Why is ethene and bromine an addition reaction?
Because ethene is an alkene, which is a less stable structure than an alkane. Bromine opens the double bond in ethene, rather than replacing hydrogen. This gives ethene an alkane structure.
Ethene and bromine are an addition reaction because ethene is an alkene - it has a double bond. It is easier for new atoms to open the double bond and react there than to remove the hydrogen already attached, and then bond to it, which would be a substitution reaction.
Alkenes are more unstable than alkanes, because alkenes have double bonds, which include a
The equation for ethene and bromine is
It forms dibromoethane, which is a halogenoalkane.