Question

The correct decreasing order of boiling point of hydrogen halides is

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

Answer 1

The Correct Option is C

The boiling points of hydrogen halides are determined by the type and strength of intermolecular forces, such as hydrogen bonding and van der Waals forces.

• HF (Hydrogen Fluoride): Exhibits strong hydrogen bonding due to the small size and high electronegativity of fluorine. This results in the highest boiling point among the hydrogen halides.
• HI (Hydrogen Iodide): Has a high boiling point because of the larger iodine atoms and stronger van der Waals forces, though weaker than hydrogen bonds in HF.
• HBr (Hydrogen Bromide): Has a boiling point higher than HCl due to larger bromine atoms, which result in stronger van der Waals forces.
• HCl (Hydrogen Chloride): Has the lowest boiling point as it lacks hydrogen bonding and only experiences weaker van der Waals forces.

The correct decreasing order of boiling points is: HF > HI > HBr > HCl.

Thus, the correct answer is (C).

Answer 2

The boiling point of hydrogen halides increases with the size of the halogen atom because larger halogens have stronger London dispersion forces.  

• HF has strong hydrogen bonding, resulting in the highest boiling point. 
• HI has a higher boiling point than HBr and HCl due to its larger atomic size and stronger dispersion forces.  
• HCl has the lowest boiling point due to its smaller size and weaker dispersion forces compared to the others.  

So, the correct order is: \(HF > HI > HBr > HCl\)