Breaking down hydrocarbons

Crude Oil

When Crude oil is separated by fractional distillation there are different amounts of each fraction.

Some fractions are more in demand than others. Oil refineries use cracking to break long chain molecules into the fractions that are more in demand. This also produces Alkenes which have a C=C double bond.

Alkenes are used to make polymers.

Cracking

Cracking involves breaking covalent bonds in hydrocarbon molecules.

Crude oil fractions are heated to evaporate them and the vapors passed over an Aluminium catalyst and heated to 650oC

For example:

Remember alkenes form a different homologous series to alkanes

Alkanes are saturated (they only have single bonds)

Alkenes are unsaturated (they contain a carbon carbon double bond.

Alkenes react with bromine water and acidified Potassium permanganate because they have a double bond to react with. They both become colourless.