Why is ammonia a gas at room temperature?

Why is ammonia a gas at room temperature?

• A. Weak intermolecular forces
• B. Strong covalent bonds
• C. Large molecular mass
• D. Ionic bonds

Answer: (A)

The important idea is how strong the attractions are between different molecules compared with the molecules’ own motion at room temperature. Ammonia is a small, light molecule, and the forces between separate NH3 molecules are relatively weak. Because of this, the thermal energy of the molecules at room temperature is enough for them to escape one another and exist as a gas. Inside each molecule, the atoms are held together by covalent bonds, which are strong, but those bonds stay within the molecule rather than between molecules. If the intermolecular forces were stronger or the molecules heavier, ammonia would be more likely to be a liquid or solid at room temperature. The fact that ammonia boils at about -33°C shows these intermolecular attractions are not strong enough to keep it liquid at room temperature.

The important idea is how strong the attractions are between different molecules compared with the molecules’ own motion at room temperature. Ammonia is a small, light molecule, and the forces between separate NH3 molecules are relatively weak. Because of this, the thermal energy of the molecules at room temperature is enough for them to escape one another and exist as a gas. Inside each molecule, the atoms are held together by covalent bonds, which are strong, but those bonds stay within the molecule rather than between molecules. If the intermolecular forces were stronger or the molecules heavier, ammonia would be more likely to be a liquid or solid at room temperature. The fact that ammonia boils at about -33°C shows these intermolecular attractions are not strong enough to keep it liquid at room temperature.