Who this is for: Cambridge IGCSE Chemistry (0620) students who want alkanes — saturated hydrocarbons, combustion and substitution — to become reliable equation answers instead of generic “hydrocarbon” statements.
What query it owns: how to understand and revise alkanes in Cambridge IGCSE Chemistry.
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 with only C–C and C–H single bonds. Cambridge IGCSE Chemistry (0620) tests the general formula (CₙH₂ₙ₊₂), complete and incomplete combustion, and substitution reactions with chlorine in sunlight. Because alkanes are relatively unreactive, examiners often contrast them with alkenes. This guide covers the key reactions, conditions and past-paper wording.

Key takeaways

• Alkanes have general formula CₙH₂ₙ₊₂ — methane (CH₄), ethane (C₂H₆), propane (C₃H₈).
• Complete combustion: alkane + O₂ → CO₂ + H₂O (plenty of oxygen).
• Incomplete combustion: limited O₂ → CO and/or C (soot) + H₂O.
• Substitution with chlorine: alkane + Cl₂ → chloroalkane + HCl, needs UV light or sunlight.
• Alkanes do not decolourise bromine water — that test is for alkenes.

What are alkanes in Cambridge IGCSE Chemistry?

Alkanes form a homologous series of saturated hydrocarbons. They are the main components of fuels such as petrol and natural gas (methane). The syllabus requires balanced combustion equations, an understanding of substitution conditions, and the ability to distinguish alkanes from alkenes using the bromine water test.

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

The core ideas you must master

Feature / reaction	Alkane detail	Conditions / products
General formula	CₙH₂ₙ₊₂	Methane CH₄, ethane C₂H₆
Complete combustion	CH₄ + 2O₂ → CO₂ + 2H₂O	Excess oxygen, heat
Incomplete combustion	2CH₄ + 3O₂ → 2CO + 4H₂O	Limited oxygen
Substitution with Cl₂	CH₄ + Cl₂ → CH₃Cl + HCl	UV light / sunlight
Bromine water test	No change (stays orange)	Distinguishes from alkenes
Source	Petroleum fractions, natural gas	Fuels

Complete vs incomplete combustion

Type	Oxygen supply	Carbon products	Example (methane)
Complete	Excess	CO₂ only	CH₄ + 2O₂ → CO₂ + 2H₂O
Incomplete	Limited	CO and/or C (soot)	2CH₄ + 3O₂ → 2CO + 4H₂O

Alkanes in past-paper wording: command words that matter

Command word	What the question wants	Typical alkanes stem
Write	Balanced equation	”Write an equation for the complete combustion of propane.”
State	Condition or product	”State the condition needed for chlorination of methane.”
Describe	Substitution process	”Describe the reaction between ethane and chlorine.”
Explain	Why alkanes are unreactive	”Explain why alkanes do not decolourise bromine water.”
Name	Product of substitution	”Name the product when methane reacts with chlorine.”

Worked exam-style stems (how to answer the wording)

1. “Write an equation for the complete combustion of ethane.” 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O. Reward: balanced equation with CO₂ and H₂O only.
2. “Describe the reaction between methane and chlorine.” Methane reacts with chlorine in sunlight or UV light in a substitution reaction to form chloromethane and hydrogen chloride. Reward: substitution named + UV/sunlight + products.
3. “Explain why alkanes are described as saturated.” They contain only single C–C bonds — no C=C double bonds; each carbon is bonded to the maximum number of atoms. Reward: single bonds only + no double bonds.

Test yourself with the Alkanes quiz once you have worked through a few examples.

How alkanes connect to the rest of Organic Chemistry

Alkanes link to Fuels (petroleum fractions), Alkenes (contrast reactivity) and Formulae, Functional Groups and Terminology. The Cambridge IGCSE Chemistry resource hub links all units.

Common mistakes students make

• Writing addition instead of substitution for alkane + chlorine reactions.
• Forgetting UV light or sunlight as the condition for chlorination.
• Saying alkanes decolourise bromine water — they do not.
• Balancing combustion equations incorrectly (check O₂ last).
• Confusing incomplete combustion products (CO vs CO₂).

When you need more support

If combustion balancing and substitution conditions keep costing marks, work through the Alkanes quiz to find the gap, then get focused help from a Cambridge IGCSE Chemistry tutor.

Frequently asked questions

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

What condition is needed for the reaction between an alkane and chlorine? UV light or sunlight — without it the reaction is extremely slow.

Do alkanes decolourise bromine water? No — bromine water stays orange; only alkenes decolourise it.

How do I revise alkanes effectively? Learn combustion and substitution with conditions, contrast with alkenes, then take the Alkanes quiz.

Ready to master Cambridge IGCSE Chemistry alkanes?

Start with the Alkanes subtopic page, then book a free trial with a Cambridge IGCSE Chemistry specialist.

Ready to Excel in Your Studies?

Get personalised help from Tutopiya's expert tutors. Whether it's IGCSE, IB, A-Levels, or any other curriculum — we match you with the perfect tutor and your first session is free.

Book Your Free Trial