means it produces less CO₂ per unit of energy than coal.

Question 16

What is the correct classification of hydrogen fuel and its justification?

  1. It is a primary renewable fuel because it can be produced from water, which is abundant and part of a natural cycle.
  2. It is a primary non-renewable fuel because most of it is currently produced from methane, a fossil fuel.
  3. It is a secondary energy carrier because it must be produced using energy from another source, which may be renewable or non-renewable. (correct answer)
  4. It is a secondary renewable fuel because its only combustion product is water, which can be recycled.
Explanation: Hydrogen gas (H₂) is not found in large quantities naturally on Earth; it must be manufactured. Therefore, it is not a primary energy source. It is an energy carrier, meaning it is a way to store and transport energy that has been generated from a primary source (like natural gas, solar, or nuclear). Its classification as renewable or non-renewable depends entirely on the primary energy source used to produce it.

Question 17

What is the primary reason carbon monoxide (CO) is considered a more immediate health hazard than carbon dioxide (CO₂) when produced by indoor fuel combustion?

  1. CO is a much more potent greenhouse gas than CO₂, leading to rapid atmospheric heating.
  2. CO is acidic and causes severe damage to lung tissue upon inhalation, while CO₂ is physiologically inert.
  3. CO binds strongly and preferentially to hemoglobin in the blood, preventing the transport of oxygen to tissues. (correct answer)
  4. CO is significantly denser than air and accumulates at floor level, while CO₂ is lighter than air and dissipates quickly.
Explanation: The acute toxicity of carbon monoxide stems from its effect on the circulatory system. The CO molecule has a similar size and shape to O₂ and can fit into the same binding site on hemoglobin in red blood cells. However, its affinity for hemoglobin is over 200 times greater than that of oxygen. It binds effectively irreversibly, forming carboxyhemoglobin and preventing the blood from carrying oxygen from the lungs to the body's tissues, leading to asphyxiation.

Question 18

In the operation of a direct methanol fuel cell (DMFC) with an acidic electrolyte, which statement correctly describes the process at the cathode?

  1. Oxygen from the air is reduced to form water, and its oxidation state changes from 0 to -2. (correct answer)
  2. Methanol is reduced to carbon dioxide, and the oxidation state of carbon increases.
  3. Water is oxidized to form oxygen gas and hydrogen ions, with oxygen's oxidation state changing from -2 to 0.
  4. Hydrogen ions are reduced to form hydrogen gas, with hydrogen's oxidation state changing from +1 to 0.
Explanation: The cathode is the site of reduction. In a DMFC (and most fuel cells), the oxidant is oxygen, typically from the air. In an acidic medium, oxygen is reduced to water according to the half-equation: O₂(g) + 4H⁺(aq) + 4e⁻ → 2H₂O(l). In this process, the oxidation state of oxygen changes from 0 in O₂ to -2 in H₂O. Methanol is oxidized at the anode, not the cathode.

Question 19

What is the primary reason that a hydrogen-oxygen fuel cell is theoretically more efficient at producing useful work than an internal combustion engine?

  1. The O-H bonds formed in the water product are much stronger than the C-H bonds in gasoline.
  2. A fuel cell converts chemical potential energy directly into electrical energy, bypassing the production of thermal energy as an intermediate step. (correct answer)
  3. Hydrogen is a gas at room temperature, allowing it to mix with oxygen more effectively than liquid gasoline.
  4. The overall reaction in a fuel cell has a more negative Gibbs free energy change than the combustion of gasoline.
Explanation: The high efficiency of a fuel cell stems from its direct conversion of chemical energy to electrical energy. An internal combustion engine follows the path: chemical energy → thermal energy → mechanical energy. Each conversion step, particularly the thermal to mechanical step, is subject to significant energy loss as waste heat, as described by the laws of thermodynamics (e.g., Carnot efficiency limits).

Question 20

Which of these energy sources is correctly described as a renewable fuel?

  1. Natural gas, because new deposits are continuously being formed within the Earth's crust.
  2. Uranium, because a small amount can generate a vast quantity of energy for many years.
  3. Hydrogen produced from the electrolysis of water using geothermal power. (correct answer)
  4. Hydrogen produced from the steam reforming of methane.
Explanation: A renewable fuel is derived from a source that is not depleted with use or can be replenished within a human lifespan. Natural gas and uranium are non-renewable. Hydrogen is an energy carrier, and its renewability depends on its production method. Hydrogen from steam reforming of methane (a fossil fuel) is non-renewable. Hydrogen produced via electrolysis is only renewable if the electricity for the process comes from a renewable source, such as geothermal, solar, or wind power.