Cracking alkanes to make alkenes
Short chain hydrocarbons (alkanes) are very useful. Especially for fuels.
Long chain hydrocarbons (alkanes) aren't as useful.
WE CRACK A LONG ALKANE TO MAKE A SHORTER ALKANE AND AN ALKENE
The wool is soaked in paraffin (made up of long hydrocarbons/alkanes). This evaporates at the start and when it meets the porcelain bits (the catalyst) it THERMALLY DECOMPOSES (breaks down chemically because of heat). The product is a gas made up of a shorter ALKANE and an ALKENE, seen below:
The shorter hydrocarbon is much more useful as it has a higher flammability and can now be added to petrol.
The ALKENE contains a double bond therefore it's UNSATURATED
The test for unsaturated (ALKENE) hydrocarbons
Bromine water turns colourless when it meets unsaturated hydrocarbons but stays orange when it meets saturated hydrocarbons (without double bonds - alkanes)
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