Question

Why does ammonia have a higher boiling point than that of phosphine?

Answer 1

1. Ammonia (NH₃) has a higher boiling point than phosphine (PH₃) because ammonia molecules form strong intermolecular hydrogen bonds due to the high electronegativity difference between nitrogen and hydrogen.
2. Phosphine molecules do not form hydrogen bonds; they only exhibit weaker van der Waals forces.
3. These hydrogen bonds cause ammonia molecules to associate strongly, raising its boiling point.
4. In contrast, phosphine has only van der Waals forces, which are weaker and result in a lower boiling point.

Hence, ammonia’s boiling point is higher due to intermolecular hydrogen bonding, while phosphine's boiling point depends on weaker forces.