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Cambridge International AS Level Chemistry

Reactions of Alkanes

Alkanes are relatively unreactive because C-C and C-H bonds are strong and essentially non-polar. Their key organic reaction in this section is free radical substitution with halogens, which occurs through a chain mechanism involving initiation, propagation and termination steps.

Alkene bonding and geometrical isomerism sit in Topic 13 and polymers in Topic 20, and are linked from these pages.

Exam Papers
Papers 1 & 2
9701/1 and 9701/2 (AS Level)
Learning Outcomes
14.1.2 – 14.1.5
3 points covered
Sub-topics
5 lessons
Revision notes available
Exam Board
Cambridge
CIE 9701 (2025-2027)

Revision Notes

5 revision notes, in the order the specification teaches them.

A radical pulling a hydrogen from a methane molecule
1

Free Radical Substitution

Revise the overall reaction type, why radicals are formed and how halogenation replaces a hydrogen atom in an alkane.

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Light splitting a halogen molecule into two radicals
2

Initiation

Learn how ultraviolet light causes homolytic fission of a halogen molecule to form two reactive halogen radicals.

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A radical used and regenerated in a cycle
3

Propagation

Review the two repeating steps that produce the organic product and regenerate a radical so the chain reaction continues.

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Two radicals joining to end the chain
4

Termination

Revise how two radicals combine to form a stable molecule, removing radicals and stopping that part of the chain.

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More and more hydrogen atoms replaced by halogen
5

Further Substitution

Learn how substitution can continue to form mixtures of products when more hydrogen atoms are replaced by halogen atoms.

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Summary Map

Download, print and revise the reactions of this topic at a glance.

Summary maps

Download, print and revise the reactions of this topic at a glance.

Illustration of a summary map: compounds joined by reaction arrows
Summary map · PDF

Alkanes Map

Cambridge International AS & A Level Chemistry · Topic 14 Hydrocarbons

Every reaction on one A4 page: reagents, conditions and reaction type for each arrow, colour coded, with the key tests.

Download the map4 reactions · A4 portrait · print ready
Illustration of a summary map: compounds joined by reaction arrows
Summary map · PDF

Alkanes Summary Map

Cambridge International AS & A Level Chemistry · 14.1 Alkanes

The whole section on one A4 page: cracking and hydrogenation, combustion, engine pollutants and the catalytic converter, the unreactivity of alkanes, with the free-radical mechanism for ethane in a table.

Download the map6 key ideas + the mechanism · A4 portrait · print ready

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Multiple-choice papers on this topic, marked the moment you submit.

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Written, drawn and worked exam practice on this topic.

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Revision Game

Match reagents to products, free, with your board's reagents and conditions.

Illustration of memory game cards, two turned face up as a matching pairFree

Revision Game: Alkanes

Turn the cards over two at a time: match reagents to what they make, and find how each product is made.

A free memory game on the reactions in this topic, with your board's reagents, conditions and spec points.

  • Two ways to playMatch each set of reagents to what the reaction makes, or see a product and find the reactant and reagents that make it.
  • Drawn the way the exam draws themEvery structure is drawn in ChemDraw, with the reagents and conditions your exam board asks for.
  • It countsRounds earn XP and keep your streak going, and every correct match shows in your KASP analytics, apart from your marks.

Study Cards

Pick a deck, then turn each card to check what you remember.

Specification

Every specification point in this topic, in the exam board's own words. Rate how confident you are with each one.

Official Cambridge documentsSyllabus (opens the Cambridge website in a new tab)

Cambridge no longer issues a data booklet: the data you need are given in each question, and the syllabus has a Data section.

Self-assessment · 24 points

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1.3.9

  1. 1.3.9

    describe a free radical as a species with one or more unpaired electrons

    Revise

12.1.3

  1. a

    state and explain the natural occurrences of oxides of nitrogen

    Revise
  2. b

    state and explain the man-made occurrences of oxides of nitrogen

    Revise

13.2.1

  1. c i

    interpret and use the term homolytic fission

    Revise
  2. d ii

    interpret and use the term initiation

    Revise
  3. d iii

    interpret and use the term propagation

    Revise
  4. d iv

    interpret and use the term termination

    Revise

14.1.1

  1. a

    recall the reaction (reagents and conditions) by which alkanes can be produced: addition of hydrogen to an alkene in a hydrogenation reaction, H2(g) and Pt/Ni catalyst and heat

    Revise
  2. b

    recall the reaction (reagents and conditions) by which alkanes can be produced: cracking of a longer chain alkane, heat with Al2O3

    Revise

14.1.2

  1. a i

    describe the complete combustion of alkanes

    Revise
  2. a ii

    describe the incomplete combustion of alkanes

    Revise
  3. b i

    describe the free-radical substitution of alkanes by Cl2 in the presence of ultraviolet light, as exemplified by the reactions of ethane

    Revise
  4. b ii

    describe the free-radical substitution of alkanes by Br2 in the presence of ultraviolet light, as exemplified by the reactions of ethane

    Revise

14.1.3

  1. a

    describe the mechanism of free-radical substitution with reference to the initiation step

    Revise
  2. b

    describe the mechanism of free-radical substitution with reference to the propagation steps

    Revise
  3. c

    describe the mechanism of free-radical substitution with reference to the termination steps

    Revise

14.1.4

  1. 14.1.4

    suggest how cracking can be used to obtain more useful alkanes and alkenes of lower Mr from heavier crude oil fractions

    Revise

14.1.5

  1. a

    understand the general unreactivity of alkanes, including towards polar reagents, in terms of the strength of the C–H bonds

    Revise
  2. b

    understand the general unreactivity of alkanes, including towards polar reagents, in terms of the relative lack of polarity of the C–H bonds

    Revise

14.1.6

  1. a

    recognise the environmental consequences of carbon monoxide arising from the combustion of alkanes in the internal combustion engine

    Revise
  2. b

    recognise the environmental consequences of oxides of nitrogen arising from the combustion of alkanes in the internal combustion engine

    Revise
  3. c

    recognise the environmental consequences of unburnt hydrocarbons arising from the combustion of alkanes in the internal combustion engine

    Revise
  4. d

    recognise the catalytic removal of carbon monoxide, oxides of nitrogen and unburnt hydrocarbons arising from the combustion of alkanes in the internal combustion engine

    Revise

14.2.1

  1. c

    recall the reaction (including reagents and conditions) by which alkenes can be produced: cracking of a longer chain alkane

    Revise