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Chemistry Question on Group 17 Elements

The correct order of the thermal stability of hydrogen halides (H-X) is

A

HI > HCl < HF > HBr

B

HCl < HF > HBr < HI

C

HF > HCl > HBr > HI

D

HI < HBr > HCl < HF

Answer

HF > HCl > HBr > HI

Explanation

Solution

The H-X bond strength decreases from HF to HI. i.e. HF > HCl > HBr > HI. Thus HF is most stable while HI is least stable. The decreasing stability of the hydrogen halide is also reflected in the values of dissociation energy of the H-X bond
H−FH−Cl;H−Br;H−I; 135 kcal mol−1103 kcal mol−185 kcal mol−171 kcal mol−1\begin{matrix}H-F&H-Cl;&H-Br;&H-I;\\\ 135\,kcal\,mol ^{-1}&103\,kcal\,mol ^{-1}&85\,kcal\,mol ^{-1}&71\,kcal\,mol ^{-1}\end{matrix}