3.8 describe the addition reaction of alkenes with bromine, including the decolourising of bromine water as a test for alkenes

1) ethene + bromine water -> dibromoethane
2)
photo is in omers phone, havent received it yet
3)Explain the observations
It turns from red/brown to colourless. This is because the concentration of the bromine reactant decreases while the concentration of the product decreases (colourless).
4) Why does this reaction not need a catalyst?
It does not need a catalyst because ethane contains an unsaturated carbon-carbon double bond which is highly reactive and can be broken down without the influence of a catalyst.
5)What type of reaction is this called?
Addition reaction
6)Explain why this reaction is useful
This reaction is useful because it allows you distinguish between alkane and alkene using a chemical test.