Alkanes & Alkenes — GCSE Chemistry Revision
Revise Alkanes & Alkenes for GCSE Chemistry. Step-by-step explanation, worked examples, common mistakes and exam-style practice aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP.
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Go to AlcoholsWhat is Alkanes & Alkenes?
Alkanes and alkenes are two important homologous series of hydrocarbons. Alkanes are saturated, meaning they only have single C-C bonds, and are generally unreactive. Alkenes are unsaturated, containing at least one C=C double bond, which makes them more reactive than alkanes. They undergo addition reactions.
Board notes: The chemistry of alkanes and alkenes is a major part of the organic chemistry section for all boards. You must know their structures, general formulas, and characteristic reactions, including the bromine water test. Cracking is also a key industrial process to understand.
Step-by-step explanationWorked example
Ethene (an alkene, C₂H₄) reacts with bromine (Br₂) in an addition reaction. The C=C double bond breaks, and a bromine atom adds to each carbon atom, forming dibromoethane (C₂H₄Br₂). The orange bromine water is decolourised.
Mini lesson for Alkanes & Alkenes
1. Understand the core idea
Alkanes and alkenes are two important homologous series of hydrocarbons. Alkanes are saturated, meaning they only have single C-C bonds, and are generally unreactive.
Can you explain Alkanes & Alkenes without copying the notes?
2. Turn it into marks
Ethene (an alkene, C₂H₄) reacts with bromine (Br₂) in an addition reaction. The C=C double bond breaks, and a bromine atom adds to each carbon atom, forming dibromoethane (C₂H₄Br₂).
Underline the method, evidence, or command-word move that would earn credit in GCSE Organic Chemistry.
3. Fix the likely mark leak
Watch for this mistake: Confusing the reactions of alkanes and alkenes. Alkanes undergo combustion and substitution reactions (e.g., with halogens in UV light), while alkenes undergo addition reactions at the double bond.
Write one correction rule before doing another practice question.
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Alkanes & Alkenes practice questions
These are original StudyVector questions for revision practice. They are not official exam-board questions.
Question 1
In one GCSE sentence, explain what Alkanes & Alkenes is testing.
Answer: Alkanes and alkenes are two important homologous series of hydrocarbons. Alkanes are saturated, meaning they only have single C-C bonds, and are generally unreactive.
Mark focus: Precise definition and topic focus.
Question 2
A Alkanes & Alkenes question uses an unfamiliar context. What should the answer do before adding detail?
Answer: It should name the process, variable, equation, particle model, or evidence being tested, then explain the result using precise scientific vocabulary.
Mark focus: Method selection and command-word control.
Question 3
A student makes this mistake: "Confusing the reactions of alkanes and alkenes. Alkanes undergo combustion and substitution reactions (e.g., with halogens in UV light), while alkenes undergo addition reactions at the double bond." What should their next repair task be?
Answer: Do one Alkanes & Alkenes question and review the mistake type.
Mark focus: Error correction and next-step practice.
Alkanes & Alkenes flashcards
Core idea
What is the main idea in Alkanes & Alkenes?
Alkanes and alkenes are two important homologous series of hydrocarbons. Alkanes are saturated, meaning they only have single C-C bonds, and are generally unreactive.
Common mistake
What mistake should you avoid in Alkanes & Alkenes?
Confusing the reactions of alkanes and alkenes. Alkanes undergo combustion and substitution reactions (e.
Practice
What is one useful practice task for Alkanes & Alkenes?
Answer one Alkanes & Alkenes question and review the mistake type.
Exam board
How should you use board notes for Alkanes & Alkenes?
The chemistry of alkanes and alkenes is a major part of the organic chemistry section for all boards. You must know their structures, general formulas, and characteristic reactions, including the bromine water test.
Common mistakes
- 1Confusing the reactions of alkanes and alkenes. Alkanes undergo combustion and substitution reactions (e.g., with halogens in UV light), while alkenes undergo addition reactions at the double bond.
- 2Forgetting the test to distinguish between an alkane and an alkene. Alkenes will decolourise bromine water (turn it from orange to colourless), while alkanes will not.
- 3Drawing the structure of an alkene with the wrong number of hydrogen atoms. Remember that each carbon atom can only form a total of four bonds.
Alkanes & Alkenes exam questions
Exam-style questions for Alkanes & Alkenes with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP specifications.
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Step-by-step method
Step-by-step explanation
4 steps · Worked method for Alkanes & Alkenes
Core concept
Alkanes and alkenes are two important homologous series of hydrocarbons. Alkanes are saturated, meaning they only have single C-C bonds, and are generally unreactive. Alkenes are unsaturated, containi…
Frequently asked questions
What is cracking?
Cracking is the process of breaking down large, less useful hydrocarbon molecules (long-chain alkanes) into smaller, more useful ones, including alkanes and alkenes. This is done using high temperatures and a catalyst.
Are alkanes or alkenes more useful?
Both are useful. Alkanes are excellent fuels. Alkenes are more reactive and are used to make polymers (plastics) and other important organic chemicals.