1. Hydrocarbons and Fuels

2. A fuel is a substance that burns to release energy .
Chemical reactions that release energy are known as exothermic reactions.

3. Fire can be explained using a fire triangle.
The triangle has three sides: fuel, oxygen and heat.
Each of these sides represents a key element for fire to occur. If one of them was removed, the triangle would collapse and the fire would go out

4. Fossil fuels
Fossil fuels were formed over millions of years from the decaying remains of once living things
Fossil fuels are finite resources
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5. Crude oil is a thick black liquid which is made up of a mixture of substances called hydrocarbons
Hydrocarbons are compounds which are made up of the elements carbon and hydrogen only.
Hydrocarbon fuels burn (combust) when they react with oxygen in the air producing the same two products.

6. Water Pump
air
Lime
water
methane
cobalt chloride paper

7. Carbon dioxide – which turns lime water cloudy
Water – which turns blue cobalt chloride paper to pink

8. Copy and complete this paragraph in your jotter :-
The two products of combustion are _________ and __________ ___________. All hydrocarbons burn to produce these products.
methane oxygen - _________ _______
Now change this word equation into a formula equation and balance it.

9. CH4 + 2O2  CO2 + 2H2O

10. If there is insufficient air for complete combustion, incomplete combustion takes place.
Hydrogen is still oxidised to water, but carbon monoxide forms instead of carbon dioxide.
Carbon monoxide is a toxic gas, so adequate ventilation is important when burning fuels.

11. Several waste products are also released when fuels burn
Several waste products are also released when fuels burn. These do not just disappear and they can harm the environment by contributing to global warming and acid rain.
Carbon dioxide dissolves in water in the atmosphere to form a weakly acidic solution. This means that rainwater is naturally slightly acidic. However, some of the products from burning fuels make rainwater more acidic than normal. This is acid rain.

12. Most hydrocarbon fuels naturally contain some sulphur compounds.
When the fuel burns, the sulphur it contains is oxidised to sulphur dioxide:
sulphur + oxygen → sulphur dioxide
This gas dissolves in water to form an acidic solution. It is a cause of acid rain

13. Acid rain reacts with metals and rocks such as limestone, causing damage to buildings and statues.
Acid rain damages the waxy layer on the leaves of trees. This makes it more difficult for trees to absorb the minerals they need for healthy growth and they may die.
Acid rain also makes rivers and lakes too acidic for some aquatic life to survive.

14. If the video does not start from the slide there is a copy of the video on the server .

15. The hydrocarbon fractions in crude oil need to be separated out to make them useful.
This is done using a special type of distillation called Fractional Distillation.
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16. The smallest hydrocarbons (which have the lowest boiling points) boil first.
These vapours go straight to the top of the tower and are collected first.
As the size of the hydrocarbons increase, the boiling points increase, and these hydrocarbons are collected further down the column.
Eventually, the last fraction consists of a very thick, black substance.

18. Flammability is how easy it is for something to burn
Viscosity is how thick something is.
Ease of Evaporation is how easily it is for something to turn into a gas.

19. Copy and complete the following table to show how the properties of different fractions change with molecular size

20. Which of these is a true statement about the changes that occur as hydrocarbon molecules get larger?
Boiling point decreases.
Viscosity increases.
Flammability increases.
Transparency increases.

21. Uses of each fraction
Burned in the refinery to fuel the distillation process, sold as LPG, purified and sold as bottled camping gas
Fuel gas
Petrol
/ gasoline
Fuel for cars and motorcycles, also used to make chemicals.
Naphtha
Used to make chemicals.
Paraffin /
Kerosine
Fuel for greenhouse heaters and jet engines, manufacture of chemicals.
Diesel fuel
Fuel for lorries, trains.
Fuel and
lubricating
oil
Fuel for the heating systems of large buildings, fuel for ships, lubricating oil.
Bitumen
Roofing, and road surfaces.

22. Alkanes

23. The alkanes are a family of hydrocarbons that share the same general formula.
This is:
CnH2n+2
The general formula means that the number of hydrogen atoms in an alkane is double the number of carbon atoms, plus two.
The alkanes form part of what is known as a homologous series.
A homologous series is a series of compounds that have similar
properties and the same general formula.

24. Alkanes are saturated hydrocarbons.
This means that their carbon atoms are joined to each other by single bonds.
This makes them relatively unreactive, apart from burning or combustion, which is their reaction with oxygen in the air.

25. There are many members of the alkanes, but for the purposes of this course, we only need to know the first 8 members. These are: -
Methane - CH4
Ethane - C2H6
Propane - C3H8
Butane - C4H10
Pentane - C5H12
Hexane - C6H14
Heptane - C7H16
Octane - C8H18

26. Using a mnemonic can make learning the names easier.
Methane CH4 Monsters
Ethane C2H6 Eat
Propane C3H8 Pupils
Butane C4H10 But
Pentane C5H12 Prefer
Hexane C6H14 Hairy
Heptane C7H16 Haggis
Octane C8H18 Occasionally

27. Remember that :-
e.g
C3H8 is the molecular formula for propane
and
is the structural formula for propane

28. The structural formula is shown as a 2D representation but remember that you can draw a 3D representation using a flying wedge projection
e.g. methane can be shown in 2D as
And can be shown on 3D as
This allows the tetrahedral arrangement to be seen more clearly

29. Isomers

30. Isomers are molecules with the same chemical formula but different structural formula.
This means that they contain the same atoms but how the atoms are
joined together is different. Making them different compounds

31. View video
Don’t worry about naming the alkanes . We will return to this later .

32. Alkenes

33. The second homologous series is the alkenes
The second homologous series is the alkenes. Their names all end in –ene for example ethene.

34. The alkenes all contain a double bond
For this reason, alkenes all have 2 less hydrogens than the corresponding alkane
Methene does not exist since a molecule must have at least 2 carbon atoms to have a double bond.
The general formula for the alkenes is CnH2n

35. Full Structural Formula
Copy and complete the table into your jotter :-
Name
Molecular Formula
Full Structural Formula
Ethene
C2H4
Propene
Butene
Pentene

36. Alkenes are said to be unsaturated hydrocarbons because of the double bond between two carbon atoms in the molecule.
Alkanes and alkenes are very alike. What is needed is a chemical test that will tell you which is which.
Alkenes will decolourise bromine solution.
Alkanes will not
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37. Crude oil often contains too many large hydrocarbon molecules and not enough small hydrocarbon molecules. There is more demand for shorter alkane molecules and alkenes than for the many of the longer chains formed during fractional distillation. This is where cracking comes in.
Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful hydrocarbon molecules.

38. Cracking produces a mixture of smaller alkanes and alkenes
Cracking produces a mixture of smaller alkanes and alkenes. This helps to meet the demand for the more useful
smaller fractions and to increase profit.
Now watch the animation showing the cracking of large hydrocarbons (BBC Bitesize).
ANIMATION

39. Complete the following word and formula equations.
Octane cracking to give pentane and propene.
Heptane cracking to produce ethane and pentene.
(iii) Hexane cracking to produce 3 different products.

40. Alkene isomers
Alkene isomers

41. View video
Don’t worry about naming the alkenes ,we will return to this later

42. Cycloalkanes
Cycloalkanes

43. Cycloalkanes
Another way of putting carbon and hydrogen together is in rings
This family is called the cycloalkanes
These compounds are isomers of the alkenes i.e they have the same molecular formula (CnH2n) but the atoms are joined together differently.

44. Cycloalkanes only contain carbon-hydrogen bonds and carbon-carbon single bonds, but this time the carbon atoms are joined up in a ring.
The smallest cycloalkane is cyclopropane.

45. Can you suggest a way to tell the difference between these two isomers of propene? –
propene C3H and cyclopropane C3H6

46. Naming branched alkanes

47. Straight chain hydrocarbons have all the carbon atoms linked in a continuous chain4 3 2 1

48. Branched chain hydrocarbons have one or more side chains coming from the main chain5 4 3 1 2

49. Naming Branched Alkanes8 6 1 5 4 3 7 2
8 carbon chain so based on octane
Name the main chain
two CH3 groups so dimethyl
Name the side group
Number the position of the side group
methyl groups are on carbons 2 and 5

50. H C 8 6 1 5 4 3 7 2
2,5- dimethyloctane

51. Shortened Structural Formula5 4 3 1 2
2-methylpentane

52. 2-methylpentane can also be shown by its shortened structural formula
CH3CH2CH2CHCH3
CH3

53. Naming Alkenes H C Number main chain oct-3-ene8 6 1 5 4 3 7 2
Number main chain
oct-3-ene
Number position of double bond
dimethyl
Name side groups
Number position of side groups
2,5-dimethyloct-3-ene

61. Renewable Fuel - Biomass

62. A renewable form of energy - BIOMASS
Have you ever sat by a campfire or fireplace?
If so, you've seen biomass energy in action. Biomass is any natural matter like trees, plants, or animal waste that can be used as an energy source.
Energy comes from the sun through a process called photosynthesis, and is released when biomass is burned or decomposes.
It can be used as a source of biofuels (a renewable energy source), to reduce our dependence on fossil fuels and to help reduce air pollution.

63. Burning biomass releases carbon dioxide.
Having too much carbon dioxide in the atmosphere is contributing to the greenhouse effect.
However the plants that produce biomass also use carbon dioxide to grow their leaves flowers, branches, and stems.
The use of biomass for energy production is said to be carbon neutral.

64. The vital difference between biomass and fossil fuels is one of time scale.
Biomass takes carbon out of the atmosphere while it is growing, and returns it as it is burned.  If it is managed on a sustainable basis, biomass is harvested as part of a constantly replenished crop. This maintains a closed carbon cycle with no net increase in atmospheric carbon dioxide levels.
Fossil fuels such as coal, oil and gas are also derived from biological material, however material that absorbed carbon dioxide from the atmosphere many millions of years ago . Burning fossil fuels therefore adds carbon dioxide to the atmosphere

65. Examples of Biomass:-
Biogas - produced when bacteria break down sewage in a digester .
The methane gas produced by the bacteria can be used as a fuel.
Bioethanol – yeast breaks down sugar in sugar cane to produce alcohol.
Bioethanol is used in Brazil to fuel cars
Fast growing timber- fast growing trees such as willow can be burned in power stations. Electricity is generated using renewable biomass instead of fossil fuels .