Alkane + Br2/Heat + NaOH/Water -> Alkene
In the first part HBR is created and the second BR takes place of H
In the second step, OH takes a H adjacent to the BR, the electron in the H bond bounces down and forms a double bond, and the BR is kicked out.
An addition example would be:
Alkene + H2/PdC ->Alkane
The double CC bond is broken, and a H is added to each C