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
- 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
- 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
- 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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Polymerisation
- 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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