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Topic R1.3 · HL only

Energy from fuels: notes and practice questions

2 min read Jump to 4 practice questions
Summary
  • This topic covers the higher level extension of energy from fuels.
  • The IB Chemistry guide explicitly states "Additional higher level: None for Reactivity 1.3".
  • Therefore, there is no specific additional content for Higher Level students in this topic beyond the Standard Level material.

How it is examined

Balancing a combustion equation is a 1-mark part and it must be balanced: mark scheme instruction 16 says a word equation or an unbalanced equation earns nothing unless the Notes say otherwise. Fuel cell half-equations come as a pair worth [2]. May 2025 HL Paper 2 TZ1 asked for both electrode half-equations of a molten carbonate fuel cell for [2], accepting a doubling of all coefficients in the cathode equation, then asked in one mark why it is described as environmentally friendly. The evaluative parts on biofuels and fossil fuels are 2 to 3 marks and want a balanced argument, not a list of advantages.

Given in the booklet

Enthalpies of combustion (HL). Nothing else specific. Balancing a combustion equation is recall, and half-equations for fuel cells are deduced, not looked up.

Key ideas
  • 1.3.1 Reactive metals, non-metals and organic compounds undergo combustion reactions when heated in oxygen. Students deduce equations for combustion reactions, including hydrocarbons and alcohols.
  • 1.3.2 Incomplete combustion of organic compounds, especially hydrocarbons, leads to the production of carbon monoxide and carbon. Students deduce equations for the incomplete combustion of hydrocarbons and alcohols.
  • 1.3.3 Fossil fuels include coal, crude oil and natural gas, which have different advantages and disadvantages. Students evaluate the amount of carbon dioxide added to the atmosphere when different fuels burn, and understand the link between carbon dioxide levels and the greenhouse effect.
  • 1.3.4 Biofuels are produced from the biological fixation of carbon over a short period of time through photosynthesis. Students understand the difference between renewable and non-renewable energy sources and consider the advantages and disadvantages of biofuels.
Not assessed

The use of proton exchange membranes will not be assessed. The fuel cell is treated at the level of half-equations and energy conversion, not membrane chemistry.

Guiding questions

  • What are the challenges of using chemical energy to address our energy needs?

Linking questions

  • Reactivity 2.2 Why is high activation energy often considered to be a useful property of a fuel?
  • Reactivity 3.2 Which species are the oxidizing and reducing agents in a combustion reaction? What are the main differences between a fuel cell and a primary (voltaic) cell?
  • Reactivity 2.1 How does limiting the supply of oxygen in combustion affect the products and increase health risks?
  • Structure 3.2 Why do larger hydrocarbons have a greater tendency to undergo incomplete combustion? (HL) Why is carbon dioxide described as a greenhouse gas?
  • Nature of science, Reactivity 3.2 What are some of the environmental, economic, ethical and social implications of burning fossil fuels?
  • Inquiry 2 What might be observed when a fuel such as methane is burned in a limited supply of oxygen?

Practice questions

4 questions · 1 easy · 3 medium
Showing 4 of 4

Question 1

EasyPaper 1A · calculator1 mark

What is the sum of the coefficients when the equation for the complete combustion of propan-1-ol, C3H7OH\text{C}_3\text{H}_7\text{OH}, is balanced using the smallest whole numbers?

A. 13

B. 23

C. 25

D. 26

Question 2

MediumPaper 1A · calculator1 mark

Which half-equation represents the reaction occurring at the anode of a hydrogen fuel cell with an alkaline electrolyte?

A. H2(g)+2OH−(aq)→2H2O(l)+2e−\text{H}_2\text{(g)} + 2\text{OH}^-\text{(aq)} \rightarrow 2\text{H}_2\text{O(l)} + 2\text{e}^-

B. O2(g)+2H2O(l)+4e−→4OH−(aq)\text{O}_2\text{(g)} + 2\text{H}_2\text{O(l)} + 4\text{e}^- \rightarrow 4\text{OH}^-\text{(aq)}

C. H2(g)→2H+(aq)+2e−\text{H}_2\text{(g)} \rightarrow 2\text{H}^+\text{(aq)} + 2\text{e}^-

D. 2H2O(l)+2e−→H2(g)+2OH−(aq)2\text{H}_2\text{O(l)} + 2\text{e}^- \rightarrow \text{H}_2\text{(g)} + 2\text{OH}^-\text{(aq)}

Question 3

MediumPaper 1B · calculator3 marks
(a)

Ethanol, C2H5OH\text{C}_2\text{H}_5\text{OH}, is a biofuel commonly blended with gasoline. The equation for its complete combustion is:

C2H5OH (l)+3O2 (g)→2CO2 (g)+3H2O (l)ΔH⊖=−1367 kJ mol−1\text{C}_2\text{H}_5\text{OH}\,(\text{l}) + 3\text{O}_2\,(\text{g}) \rightarrow 2\text{CO}_2\,(\text{g}) + 3\text{H}_2\text{O}\,(\text{l}) \quad \Delta H^\ominus = -1367\text{ kJ}\text{ mol}^{-1}

(a) Calculate the specific energy of ethanol, in kJ g−1\text{kJ}\text{ g}^{-1}.

[1]
(b)

(b) Calculate the mass of carbon dioxide, in g\text{g}, produced per megajoule (1.00×103 kJ1.00 \times 10^3\text{ kJ}) of energy released by the complete combustion of ethanol.

[2]

Question 4

MediumPaper 2 · calculator2 marks

Explain why decane, C10H22\text{C}_{10}\text{H}_{22}, burns with a smoky yellow flame in air, whereas methane, CH4\text{CH}_4, burns with a clean blue flame.

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What does Energy from fuels cover in IB Chemistry?

This topic covers the higher level extension of energy from fuels. The IB Chemistry guide explicitly states "Additional higher level: None for Reactivity 1.3". Therefore, there is no specific additional content for Higher Level students in this topic beyond the Standard Level material.

Is Energy from fuels SL or HL?

Energy from fuels is HL only. SL students are not examined on it.

How do I revise Energy from fuels for IB Chemistry?

Start from the core idea: this topic covers the higher level extension of energy from fuels. In the exam: balancing a combustion equation is a 1-mark part and it must be balanced: mark scheme instruction 16 says a word equation or an unbalanced equation earns nothing unless the Notes say otherwise. Fuel cell half-equations come as a pair worth [2]. Then practise exam-style questions, easiest first, writing out every step of your working before you check it.

How does FourtyFive help me practise Energy from fuels?

FourtyFive has 4 Energy from fuels questions. Every answer you write is marked mark by mark, IB-style, and you see where each mark was won or lost. Every part has a hint, the AI tutor helps you through the step you are stuck on, and your Study Profile picks what to practise next.

Is FourtyFive free for Energy from fuels practice?

Yes. A free account gives you 50 marked answers a month, and you do not need a card to sign up.

Can I handwrite Energy from fuels answers on an iPad?

Yes. In the FourtyFive iPad app you write your working by hand with Apple Pencil, the way you would on paper, and it is marked the same way.

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