Question

Which molecule is expected to have the higher boiling point and why?

HF vs. HBr
(hint: both the H-F and H-Br bonds are polar covalent)

a. HF because it has hydrogen bonding IMFs and HBr does not have hydrogen bonding IMFs.
b. HBr because it has hydrogen bonding IMFs and HF does not have hydrogen bonding IMFs.
c. HBr because it has London Dispersion IMFs and HF does not have London Dispersion IMFs.
d. HF because it has London Dispersion IMFs and HBr does not have London Dispersion IMFs.

Answer 1

HF has a higher boiling point than HBr due to the presence of hydrogen bonding intermolecular forces in HF, which are not present in HBr.

Step-by-step explanation:

The molecule expected to have a higher boiling point between HF (hydrogen fluoride) and HBr (hydrogen bromide) is HF because it has hydrogen bonding intermolecular forces (IMFs), whereas HBr does not have hydrogen bonding IMFs. Hydrogen bonds are a type of strong dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like fluorine. This results in a significant increase in boiling point for molecules capable of hydrogen bonding.

HF is able to form hydrogen bonds because it has a hydrogen atom bonded to fluorine, which is highly electronegative. HBr does not exhibit hydrogen bonding because bromine is not as electronegative and hence the H-Br bond is not polar enough to lead to hydrogen bonding. Molecules like HF that can form hydrogen bonds typically have anomalously high boiling points compared to molecules that do not have this capability.