Question

What can alkenes be used for?

Answer 1

Fot quite a lot of things, because the double bond is reasonably reactive.

Explanation:

It can be broken open in an addition reaction like
`CH_2=CH_2+Cl_2->CHCl-CHCl`

Even water can react (given the right circumstances):
`CH_2=CH_2+H_2O->CH_3-CH_2-OH`
to make commercial ethanol.

The double bond may also be opened and react with another open bond:
`....CH_2=CH_2+CH_2=CH_2+CH_2=CH_2+....`
`-CH_2-CH_2-CH_2-CH_2-CH_2-CH_2-....`
This is called polymerisation, and this how (in this case) you make polythene (from poly-ethene)