9.4
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What is cracking
Breaking down larger, less useful hydrocarbon molecules into smaller, more useful ones
Where does cracking take place
At an oil refinery in steel vessels called crackers
What happens during cracking
• a heavy fraction distilled from crude oil is heated to vaporise the hydrocarbons. The vapour is then either: • passed over a hot catalyst (catalytic cracking) • mixed with stream and heated to a very high temperature (steam cracking)
When are the hydrocarbons cracked
As thermal decomposition reactions take place
Thermal decomposition def
The breakdown of a compound by heating it
Give one example of cracking
• decade is heated to 500 degrees with a catalyst, it breaks down to form pentane, propane and ethane • pentane is used in petrol • propane and ethane can be used to produce polymers and other chemicals such as solvents
what are the two products of cracking
alkanes and alkenes
what type of hydrocarbons are alkenes
unsaturated
what carbon bond do unsaturated carbons contain
at least one double carbon bond
are alkanes or alkenes more reactive
alkenes
what is a positive test for an unsaturated hydrocarbon
turns bromine water colourless