[fighter127]

For example let's say there is a reaction being shown. On the left side of the arrow, there is a molecular structure with a double bond. On the right side, the double bond has disappeared and from each of the carbons the double bond was initially attached to there is a Cl atom or Br atom, etc showing a total of two Br or Cl atoms. When asked what change took place, why does the answer key say two Br atoms are added across the double bond? I guess the wording just doesn't make sense to me. Does it mean that one of the bonds is being removed, creating a single bond? If anyone could explain this it would be much appreciated!

[spirochete]

The carbon carbon pi bond has been broken, and each carbon atom that used to be pi bonded now has a new single bond to something. HBr, the components of water (H and OH), H₂ and many other things can be added across a double bond.

None of this really has to be explained though, if you just look at examples of reactants and products it should become clear.