Question

Use the information and data given below to answer the questions

• Stronger intermolecular forces result in higher boiling point

• Strength of London forces increases with the number of electrons in the molecule • Boiling point of HF ,HCl, HBr and HI are 293K,189K,206K and 238K respectively

(a) Which type of intermolecular forces are present in the molecules HCl, HBr and HI?

(b) Looking at the trend of boiling points of HCl, HBr and HI, explain, out of dipole interaction and London interaction, which one predominant here?

(c) Why is the boiling point of HF highest while that of HCl lowest?

Answer 1

(a) In the molecules HCl, HBr and HI, dipole-dipole interaction and London forces are present.

(b) Dipole moment of HCl > HBr > HI but boiling point of HCl < HBr <HI.It means London forces are predominant over dipole-dipole interaction which depends upon surface area.HCl has least surface area, Whereas HI has maximum surface area.

(c) HF has highest dipole moment due to highest difference in electronegativity, therefore hydrogen bonding is also present due to which force of attraction will increase, hence it has higher boiling point.