Question

The correct order of thermal stability of halogen halides is:

• A. $HI>HBr>HCl>HF$
• B. $HF>HCl>HBr>HI$
• C. $HCl<HF<HBr<HI$
• D. $HI>HCl<HF<HBr$

Answer 1

The correct option is B $HF>HCl>HBr>HI$

On moving down the group, the bond dissociation enthalpy $\left({\Delta }_{diss}H\right)$ of $H-X$ bond (where $X=F,Cl,Br,I$) decreases and hence thermal stability also decreases. Therefore, the correct order of thermal stability of hydrogen halides is:
$HF>HCl>HBr>HI$

Molecule	${\Delta }_{diss}H$ (in kJ/mol)
$HF$	$574$
$HCl$	$432$
$HBr$	$363$
$HI$	$295$