This is a summary of the topic "Alkanes and Alkenes" in the GCE O levels subject: Chemistry. Students taking either the combined science (chemistry/physics) or pure chemistry will find this useful. These slides are prepared according to the learning outcomes required by the examinations board.

3. ORGANIC COMPOUNDS
Most organic compounds contain the element carbon.
Organic compounds that contain only hydrogen and carbon are called hydrocarbons.

4. ORGANIC COMPOUNDS
There are millions of different organic compounds and hence the need to classify them. They are
grouped into families called homologous series.
Examples of homologous series:
• Alkanes
• Alkenes
• Alcohols
• Carboxylic acids

5. ORGANIC COMPOUNDS
A homologous series is a family of organic compounds with the same general formula and
functional group.
A functional group is an atom or group of atoms that gives a molecules its characteristic
properties (the type of reactions it can undergo).

6. ORGANIC COMPOUNDS
Organic compounds in the same homologous series have the following properties:
• Same functional group
• Similar chemical properties
• Gradual change in their physical properties as we go down the series

7. GENERAL FORMULAS AND FUNCTIONAL
GROUPS
Alkanes have a general formula of CnH2n+2 and a carbon-carbon single bond functional group.
Alkenes have a general formula of CnH2n and a carbon-carbon double bond functional group.
Alcohols have a general formula of CnH2n+1OH and a hydroxyl (-OH) functional group.
Carboxylic acids have a general formula of CnH2n+1COOH and a carboxyl (-COOH) functional group.
n refers to the number of carbon atoms in the compound.

8. NAMING ORGANIC COMPOUNDS
Prefix Meth- Eth- Prop- But-
Number of carbon atoms per molecule One Two Three Four
Suffix -ane -ene -ol -oic acid
Homologous series alkane alkene alcohol carboxylic acid

9. NAMING ORGANIC COMPOUNDS
The prefix tells us how many carbon atoms are there in the molecule.
The suffix tells us which homologous series the compound belongs to.
For example, methane can be read into 2 parts: meth-ane
Meth: stands for 1 carbon
ane: stands for alkanes (General formula of CnH2n+2, where n stands for number of carbon)
Hence, Methane is a alkane with 1 carbon atom, and using the general formula, we have CH4.

10. PETROLEUM AND NATURAL GAS
Petroleum is a naturally occurring mixture of hydrocarbons which are mainly alkanes and the
main constituent of natural gas is methane.

11. FRACTIONAL DISTILLATION
Petroleum in its natural state is a dark, smelly liquid that is very viscous. It needs to be separated
into its respective parts before it can be useful.
Petroleum can be separated into useful fractions by fractional distillation.
They are separated according to their boiling points.

12. USES OF PETROLEUM FRACTIONS
Fractions Uses
Petroleum gas Fuel for cooking and heating
Petrol (Gasoline) Fuel for vehicles
Naphtha Feedstock (raw materials) for making petrochemicals such as
plastics and detergents
Kerosene (Paraffin) Fuel for aircraft engines, cooking using oilstoves and heating
Diesel oil Fuel for diesel engines in buses, lorries and trains
Lubricating oil For lubricating machines and for making waxes and polishes
Bitumen For making road surfaces and roofing

13. COMPETING USES OF PETROLEUM
Petroleum is used as fuel to generate heat and electricity as well as a feedstock in manufacturing
plastics, detergents and synthetic rubber.
Supply of petroleum is limited and since both use petroleum for their own purposes, they are
considered to be competing for the same resource.
We need to conserve petroleum to ensure sustainability of this resource.

14. ALTERNATIVE FUELS
Biofuel is a good alternative to petroleum. Biogas are produced when organic matter decays and
biodiesel is made from plants oils like palm oil.

16. ALKANES
Alkanes are a homologous series of hydrocarbons that contain only carbon-carbon single
covalent bonds.
General formula: CnH2n+2
Alkanes are saturated hydrocarbons because they contain only carbon-carbon single covalent
bonds.

17. PHYSICAL PROPERTIES OF ALKANES
Physical properties change down the series:
• Melting and boiling points increase
• Become more viscous
• Less flammable

18. CHEMICAL REACTIONS OF ALKANES
Alkanes are generally unreactive due to the strong bonds within the compound which are difficult
to break. However, alkanes can undergo the following reactions:
• Combustion
• Substitution reactions
• Cracking

19. CHEMICAL REACTIONS OF ALKANES
Combustion:
General equation (complete combustion)
Alkane + oxygen  carbon dioxide + water vapour
Example:
CH4 + 2O2  CO2 + 2H20

20. CHEMICAL REACTIONS OF ALKANES
When there is insufficient supply of air or oxygen, incomplete combustion occurs to give you
carbon, carbon monoxide, carbon dioxide and water vapour.

21. CHEMICAL REACTIONS OF ALKANES
Substitution with chlorine:
Conditions:
Chlorine gas
UV light
/Sunlight
1
2
3
4

22. CRACKING OF PETROLEUM
Cracking is the breaking down of long-chain hydrocarbons into smaller molecules. This is done by
passing the petroleum fraction over a catalyst at a high temperature.

23. CRACKING OF PETROLEUM
long chain alkanes  alkenes + alkanes or hydrogen gas
C6H14  C4H10 + C2H4
Conditions:
High temperature of 6000C
Aluminium oxide Al2O3 and
Silicon dioxide (SiO2) as
catalysts

25. ALKENES
Alkenes are a homologous series of hydrocarbons that contain carbon-carbon double covalent
bonds.
General formula: CnH2n
Alkenes are unsaturated hydrocarbons because they contain carbon-carbon double covalent
bonds.

26. PHYSICAL PROPERTIES OF ALKENES
Physical properties change down the series:
• Melting and boiling points increase
• Become more viscous
• Less flammable

27. CHEMICAL REACTIONS OF ALKENES
Alkenes are unsaturated compounds and generally reactive due to the carbon-carbon double
bonds which will readily undergo addition reactions. Alkene can undergo the following reactions:
• Combustion
• Hydrogenation
• Bromination
• Hydration
• Addition polymerisation

28. CHEMICAL REACTIONS OF ALKENES
Combustion:
General equation (complete combustion)
Alkene + oxygen  carbon dioxide + water vapour
Example:
C2H4 + 3O2  2CO2 + 2H20

29. CHEMICAL REACTIONS OF ALKENES
When there is insufficient supply of air or oxygen, incomplete combustion occurs to give you
carbon, carbon monoxide, carbon dioxide and water vapour.

30. CHEMICAL REACTIONS OF ALKENES
Addition of hydrogen (Hydrogenation):
General equation: Alkenes + hydrogen  alkanes
Example:Ethene + hydrogen  Ethane
Conditions
Hydrogen
2000C
Nickel catalyst

31. CHEMICAL REACTIONS OF ALKENES
Addition of bromine (Bromination):
General equation: Alkene + halogen  (halogen)alkane
Example: Ethene + Bromine  1,2 dibromoethane
Reagent:
Aqueous bromine

32. CHEMICAL REACTIONS OF ALKENES
Addition of steam (Hydration):
General equation: Alkene + steam--> Alcohol
Example: Ethene + steam  ethanol
Reagents:
Steam
3000C
60 atm
Phosphoric(V) acid,
H3PO4

33. CHEMICAL REACTIONS OF ALKENES
Addition polymerisation:
Conditions:
High temperature and pressure
Catalyst

34. CHEMICAL REACTIONS OF ALKENES
From a monomer, the double bonds break and becomes a repeat unit. These repeat units combine to form a
polymer. In the above example, ethene is the monomer which forms the repeat unit which eventually
combines to form poly(ethene), which means “many ethene”.

35. CRACKING OF PETROLEUM
Cracking is the breaking down of long-chain hydrocarbons into smaller molecules. This is done by
passing the petroleum fraction over a catalyst at a high temperature.

36. CRACKING OF PETROLEUM
long chain alkanes  alkenes + alkanes or hydrogen gas
C6H14  C4H10 + C2H4
Conditions:
High temperature of 6000C
Aluminium oxide Al2O3 and
Silicon dioxide (SiO2) as
catalysts

37. IMPORTANCE OF CRACKING
Cracking is used to produce:
• Short chain alkenes
• Hydrogen
• Petrol

38. COMPARING ALKANES AND ALKENES
Property Alkanes Alkenes
Molecular structure Contains only carbon-carbon
single bonds
Saturated compounds
Contains carbon-carbon double
bonds
Unsaturated compounds
Reactivity Generally unreactive Very reactive
Type of reaction Substitution reactions Addition reactions
Reaction with bromine No Rapidly decolourises aqueous
bromine
Undergoes polymerisation? No Yes

40. FATS AND OILS
Polyunsaturated fats or oils contain more than one carbon-carbon double bond. Fats are solids at
room temperature and pressure as they contain mostly saturated fat molecules. Oils are liquids at
room temperature and pressure as they contain mostly unsaturated fat molecules.

41. PRODUCTION OF MARGARINE
We add hydrogen to vegetable oil to produce margarine. This process is hydrogenation, which can
be found at here.

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