Question

Why does the reducing power of hydrogen halides increase with increase in the atomic number of halogen?

Answer 1

1. The \[\ce{H - X}\] bond strength decreases down the group from HF to HI.
2. Larger halogen atoms form weaker \[\ce{H - X}\] bonds, making bond dissociation easier.
3. Weaker bonds lead to lower thermal stability, so the halides break down more easily to release hydrogen.
4. Easier hydrogen release increases the reducing power of hydrogen halides.
5. Consequently, HI shows the strongest reducing character, while HF shows none.

This is due to the decreased bond strength and thermal stability of hydrogen halides as the halogen’s atomic size increases down the group.