Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

2.7.1Unit 2. Energetics, Group Chemistry, Halogenoalkanes and Alcohols

Types of Reaction — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions

5 min read 4 parts Lesson 44 of 53 Unit quiz

📚 IAL Edexcel Linear (Chemistry) Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read

Part 1 of 4Addition, Elimination and Substitution

2.7.1 Types of Reaction

These three types are distinguished by what happens to the number of reactants and products.

Addition
  • Two reactants combine to give one product, as when ethene reacts with bromine: C₂H₄ + Br₂ → C₂H₄Br₂.
Elimination
  • A small molecule such as H₂O or HBr is removed from one reactant, leaving a double bond, as in CH₃CH₂Br → C₂H₄ + HBr.
Substitution
  • One atom or group is replaced by another, as in CH₃CH₂Br + OH⁻ → CH₃CH₂OH + Br⁻.
Addition example
  • Ethene and hydrogen bromide give bromoethaneC₂H₄ + HBr → C₂H₅Br.
Elimination example
  • Ethanol heated with concentrated acid loses water to form ethene.
Counting products
  • A quick check is to count reactants and products: two reactants forming one product suggests an addition reaction.

Part 2 of 4Oxidation, Reduction and Hydrolysis

Oxidation, Reduction and Hydrolysis
Oxidation
  • In organic chemistry oxidation is gain of oxygen or loss of hydrogen, for example CH₃CHO + [O] → CH₃COOH.
Reduction
  • Reduction is loss of oxygen or gain of hydrogen, for example CH₃CHO + 2[H] → CH₃CH₂OH.
Hydrolysis
  • A compound is split by reaction with water, as in CH₃Cl + H₂O → CH₃OH + HCl.
[O] and [H]
  • Square brackets show an oxidising or reducing agent whose exact identity is not given.
Polymer example
  • Poly(ethene) forms when many ethene molecules join, as in n CH₂=CH₂ → (-CH₂-CH₂-)ₙ.

Part 3 of 4Addition Polymerisation

1
Many identical alkene molecules, called monomers, are involved, each with a C=C double bond.
2
The double bond in each monomer opens up and the monomers join end to end.
3
No atoms are lost, so the polymer has the same empirical formula as the monomer.
4
The product is a long saturated chain with repeating units, such as poly(ethene) from ethene.
5
Addition polymerisation is an addition reaction repeated many times.
6
Because no by-product forms, addition polymerisation has an atom economy of 100%.

Part 4 of 4Exam Checklist & Tips

2.7.1 – Key Points for the Exam

  • Addition A reaction in which two molecules combine to form a single product.
  • Elimination A reaction in which a small molecule is removed from a larger one, leaving a double bond.
  • Substitution A reaction in which an atom or group is replaced by another.
  • Hydrolysis A reaction with water that breaks a bond in a compound.
  • Monomer A small molecule that can join with others to form a polymer.

Common Mistakes

  • Calling the reaction of ethene with bromine substitution because bromine is added; it is addition.
  • Mixing up elimination, which loses a small molecule, with substitution, which swaps groups.
  • Forgetting that hydrolysis is a reaction with water, not any reaction in solution.
  • Describing polymerisation as losing small molecules, which is true for condensation but not for addition polymerisation.

Last updated:

\n