Types of Reaction (Edexcel International A Level Chemistry): Revision Note
Types of Reaction
Reactions can be classified as:
Addition
Elimination
Substitution
Oxidation
Reduction
Hydrolysis
Polymerisation
Addition reactions
These involve two reactants combining to form one product
The most common example of an addition reaction involves alkenes, e.g.
C2H4 + H2 → C2H6
C2H4 + Br2 → C2H4Br2
C2H4 + H2O → C2H5OH
Elimination reactions
These are usually identified by one or two reactants forming more products
The products often include an alkene and a smaller molecule that has been eliminated from the reactant, e.g.
CH3CH2Br + OH- C2H4 + H2O + Br–
Substitution reactions
An atom or group of atoms in a compounds is replaced by another atom or group of atoms, e.g.
CH3CH2Br + OH- → C2H5OH + Br–
Oxidation reactions
This can involve the loss of hydrogen or the gain of oxygen
A reactant is oxidised by another chemical species, usually an inorganic reagent, e.g.
CH3CHO + [O] → CH3COOH
In this example, the oxidising agent [O] could be acidified potassium dichromate(VI) solution, Fehling's solution or Tollens' reagent
Reduction reactions
This can involve the gain of hydrogen or the loss of oxygen
A reactant is reduced by another chemical species
This can often be completed using a catalyst and a small reactant molecule such as H2 or HCl, e.g.
CH3CHO + [H] → CH3CH2OH
In this example, the oxidising agent [H] could be lithium aluminium hydride
Hydrolysis reactions
The name can be misleading as hydrolysis suggests that water is being used to split (or lyse) a compound
Hydrolysis reactions are a specific reaction with water, e.g.
CH3Cl + H2O → CH3OH + HCl
Polymerisation reactions
At AS level, you should know about addition polymerisation
This is where the carbon-carbon double bond of an alkene monomer breaks open and forms a polymer chain, e.g.

Addition polymerisation of one alkene monomer is polymerised, a (poly)alkene is formed
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