Who this is for: Cambridge IGCSE Coordinated Science (0654) students who want alkanes — saturated hydrocarbons, combustion and substitution — to become reliable marks instead of formula-matching without understanding reactivity.
What query it owns: how to understand and revise alkanes in Cambridge IGCSE Coordinated Science.
Why this is safe: this page owns the alkanes revision-guide angle, while Tutopiya’s Alkanes subtopic page owns the learning resource and the free Alkanes quiz owns the practice.

Alkanes are saturated hydrocarbons — they contain only carbon–carbon single bonds and carbon–hydrogen bonds. Cambridge IGCSE Coordinated Science (0654) expects you to name the first four alkanes, state the general formula CₙH₂ₙ₊₂, describe combustion reactions, and explain why alkanes are unreactive compared with alkenes. This guide covers the syllabus definitions, reaction equations examiners reward, and the question types that appear every year.

Key takeaways

• Alkanes are saturated — all C–C bonds are single bonds; general formula CₙH₂ₙ₊₂.
• First four alkanes: methane (CH₄), ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀).
• Alkanes undergo complete combustion in oxygen → CO₂ + H₂O (+ energy).
• Alkanes are generally unreactive because C–C and C–H bonds are strong and non-polar.
• Substitution with chlorine (in UV light) replaces H with Cl — e.g. methane → chloromethane + HCl.

What are alkanes in Cambridge IGCSE Coordinated Science?

Alkanes form the simplest homologous series of hydrocarbons. Their saturated structure makes them relatively unreactive — the main reactions tested are combustion (as fuels) and halogen substitution in sunlight. Alkanes are major components of natural gas (methane) and LPG (propane, butane). Examiners test naming, formulas, combustion equations and the reason for alkanes’ low reactivity.

Read the full notes on Tutopiya’s Alkanes subtopic page before attempting questions.

The core ideas you must master

Idea	What it means	How the exam uses it
Saturated	Only C–C single bonds	”State why alkanes are saturated.”
General formula	CₙH₂ₙ₊₂	”Give the formula of the alkane with 3 carbons.”
Combustion	Reaction with oxygen	”Write the combustion equation for methane.”
Unreactive	Strong C–H bonds, non-polar	”Explain why alkanes do not decolourise bromine.”
Substitution	H replaced by halogen	”Describe the reaction of methane with chlorine.”

The first four alkanes

Alkane	Formula	Structural idea	Common source
Methane	CH₄	1 carbon, 4 H	Natural gas
Ethane	C₂H₆	2 carbons, 6 H	Natural gas (minor)
Propane	C₃H₈	3 carbons, 8 H	LPG
Butane	C₄H₁₀	4 carbons, 10 H	LPG, cigarette lighters

Combustion of alkanes

Alkane	Complete combustion equation	Products
Methane	CH₄ + 2O₂ → CO₂ + 2H₂O	CO₂ + H₂O
Ethane	2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O	CO₂ + H₂O
Propane	C₃H₈ + 5O₂ → 3CO₂ + 4H₂O	CO₂ + H₂O

Incomplete combustion (limited O₂): produces carbon monoxide (CO) and/or carbon (soot) as well as H₂O.

Why alkanes are unreactive

• C–C and C–H bonds are strong and non-polar.
• No functional group (unlike alkenes’ C=C or alcohols’ –OH) to undergo addition.
• Alkanes do not decolourise bromine water (unlike alkenes).
• Main reactions: combustion and substitution with halogens in UV light.

Alkanes in past-paper wording

Command word	What the question wants	Typical stem
State formula	Molecular formula from name	”State the formula of butane.”
Write equation	Combustion products	”Write the equation for methane combustion.”
Explain	Why unreactive / no bromine test	”Explain why ethane does not decolourise bromine water.”
Name	Systematic name from formula	”Name the alkane C₃H₈.”
Describe	Substitution reaction	”Describe the reaction of ethane with chlorine.”

Worked exam-style stems

1. “Write a word equation for the complete combustion of methane.” Methane + oxygen → carbon dioxide + water. Reward: correct reactants and products.
2. “Explain why alkanes are described as saturated hydrocarbons.” They contain only carbon and hydrogen, and all carbon–carbon bonds are single bonds (no double bonds). Reward: C and H only + single C–C bonds.
3. “Explain why propane does not decolourise bromine water.” Propane is an alkane with no C=C double bond; bromine water tests for unsaturation (alkenes), and alkanes do not react under normal conditions. Reward: no double bond + alkanes unreactive with bromine water.

Practise on the Alkanes quiz.

How alkanes connect to the syllabus

Alkanes link to Fuels (hydrocarbon combustion), Homologous Series (general formula CₙH₂ₙ₊₂) and Alkenes (contrast saturated vs unsaturated). The Cambridge IGCSE Coordinated Science resource hub links every Organic Chemistry subtopic.

Common mistakes students make

• Confusing ethane (C₂H₆) with ethene (C₂H₄).
• Using general formula CₙH₂ₙ for alkanes (correct: CₙH₂ₙ₊₂).
• Saying alkanes decolourise bromine water (that is the alkene test).
• Writing incomplete combustion products as CO₂ only (limited O₂ gives CO or soot).
• Forgetting UV light is needed for halogen substitution with alkanes.

When you need more support

If alkane questions keep costing marks, work through the Alkanes quiz, then get help from a Cambridge IGCSE Coordinated Science tutor.

Frequently asked questions

What is the general formula of alkanes? CₙH₂ₙ₊₂.

Why are alkanes called saturated hydrocarbons? They contain only C and H, with all carbon–carbon bonds as single bonds — no room for more atoms.

What are the products of complete combustion of an alkane? Carbon dioxide and water.

How do I revise alkanes effectively? Learn the first four names and formulas, combustion equations, and why alkanes are unreactive, then take the quiz.

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