Fossil Fuels

Fossil fuels are finite resources because they are no longer being made, or are being made extremely slowly.

Fossil fuels are being used up faster than they are being formed. They are called non-nenewable resource.

Specific difficulties associated with the finite nature of crude oil include;

all the readily extractable resources will be used up in the future

finding replacements.

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Fractional distillation

Crude oil is a mixture of many types of oil, which are all ;hydrocarbons', a hydrocarbon is made up of molecules containing carbon and hydrogen only.

Crude oil is heated at the bottom of a fractionating column, Oil that doesnt boil sinks to the bottom as a thick liquid. This is bitumen. Bitumen has a very high boiling point, it exits at the bottom of the column

 Other fractions, containing mixtures of hydrocarbons with similar boiling points, boil and their gases rise up the column, the column is cooler at the top, fractions with lower boiling points exit towards the top of the column.

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more on fractional distillation

Crude oil can be seperated because the hydrocarbons in different fractions have differently sized molecules.

The forces between the molecules are intermolecular forces and are broken during boiling.

The molecules of the liquid seperate from each other as molecules of gas.

Large molecules, such as those of bitumen and heavy oil, have strong forces of attraction. A lot of energy is needed to break the forces between the molecules. These fractions have high boiling points.

Smaller molecules, such as petrol, hace weak attractive forces between them and are easily seperate. Less energy is needed to break the forces between the molecules. These fractions have low boiling points.

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Problens in extracting crude oil

Transporting oil can cause problems. Oil slicks can damage birds feathers and cause their deaths. Clean-up operations use detergents that can damage wildlife.

There may be political problems related to the extraction of crude oil, particulary where the uk is dependent on oil and gas from politically unstable countries.

 Oil-producing nations can set high prices and cause problems for the future supply of non oil producing nations.

Because the demand for oil and its products is very high, there is conflict between the needs for making petrochemicals and for making fuels. A fraction called naphtha is in high demand for use in medicines, plastics and dyes.

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Cracking is a process that turns large alkane molecules into smaller alkene molecules.

An alkene molecule has a double bond, which makes it useful for making polymers.

Cracking also helps oil manufacturers match supply with demand for products like petrol.

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choosing fuels

A fuel is chosen of its key features, for example coal produces more pollution than petrol.

The amount of fossil fuels being burnt is increasing because populations are increasing.

Goverments are concerned because of the increasing carbon dioxide emissions that result when fossil fuels are burned.

Countries with huge populations such as india or china, are now using more fuel which adds further to gas emissions.

Many goverments have pledged to try and cut carbon dioxide emissions over the next 15-20 years. It is a global problem that cannot be solved by one country alone.

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Burning hydrocarbon fuels in plenty of air produces carbon dioxide and water.

methane+oxygen=carbon dioxide+water

Complete combustion occurs when a fuel burns plenty of oxygen. More energy is released during complete combustion than during incomplete combustion,

Toxic gas (carbon monoxide) and soot (carbon) is made during incomplete combustion;

fuel+oxygen=carbon monoxide+water  OR  fuel+oxygen=carbon+water

Given the molecular formula of a hydrocarbon, balanced symbol equations can be constructed for;

complete combustion(                        )  incomplete combustion (                             )

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Clean air

Clean air is made up of 78% nitrogen, 21% oxygen and of the remaining 1% only 0.035% is carbon dioxide.

These percentages change very little because there is a balance between the processes that use up and make both carbon dioxide and oxygen.

Some of these processes are shown in the carbon cycle. ( see carbon cycle pg 6 of revision guide)

Over the last few centuries the percentage of carbon dioxide in air has increased slightly due to a number of factors including;

deforestation- as more rainforests are cut down less photosynthesis takes place

increased population- as populations increase, the worlds energy requirements increase.  

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The atmosphere

Gases escaping from the interior of the earth formed the original atmosphere. Plants that could photosynthesise removed carbon dioxide from the atmosphere and added oxygen. Eventually this amount of oxygen reached its current level,

Gases come from the centre of the earth through volcanoes in a process called degassing. Scientists analyse the composition of these gases to form theories about the original atmosphere.

One theory is that the atmosphere was originally rich in water vapour and carbon dioxide. This vapour condensed to form oceans and the carbon dioxide dissolved in the water. The percentage of nitrogen slowly increased and, being unreactive, little nitrogen was removed.

Over time, organisms that could photosynthesiseevolved and converted carbon dioxide snd water into oxygen. As the percentage of oxygen in the atmosphere increased, the percentage of carbon dioxide decreased, until todays levels were reached.

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Pollution control

It is important to control atmospheric pollution because of the effects it can have on peoples health, the natural enviroment and the built enviroment.

Sulfur dioxide is a pollutant that can cause difficulties for people with asthma. It can also dissolve in water to form acid rain that damages wildlife and limestone buildings.

A car fitted with a catalytic converter changes carbon monoxide into carbon dioxide.

In a catalytic converter a reaction between nitric oxide and carbon monoxide takes place on the surface of the catalyst. The two gases formed are natural components of air- nitrogen and carbon dioxide.

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A hydrocarbon is a compund of carbon and hydrogen atoms only.

Alkanes are hydrocarbons that have single covalent bonds only,

 Alkenes are hydrocarbons that have a double covalent bond between carbon atoms. Double bonds involve two shared pairs of electrons.

Propane (       ) is a hydrocarbon because it has only C and H atoms, it is an alkane because all the bonds are single covalent bonds.

Propanol (             ) is not a hydrocarbon because it contains an oxygen atom.

Propene (              ) is a hydrocarbon because it contains only C and H atoms. It is an alkene because it has a double covalent bond between carbon atoms. Propene is also a monomer. Poly(propene) is the polymer.

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more on hydrocarbons

Bromine is used to test for an alkene. When orange bromine water is added to an alkene it turns colourless.

The bromine and alkene form a new compound by an addition reaction. A dibromo compound forms which is colourless.

A saturated compound only has single covalent bonds between carbon atoms. Alkanes, like propane, are saturated. They have no double bond between carbon atoms.

An unsaturated compound has atleast one double covalent bond between carbon atoms. Alkenes, like propene, are unsaturated. They have a C=C double bond.

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Addition polymerisation is the process in which many alkene monomers react to give a polymer. This reaction needs high pressure and a catalyst.

You can recognise a polymer from its displayed formula by looking out for the following; a long chain, the pattern repeating every two carbon atoms, two brackets on the end with extended bonds through them, an 'n' after the brackets.

The displayed formula of; an addition polymer can be constructed when the displayed formula of its monomer is given, a monomer can be constructed when the displayed formula of its addition polymer is given.

During an addition polymerisation reaction a long chain is made until it is stopped. This long molecule is poly(ethene). The reaction causes the double bond in the monomer to break and each of the two carbon atoms forms a new bond.

Addition polymerisation involves the reaction of many unsaturated monomer molecules (alkenes) to form a saturated polymer.

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