Chemical reactions that release energy are known as exothermic reactions.

A fuel is a substance that burns to release energy .

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

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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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.

http://www.twigonglow.com/films/glossary/combustion-410/http://www.twigonglow.com/films/oxygen-and-combustion-1449/

air

methane

Water Pump

cobalt chloride paper

Limewater

Carbon dioxide – which turns lime water cloudy

Water – which turns blue cobalt chloride paper to pink

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. 

CH4 + 2O2 CO2 + 2H2O

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.

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.

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

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.

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

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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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.

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.

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

Which of these is a true statement about the changes that occur as hydrocarbon molecules get larger?

A.Boiling point decreases.

B.Viscosity increases.

C.Flammability increases.

D.Transparency increases.

Fuel gas

Petrol / gasoline

Naphtha

Paraffin / Kerosine

Diesel fuel

Fuel and lubricating oil

Bitumen

Burned in the refinery to fuel the distillation process, sold as LPG, purified and sold as bottled camping gas

Fuel for cars and motorcycles, also used to make chemicals.

Used to make chemicals.

Fuel for greenhouse heaters and jet engines, manufacture of chemicals.

Fuel for lorries, trains.

Fuel for the heating systems of large buildings, fuel for ships, lubricating oil.

Roofing, and road surfaces.

Uses of each fraction

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.

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.

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

Using a mnemonic can make learning the names easier. Methane CH4 MonstersEthane C2H6 EatPropane C3H8 PupilsButane C4H10 ButPentane C5H12 PreferHexane C6H14 HairyHeptane C7H16 HaggisOctane C8H18 Occasionally  

Remember that :-

e.g

C3H8 is the molecular formula for propane

and

is the structural formula for propane

               

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

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

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

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

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

Copy and complete the table into your jotter :-

Name Molecular Formula

Full Structural Formula

Ethene C2H4

Propene

Butene

Pentene

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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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.

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

Complete the following word and formula equations.

(i) Octane cracking to give pentane and propene.

(ii) Heptane cracking to produce ethane and pentene.

(iii) Hexane cracking to produce 3 different products.

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Don’t worry about naming the alkenes ,we will return to this later

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.

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.

Can you suggest a way to tell the difference between these two isomers of propene? –

propene C3H6 and cyclopropane C3H6

Straight chain hydrocarbons have all the carbon atoms linked in a continuous chain

H C

H

H

4 C

H

H

3 C

H

H

2 C

H

H

H1

Branched chain hydrocarbons have one or more side chains coming from the main chain

H C

H

H

5 C

H

H

4 C

H

H

3 C

H

H

H1C

H

2

C

H

HH

Naming Branched Alkanes

H C

H

H

8 C

H

H

6 C

H

H

H1C

H

5

C

H

HH

C

H

H

4 C

H

H

3C

H

H

7 C

H

2

C

H

HH

Name the main chain

Name the side group

Number the position of the side group

8 carbon chain so based on octane

two CH3 groups so dimethyl

methyl groups are on carbons 2 and 5

H C

H

H

8 C

H

H

6 C

H

H

H1C

H5

C

H

HH

C

H

H

4 C

H

H

3C

H

H

7 C

H2

C

H

HH

2,5- dimethyloctane

Shortened Structural Formula

H C

H

H

5 C

H

H

4 C

H

H

3 C

H

H

H1C

H

2

C

H

HH

2-methylpentane

2-methylpentane can also be shown by its shortened structural formula

CH3CH2CH2CHCH3

CH3

Naming Alkenes

H C

H

H

8 C

H

H

6 C

H

H

H1C

H

5

C

H

HH

C

H

4 C

H

3C

H

H

7 C

H

2

C

H

HH

Number main chain

Number position of double bond

Name side groups

Number position of side groups

oct-3-ene

dimethyl

2,5-dimethyloct-3-ene

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.

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.

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

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 .