Why is ethene and bromine an addition reaction?

1 Answer
Apr 9, 2016

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 #pi#-bond, and #pi#-bonds are weaker than #sigma#-bonds. Alkenes have some strong bonds and some weak bonds, while alkanes only have strong bonds.

The equation for ethene and bromine is

#C_2H_4 + Br_2 -> C_2H_4Br_2#.

It forms dibromoethane, which is a halogenoalkane.