Chemistry - 1.4 - Crude Oil and Fuels - Revision Cards in GCSE Chemistry

C1.4.1 - Fuels from Crude Oil

Crude oil - many different compounds with different boiling temperatures - burn under different conditions so have to be separated to be useful
Separation of liquids can be done by distillation - simple crude oil distillation produces liquids that boil within different temperature ranges - these liquids are called fractions
Most compounds in crude oil are hydrocarbons - many are alkanes (CnH2n+2) - alkanes ontain as many hydrogen atoms as possible so are called saturated hydrocarbons
Molecules are represented in different ways - molecule formula shows number of each atom in the molecule, displayed formula shows how atoms are bonded together

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Crude oil - separated using fractional distillation - boiling point of a hydrocarbon depends on the chain length - larger molecule = higher boiling point
Crude oil is vapourised -> vapour is put into column (tower - hotter at bottom; cooler at top) -> vapours move up the column getting cooler as they go up (holes in column allow gases through) -> hydrocarbons condense to liquids when they reach their boiling point -> different liquids collect on trays at different points -> outlets to collect fractions
Smallest molecule = lowest boiling point - collected at top, fractions at the bottom contain long chain hydrocarbons with high boiling points
Low boiling point = low viscosity (runny liquids), flammable, burn with clean flames (little smoke) - useful fuels

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Pure hydrocarbons oxidise to CO2 and H2O when burnt completely - not always burnt completely and may contain other substances
Incomplete combustion - limited air supply -> CO is produced - carbon may be produced and some of the hydrocarbons may not burn -> produces colid paricles containing soot (carbon) and unburnt hydrocarbons - paticulates
Sulfur dioxide - fossil fuels containing sulfur compounds burn to produce sulfur dioxide - this causes acid rain
Nitrogen oxides - high temperatures produced when burning fossil fuels make O and N combine to form NO2 - also cause acid rain

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Burning fuels produces substances that affect the environment
Any fuel containg carbon burns to make CO2 - greenhouse gas believed to cause global warming, incomplete combustion = CO - poisonous gas, can prouce tiny solid particules that reflect sunlight and cause global dimming
SO2 and NO2 produced - dissolve in water and react with O2 in the air = acid rain
Removing substances from waste gases - sulfur dioxide removed from waste gases from power stations, catalytic converters in exhaust systems in cars remove CO and NO2, filters remove partculates, sulfur removed from fuels before sold so less SO2 is produced

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Biofuels - made from plant or animal products, renewable, biodiesal can be made from vegetable oils extracted from plants
Adv of biodeisel - little CO2 level contribution - plants took it in when growing
Disadv of biodeisel - plants grown take up large areas
Ethanol made from dugar cane or sugar beet - biofuel - liquid so sored and distributed like other liquid fuels, can be mixed with petrol
Hydrogen as fuel - only produces water when burnt, gas -> large volume - difficult to store in needed quantities, can be produced from water by electrolysis but requires large amounts of energy

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