Cracking Hydrocarbons

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Cracking Hydrocarbons

Heavier fractions that we get by distilling crude oil are not very useful. The hydrocarbons in them are made of large molecules. They are thick solids and liquids with high boiling points. They are difficult to vaporise and do not burn easily - so they are no good as fuels. Yet the main demand from crude oil is for fuels.

Luckily we can break down large hydrocarbon molecules in a process called cracking. The process takes place at an oil refinery in a steel vessel called a cracker.

In the cracker, a heavy fraction produced from crude oil is heated to vaporise the hydrocarbons. The vapour is then passed over a hot catalyst or mixed with steam. It is heated to a high temperature. The hydrocarbons are cracked as thermal decomposition reactions take place. The large molecules split apart to form smaller, more useful ones.

Cracking produces saturated hydrocarbons which are used as fuels and unsaturated hydrocarbons (called alkenes).

Alkenes react with orange bromine water, turning it colourless.

Remember alkanes are saturated, alkenes have a double bond = (equals)