Question

Which main intermolecular force must be overcome to sublime solid NH3?

Answer 1

To sublime solid NH3, the strong hydrogen bonding intermolecular forces must be overcome, which allows ammonia to change from solid to gas directly.

Step-by-step explanation:

The main intermolecular force that must be overcome to sublime solid ammonia (NH3) is hydrogen bonding. Ammonia molecules have hydrogen atoms bonded to nitrogen, which is a highly electronegative atom, creating a significant dipole.

The hydrogen atoms in one molecule can interact with the lone pair of electrons on the nitrogen of another molecule, forming a hydrogen bond, which is a strong type of dipole-dipole interaction. Sublimation of solid NH3 requires energy to overcome these intermolecular forces, allowing the solid to transition directly into the gas phase without becoming a liquid first.

Answer 2

Sublimation is the phase transition of a substance directly from the solid to the gaseous phase without passing through the liquid phase.

Here are the three forces that exist between two NH3 molecules:

1- Dispersion forces - these forces exist between ANY two molecules, regardless of anything else.

2- Dipole-dipole interactions - NH3 is a polar molecule with a permanent separation of charge. Each molecule behaves like a tiny magnet and has + and - poles so 2 NH3 molecules attract each other. Dipole-dipole interactions are stronger than dispersion forces in small molecules.

3- Hydrogen bonding - H is directly bonded to the extremely electro negative atoms N, O, or F, hence hydrogen atom is nearly stripped off electrons due to the large electro - negativity difference. Hydrogen being a small atom further reduces in size even allowing it to approach other molecules very closely. Here N,O,F gathers more partial negative charge.

Due to the close approach between the molecules and the strong partial charges, hydrogen bonding is generally more important than dipole-dipole interactions.

So the main intermolecular force must be hydrogen bonding.