6th edition, 5J11

[Elizabeth Gallmeister 1A]

Part (b) concerns the equation X2 <-> 2X, where X is a halogen. Does X being a halogen tip us off as to whether the reaction is exothermic or endothermic? If yes, why?

[Brian Chhoy 4I]

Im not too sure, but considering the fact that diatomic halogens are more stable than the products, I would assume that the reaction of the decomposition is endothermic since you would have to put additional energy into the reaction to break the bond and make it go from a stable state to a less stable state.

[Matthew Tran 1H]

You could also infer that X2 is more energetically stable than X when X is a halogen because what you find in the natural world is X2, not X. If you think back to Chem 14A, halogen atoms bond to form diatomic molecules because they are more stable. The same thing goes for gases like N2 and O2 which are more stable when bonded than when they are just individual atoms.