question_answer 1)

  Use the information and data given below to answer the questions (a) to (c) : (i) Stronger intermolecular forces result in higher boiling point. (ii) Strength of London-dispersion forces increases with the number of electrons in the molecule. (iii) Boiling point of \[HF,\text{ }HCl,\text{ }HBr\]and \[HI\]are 293 K, 189 K, 206 K and 238 K respectively. (a) Which type of intermolecular forces are present in the molecules \[HF,\text{ }HCl,\text{ }HBr\]and\[HI\]? (b) Looking at the trend of boiling points of \[HCl,\text{ }HBr\] and HI, explain out of dipole-dipole interaction and London interaction, which one is predominant here? (c) Why is boiling point of hydrogen fluoride highest while that of hydrogen chloride lowest?

Answer:

  (a) HF ® Hydrogen bonding \[HCl,\,\,\,HBr,\,\,HI\,\to \] Dipole-dipole interaction, London-dispersion force. (b) London-dispersion force is dominant because boiling point is not in the order of decreasing electro negativity of halogens. (c) HF involves strong intermolecular hydrogen bonding, hence its boiling point is highest.