Chemistry Unit 1

Cracking Crude Oil

Long-chain hydrocarbons form thick gloopy liquids
Longer moleules produced from fractional distillation are made smaller using a process called cracking
Products of cracking are useful for fuels : petrol-cars, parrafin-jet fuels
Cracking also produces substances like ethene used for making plastics
Cracking is a thermal decomposition reaction (breaking down molecules by heating them)
1. heat to vaporise (turn into a gas)
2. vapour passed over (aliminuim oxide) powdered catalyst (temp 400*c- 700*c)
3. long chain molecules split apart or "crack" on surface of catalyst
Products of cracking are alkanes and alkenes (unsaturated hydrocarbons)
Alternative way of cracking: mix the vapour with steam at a vert high temperature.

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are hydrocarbons which have a double bond between two of the carbon atoms in their chain
unsaturated because they can make more bonds
general formula Cn H2n - twice as many hydrogens as carbons
first two alkenes: ethene, propene
bromine water + alkene = colourless
ethene reacts with steam to make ethanol (using a catalyst)
cheap process not much waste
ethene comes from crude oil which is non-renewable and means will be expensive in the future
ethanol produced from renewable resources = fermentation
word equation : sugar = carbon dioxide + ethanol
needs lower temperature and simpler equiptment
poor countries benefit as they grow sugar
used as a cheap fuel in countries which don't have oil reserves for petrol
isnt very concentrated from this process - to increase strength it must be distilled and purified

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