Question

Which substance has the higher boiling point? Explain.

(a) LiCl or HCl (b) ${\mathbf{NH}}_{\mathbf{3}}$or data-custom-editor="chemistry" ${\mathbf{PH}}_{\mathbf{3}}$ (c) Xe ordata-custom-editor="chemistry" ${\mathbf{I}}_{\mathbf{2}}$

Short answer

1. LiCl or HCl: LiCl vapour pressure is lower than the HCl.
2. ${\mathbf{NH}}_{\mathbf{3}}$or ${\mathbf{PH}}_{\mathbf{3}}$: ${\mathbf{NH}}_{\mathbf{3}}$vapour pressure is lower than the ${\mathbf{PH}}_{\mathbf{3}}$.
3. Xe or ${\mathbf{I}}_{\mathbf{2}}$: Xe vapour pressure is lower than the ${\mathbf{I}}_{\mathbf{2}}$.

Step-by-step solution

Intermolecular Forces 

Intermolecular forces are the interaction which are formed by the attraction of the two having opposite charges (partial positive and partial negative charge). The opposite charge are formed by the presence of the electron-negative atom in the molecule. Due to the presence of an electron-negative atom, there is and induced partial positive charge is generated on the electron-positive charge (or less electron-negative charge) atom. There will be an attraction between the both oppositely charges to form a bond.

Hydrogen bonding: These types of interactions are present in the electropositive and electronegative atom. There are the interaction between the oppositely charged atom which are induced by the presence of the electronegative atom.

Inter-particle interaction Explanation

Theinter-particle interaction is a type of attraction between the atoms in the molecule.

(a) LiCl or HCl:The molecule LiCl and HCl have the ionic bond in between. The ionic bond is strong in LiCl than HCl. The Electronegativity of Li-atom is less than H-atom. Therefore, the difference between the electronegativity of the LiCl is more than the HCl. As, the force of attraction is more in LiCl that’s why the boiling point is higher than HCl.

(b)${\mathbf{NH}}_{\mathbf{3}}$or ${\mathbf{PH}}_{\mathbf{3}}$:The molecule ${\mathbf{NH}}_{\mathbf{3}}$have a hydrogen bond in between. The polar hydrogen bond is strong in ${\mathbf{NH}}_{\mathbf{3}}$than ${\mathbf{PH}}_{\mathbf{3}}$. The Electronegativity of N-atom is more than P-atom. Therefore, the difference between the electronegativity of the${\mathbf{NH}}_{\mathbf{3}}$is more than the ${\mathbf{PH}}_{\mathbf{3}}$. As the force of attraction is more in ${\mathbf{NH}}_{\mathbf{3}}$that’s why the boiling point is higher than${\mathbf{PH}}_{\mathbf{3}}$ .

(c) Xe or ${\mathbf{I}}_{\mathbf{2}}$: The Xe-atom has more boiling point than. The Xe-atom has noble gas characteristics due to which it is difficult to bond distortion and the molecule has London dispersion force which has induced dipole force.