In cracking the first step is always to heat and vaporise hydrocarbons into a gas.
Then in catalytic cracking hot powdered aluminium oxide would be ready as our catalyst. We would pass it over the catalyst. The long chains would split apart.
However in steam cracking we would mix the vapor with steam and heat to a very high temperature. This causes the long chains to split apart.
Cracking word equation:
Long chain alkane ---> shorter alkane + alkene
IMPORTANT- number of carbons and hydrogens has to be the same on each side.
Decane, C10H22 can be cracked into Ethene C2 H4 and one other hydrocarbon. Write a balanced equation for this reaction.
C10H22 ---> C8H18 +C2H4
Alkenes are another example of a homologous series. Alkenes are unsaturated as they have double bonds. Alkenes are more reactive than alkanes.
The test for alkenes is to add bromine water to a solution and see if the orange water is decolourised from orange to colourless.
Alkenes can be added to form polymers because the double bond can break to form two or more bonds. This means they can bond to the adjacent molecules.
cracking is a thermal decomposition reaction because it involves using heat to break something apart.
When a long chain alkane is cracked, there aren't enough hydrogen atoms to make two alkanes. Hence, cracking will always produce one alkane and one alkene. (Alkenes are hydrocarbons with a double bond between two carbon atoms).
