Specification:
-The term cracking; the use of the catalysts in cracking process; technique and procedures for cracking a hydrocarbon vapour over a heated catalyst.
What does it mean to crack and why do we use it?
Different fuels come from the fractional distillation of crude oil but they are not all in high demand like heavier fuel. Hydrocarbons are made up of large molecules and therefore we would break down the hydrocarbons to make them into smaller molecules which are used for high demand. This process is called cracking.
There are two type of cracking you need to know:
-Thermal cracking which involved a very high temperature and pressure.
-Catalytic cracking is when you use a catalyst to crack and a very high temperature. This is mainly used for plastic.
For both cracking you would get a produce that will make alkene and alkanes.
Example:
C10H22 → C6H12 + C4H12
You always need to make sure you are not losing any carbons or hydrogen atoms. They should always add up.
The benefit of a catalyst is that it will use less heat and pressure because it lowers the activation energy providing an alternative pathway. This means more molecules have more energy than the activation energy to react,so would cost less. However,the catalyst can get poisoned (stop working properly or reactants are unable to be adsorbed to the catalytic surface due to accumulation of soot/carbon particulates during incomplete combustion) and would need to get changed which can cost a lot.
Check the section of alkenes and alkanes if you don’t know the difference.
The experiment for cracking:
You would need to set up the experiment like this one above. You would have a mineral wool soaked in a fuel with long hydrocarbon chains and a catalyst in the test tube. When you heat the test tube and its contents, Evaporation occurs and then condenses in the cooling condenser. Gas has now formed.You would collect this gas in a measuring cylinder. This would be some alkene produce and on the test tube you will be left with some shorter alkanes.
To check your alkenes you would add some bromine water. If this turns to a colourless colour this would mean you have made some alkenes as only alkene will react with bromine water and not alkane.
However, if your bromine water remains orange, then you have produced an alkane.
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