The Student Room Group
Reply 1
Hi, I'm not sure if your talking about the right chemicals here BUT the hydrogen halides that you have mentioned are all gases as they have very low boiling points:

Boiling Points: HI = -35, HBr = -66 and HCl = -85

but I preassume they can decompose and the most obvious decomposition would be:

2HX --------> H2 + X2 (where X = Cl, Br, or I)
HI is less stable to heat than HBr and HBr is less stable than HCl (which is stable)

HI decomposes to the elements as shown above...

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