Question

The CORRECT order of boiling points for the hydrogen halides is:

• A. \( HF>HI>HBr>HCl \)
• B. \( HF>HCl>HBr>HI \)
• C. \( HI>HBr>HCl>HF \)
• D. \( HI>HF>HBr>HCl \)

Hint:

In comparing the boiling points of hydrogen halides, remember that hydrogen bonding in {HF} greatly increases its boiling point. For the other hydrogen halides, molecular size and polarizability are the key factors.

Answer 1

The Correct Option is A

The boiling points of hydrogen halides are determined by the type of intermolecular forces that exist between the molecules. The primary factors affecting the boiling point of hydrogen halides are hydrogen bonding, size of the halide, and molecular weight. 
1. Hydrogen Bonding: 
HF exhibits the strongest intermolecular forces among the hydrogen halides because of the strong hydrogen bonding between HF molecules. This leads to a significantly higher boiling point for HF compared to the others. 
2. Molecular Size and Polarizability: 
The other hydrogen halides, HI, HBr, and HCl, primarily rely on London dispersion forces. These forces increase with the size and polarizability of the molecules. Since iodine is the largest halogen, HI has the highest boiling point after HF. 
3. Boiling Point Trend: 
HCl and HBr have similar molecular sizes, but HBr has a slightly higher boiling point than HCl due to its larger size and greater polarizability. Thus, the correct order of boiling points is: 
\[ HF>HI>HBr>HCl \]