Cracking Flashcards
Crude oil is a mixture of
hydrocarbons - which can be separated using fractional distillation.
Why is cracking useful?
Shorter chain hydrocarbons are more flammable and can be used for fuels,
In comparison, the longer chain, more viscous hydrocarbons are less useful.
Through cracking, we can break down these longer, less useful hydrocarbons into useful, smaller chains.
Cracking is a _________ __________ reaction
thermal decomposition
Cracking process:
Large hydrocarbon molecules are broken down by heating them and passing them over a hot catalyst. This is called cracking. Some of the molecules produced when we do this contain a double bond. They are called unsaturated hydrocarbons for this reason. They are examples of a group of hydrocarbons called the alkenes.
The shorter chain alkanes produced can be used as a fuel.
Formula for alkenes
CnH2n - unsaturated since they have a double bond between two carbon atoms
Alkenes are unsaturated hydrocarbons (like alkenes they are a homologous series) What is the difference in structure between alkenes and alkanes?
Alkenes have a double bond. This difference leads to the two important features of alkanes -> more reactive, and can be added to make polymers.
How to test for alkenes after cracking?
They react well with Bromine water to turn it from orange to colourless -> the difference in reactivity between alkenes and alkanes means that the alkane would not react with the bromine water. Therefore, if bromine water turns colourless we know for sure that alkenes are present.
Why does cracking always produce one alkene and one alkane?
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.
