Question

Use the information and data given below:

• Boiling point of \[\ce{HF, HCl, HBr and HI}\] are 293 K, 189 K, 206 K and 238 K respectively.

Why is boiling point of hydrogen fluoride highest while that of hydrogen chloride lowest?

Answer 1

F atom has highest electronegativity so it has hydrogen bonding interaction in addition to dipole-dipole and london dispersion interaction which leads to the highest boiling point of \[\ce{HF}\] whereas \[\ce{HCl}\] has lowest boiling point because london force plays the predominant role in boiling point than dipole-dipole interaction and london force increases proportionally with the molecular weight of the compound. \[\ce{HCl}\] has lowest molecular weight among \[\ce{HCl, HBr and HI}\] therefore it has the least london force interaction which leads to the lowest boiling point.