Core Chemistry - Topic 5 Fuels

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  • Created by: Katie
  • Created on: 15-04-13 21:01

Crude Oil

  • Crude oil and natural gas - FOSSIL FUELS
  • Crude oil - a thick black liquid found in some sedimentary rocks
    • useful products obtained e.g. petrol, diesel
  • Found deep underground (with natural gas)
    • been trapped by layers of rock preventing the liquid and gas from rising
  • Formed over millions of years 
    • remains of microscopic plants and animals that lived in the sea
    • fell to the sea bed when dead and were buried by sediments
    • sediments kept oxygen away and prevented decay
    • heat and pressure increased as layers grew
    • turned into oil or gas(
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Crude Oil Fractions

  • Fractional distillation - process used to serarate mixtures of different liquids
  • Crude oil hydrocarbons are not easy to use when mixed together
    • sent to oil refinery to be separated into simpler mixtures
  • Mixture of liquids is boiled and the vapour is condensed
    • these simpler mixtures are called fractions
    • the different fractions condense at different temperatures
  • Each fraction is still a mixture of different hydrocarbon molecules
    • but they contains a group of hydrocarbons more limited in, range of numbers of carbon atoms, in a molecule.
    • e.g. the petrol fractions has 5, 6 or 7 carbon atoms per molecule
  • The percentage of each factions varies depending on where in the world it was obtained
    • so some crude oils are more valuble than others
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Crude Oil Fractions Continued

  • Each fraction has different uses based on different properties
    • gases - fuel for vehicles, bottled for camping stoves, heating and cooking in homes
    • petrol - fuel for cars
    • kerosene - fuel for aircraft engines
    • diesel oil - fuel for diesel engines (some cars, lorries, trains)
    • fuel oil - fuel for large ships, some power stations, heating, lubricating oil
    • bitumen - making roads, waterproofing flat roofs
  • Gases / petrol / kerosene
    • short carbon chains (few carbon atoms)
    • low boiling points
    • ignite easily
    • runny viscosity
  • Diesel oil / fuel oil / bitumen
    • long carbon chains (up to 40 carbon atoms)
    • hight boiling points
    • difficult to ignite
    • thick and sticky viscosity
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  • Combustion - an oxidation reaction of the burning of fossil fuels
    • reacting with oxygen releasing heat and light energy
  • All hyrdrocarbon fuels produce carbon dioxide and water when they burn
    • as long as there is enough oxygen present
  • Methane is the main gas in natural gas
  • Complete combustion - if all of the hydrocarbon is used up during combustion and the only products are carbon dioxide and water
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Incomplete Combustion

  • Incomplete combustion - occurs when the burning fuel doesn't have enough oxygen for all of the carbon atoms to form carbon dioxide
  • Some carbon atoms form carbon monoxide and some form solid carbon particles (soot)
  • Different amounts are produced depending on the amount of oxygen available
  • Carbon monoxide - odourless and colourless toxic gas
  • Carbon monoxide atoms are similar in stucture to oxygen atoms and can imitate them in your red blood cells
    • this causes your body to be starved of oxygen and sufficates you
  • 40 people die per year of carbon monoxide poisioning
    • faulty gas boilers or fires
    • also produced by car engines
  • Soot can clog up pipes that send waste gases away
    • can also cause fires in chimneys if it builds up
  • Produced by vehiciles (especially diesel)
  • Can collect in the lungs if sooty air is breathed in causing lung disease
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Acid Rain

  • 1970 - acid lakes, death of fish, damaged trees
  • Winds blowing pollution from factories and power stations
    • carried in the atmosphere making rainfall acidic
    • damaged trees and killed fish
  • Acid rain - rain that's more acidic than normal - pH <5.2
  • Effects include:
    • acidic rivers, lakes and soil - harming organisms
    • damaging trees
    • weathering of limestone or marble buildings
    • corrosion of metal
  • Solutuons include:
    • reduce amount of sulfur in petrol, diesel and fuel oil
    • removing acidic gases from power station emissions
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Climate Change

  • Surface temperature on Earth varies
    • between the Equator and the poles
    • changing seasons and weather patterns
    • over hundreds of years
  • Current average Earth temperature - 14 degrees C
  • Carbon dioxide, methane and warer vapour in the atmosphere trap heat energy
    • without the gases average Earth temperature - -18 degrees C
  • Carbon dioxide concentration can change due natural processes e.g. volcaonoes
  • Increase is due to human activities e.g. burning fossil fuels and farming
  • Most scientists and governments believe this to be the case
  • Likely to cause change in global weather patterns and climate
  • Reduce amount of carbon dioxide by reducing burning fossil fuels
    • iron compounds added to oceans IRON SEEDING - encourage microscopic plants to grow - removing carbon dioxide through photosynthesis - die and sink to ocean floor - carbonate shells buried for long time
    • catch carbon dioxide from fossil fuel power stations - react to make hydrocarbon compounds - use as fuels
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  • Biofuels - obtained from living organisms or organisms recently died
    • wood and dried animal droppings used for years
    • waste materials like wheats stalks, peanut shells, branches burnt in power stations
  • Ethanol - processing wheat, sugar cane or sugar beet
    • mixed with petrol for car engines
    • reduces petrol demand and conserves crude oil suplies
  • Biodiesel - fuel made of vegetable oils by chemical reactions
    • produced from oil seedrape, soya beans or used cooking oil from restaurants
    • diesel engines can run on biodiesel or a mixture with normal diesel
  • Biofuel could replace most of the fossil fuel we use
  • Renewable resourse
  • Carbon neutral (only putting back carbon dioxide that photosynthesis takes out)
  • Energy needed to make -  fertilisers for crops, harvesting crops, process into biofuels, transport, etc
  • Energy for these processe will come from fossil fuels!
  • Lots of crops would need to be grown - less for food
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Choosing Fuels

  • Hydrogen and oxygen can react and release energy without burning
    • this happens in a fuel cell
    • water is the only waste product
    • often called a 'clean' fuel
  • Most fuels we use cause some pollution
    • some produce sulfur which forms sulfur dioxide when it burns 
    • biofuels e.g. wood produce a lot of ash when they burn
  • A good fuel must burn easily (ease of ignition) 
    • easily ignited fuels can also be more dangerous
  • Solid fuels e.g. coal are easy to store but harder to transport - lorry/train
  • Liquid + gas fuels must be stored in tanks but can be transported in pipes
    • methane + hydrogen must be stored at high pressures
  • Hyrdrogen powered cars - only when hydrogen is economically available
    • filling stations would have petrol diesel AND hyrdrogen - EXPENSIVE
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Alkanes and Alkenes

  • Alkanes - hydrocarbons with only single carbon-carbon bonds 
    • e.g. methane, ethane, propane
  • Alkenes - hydrocarbons with one double carbon-carbon bond
    • e.g. ethene, propene
  • Alkane molecule - each carbon atom is joined to four other atoms with single bonds 
  • Alkene molecule - one pair of carbon atoms are double bonded with 2 other bonds and other carbon atoms have 4 single bonds
  • Saturated hydrocarbons - hydrocarbons with all single, carbon-carbon bonds
    • alkanes are saturated hydrocarbons
  • Unsaturated hydrocarbons - hydrocarbons with double bonds in their molecules
    • alkenes are unsaturated hydrocarbons
  • Methane - 1 carbon 4 hydrogen (simplest alkane)
  • Ethane - 2 carbon 6 hydrogen
  • Propane - 3 carbon 8 hydrogen
  • There are 2 hydrogen atoms for every 1 carbon atom PLUS one on each end
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Alkanes and Alkenes Continued


  • Bromine water - bromine dissolved in water, usually orange
  • Bromine test - used to find out if a compound contains double bonds
    • mixed with a saturated hydrocarbon - no reaction - NO COLOUR CHANGE
    • mixed with an unsaturated hydrocarbon - reacts with alkene - DECOLORISES
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  • Cracking - splitting up longer hydrocarbons into shorter, more useful ones
  • Long-chain alkanes heated and break into smaller molecules
    • example of thermal decomposition - broken up by heat
    • energy to heat alkanes comes from burning fossil fuels
  • Cracking produces shorter-chain alkanes and alkenes
    • always the same amount of carbon and hyrdogen atoms before and after
    • shorter-chain alkanes used for fuels e.g. petrol
    • most alkenes used for plastics
  • When they split theres not enough hydrogen atoms to go around
    • causes one molecule to be unsaturated
    • double bonded carbon atoms
  • Different oil fields = different mixtures of hydrocarbon molecules
  • More demand for certain fractions that is made from the fractional distillation
  • Cracking kerosene and fuel oil are cracks to match demands
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  • Polymer - substance made of thousands of relatively simple repeating units
  • Monomer - substance whose molecules react together to form polymers
  • Polythene - real name poly(ethene)
    • example of a polymer
    • made of lots of ethene monomers
    • used to make plastic bags/bottles
  • Some polymers occur naturally e.g. proteins, cellulose
  • Others manufactured by cracking crude oil
    • often known as plastics
  • Polymerisation reactions - monomer molecules react to form long-chain molecules(
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Polymer Properties

  • Poly(ethene) / polythene / polyethylene
    • flexible, cheap, good insulator
    • used for plastic bags, plastic bottles, cling film, electrical wire insulation
  • Poly(propene) / polypropylene
    • flexible, shatterproof, high softening point 
    • used for buckets, bowls
  • Poly(chloroethene) / PVC
    • tough, cheap, long-lasting, good insulator
    • used for window frames, gutters, pipes, electrical wire insulation
  • Poly(tetrafluoroethene) / PTDE / Teflon
    • tough, slippery, resistant to corrosion, good insulator
    • non-stick saucepan coatings, bearings, skis, stain-proofing carpets, corrosive substance containers, electrical wire insulation
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Problems With Polymers

  • Biodegradable - a material that can rot because microbes can feed on them
  • Most manufactured polymers do not biodegrade
    • are useful because they last a long time
    • however do not rot when they are thrown away
  • Non-biodegradable plastic materials will last many years in landfill sites
  • Some waste is incinerated and energy released used to generate electricity
    • but many plastics release toxic substances when they burn
    • they can be removed from waste gases and toxic ash must be disposed of safely
  • Chemists are producing biodegradable polymers
    • they will rot after a few years of being in a landfill site
    • however will take time
    • reducing amounds of plastic in landfill sites is better
  • This can be done by reusing platic bags not throwing them away
    • when its fully reused it can be recycled
  • Polymers harder to recycle than glass, paper and metal
    • needs to be sorted into types of polymer
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