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4dOrganic Chemistry

Alkenes — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions

5 min read 7 parts Lesson 4 of 18 1 quiz

📚 Edexcel Linear - OL (Chemistry) Hub / Topical Revision
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Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
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Lesson summary

Alkenes Edexcel O Level Linear Chemistry notes: know that alkenes contain the functional group >C=C<Alkenes are made by cracking long-chain alkanes.First three alkenesethene, propene, butene.know that alkenes contain the functional group >C=C<know the general formula for alkenese…

  • Alkenes Edexcel O Level Linear Chemistry: what to do next
  • Unsaturated
  • Addition reaction
  • Bromine water test
  • Hydrogenation
  • Give / State / Name

Part 1 of 6Key ideas

1
Alkenes are made by cracking long-chain alkanes.
2First three alkenes
First three alkenes ethene, propene, butene.

Part 2 of 6Syllabus points

1
know that alkenes contain the functional group >C=C<
2
know the general formula for alkenes
3
explain why alkenes are classified as unsaturated hydrocarbons
4
understand how to draw the structural and displayed formulae for alkenes with up to four carbon atoms in the molecule, and name the unbranched-chain isomers knowledge of cis/trans or E/Z notation is not required
5
describe the reactions of alkenes with bromine to produce dibromoalkanes
6
describe how bromine water can be used to distinguish between an alkane and an alkene

Part 3 of 6Process & sequence

  • Alkane (long chain)
  • Cracking
  • Shorter alkane + alkene
  • Addition reactions
Alkanes vs alkenes
Alkanessaturated, bromine stays orange
Alkenesunsaturated, decolourise bromine water
Alkenes more reactive

Part 4 of 6Summary

Summary
Alkenes decolourise bromine water.
The general formula of alkenes is CnH2n.

Part 5 of 6Keep going

Alkenes Edexcel O Level Linear Chemistry: what to do next

These Alkenes Edexcel O Level Linear Chemistry notes covered the key ideas, worked examples and exam technique for this topic. Check your Alkenes Edexcel O Level Linear Chemistry understanding with the practice questions below, then reread any Alkenes Edexcel O Level Linear Chemistry point you were unsure about before moving on.

1
Practice: Alkenes Edexcel O Level Linear Chemistry practice questions
2
Previous lesson: 4c Alkanes — Notes
3
Next lesson: 4h Synthetic polymers — Notes
4
Course: Edexcel Linear – OL (chemistry) — all units
5
Official syllabus: Pearson Edexcel International GCSEs

Alkenes Edexcel O Level Linear Chemistry revision notes

Part 6 of 6Compare: Compare

Addition reactions of ethene
ReagentConditionsProductTypeUseEquation
BromineRoom temperature1,2-dibromoethaneAdditionTest for C=CC₂H₄ + Br₂ → C₂H₄Br₂
HydrogenNi catalyst, 150 °CEthaneHydrogenationMargarineC₂H₄ + H₂ → C₂H₆
SteamH₃PO₄, 300 °C, 60 atmEthanolHydrationIndustrial ethanolC₂H₄ + H₂O → C₂H₅OH
Ethene (many)High pressure, catalystPoly(ethene)Addition polymerisationPlastic bagsn C₂H₄ → (C₂H₄)n

Key terms

Command terms

Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.

Exam technique

Keywords the mark scheme looks for in this lesson

Keywords the mark scheme looks for in this lesson
Alkene · Unsaturated · Addition reaction · Bromine water test · Hydrogenation · Hydration
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. electronegativity, nucleophile, dynamic equilibrium, activation energy).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.

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