Question

Give reasons for the following:

(i) Bond enthalpy of F₂ is lower than that of Cl₂.

(ii) PH₃ has lower boiling point than NH₃.

Answer 1

(i) Bond enthalpy of F₂ is lower than that of Cl₂ because F atom is small in size and due to this the electron-electron repulsions between the lone pairs of F-F are very large. Thus, the bond dissociation energy of F₂ is lower than that of Cl₂.

(ii) PH₃ has lower boiling point than NH₃ because NH₃ molecule possess intermolecular hydrogen bondings which binds them strongly whereas PH₃ has weaker Vander Waal’s forces. Thus, PH₃ has lower boiling point than NH₃.