Intermolecular Forces

What is the Kinetic-Molecular Theory?

• A theory about solids only

• It explains the behavior of gas particles

• It states that all matter is composed of molecules

• It describes chemical reactions

Answer explanation

The Kinetic-Molecular Theory specifically explains the behavior of gas particles, detailing how they move and interact. It does not apply solely to solids or describe chemical reactions.

What phase change occurs when a solid turns directly into a gas?

• Condensation

• Sublimation

• Deposition

• Freezing

Answer explanation

The phase change that occurs when a solid turns directly into a gas is called sublimation. This process skips the liquid phase, as seen in substances like dry ice, which sublimates into carbon dioxide gas.

Which of the following is NOT a type of intermolecular force?

• Hydrogen bond

• Dipole-dipole

• Ionic bond

• London dispersion forces

Answer explanation

Ionic bonding is a type of intramolecular force, involving the attraction between charged ions, while hydrogen bonding, dipole-dipole interactions, and London dispersion forces are all types of intermolecular forces.

What type of intermolecular force is responsible for the high boiling point of water?

• London dispersion forces

• Dipole-dipole interactions

• Hydrogen bonding

• Ion-dipole forces

Answer explanation

Water's high boiling point is primarily due to hydrogen bonding, a strong type of dipole-dipole interaction. Each water molecule can form multiple hydrogen bonds, requiring more energy to break them, thus raising the boiling point.

True or False: Gas particles strongly attract each other.

Answer explanation

False: Gas particles have weak intermolecular forces, allowing them to move freely and spread apart. This results in minimal attraction between gas particles compared to solids and liquids.

True or False: Boiling occurs when vapor pressure equals atmospheric pressure.

Answer explanation

True. Boiling occurs when the vapor pressure of a liquid equals the atmospheric pressure, allowing bubbles to form and rise to the surface.

True or False: London dispersion forces are the strongest intermolecular force.

Answer explanation

False: London dispersion forces are the weakest intermolecular forces. The strongest are hydrogen bonds, followed by dipole-dipole interactions.

True or False: Electronegativity determines bond polarity.

Answer explanation

True. Electronegativity measures an atom's ability to attract electrons in a bond. A difference in electronegativity between two atoms leads to bond polarity, with the more electronegative atom pulling electron density towards itself.

Which phase change requires an input of energy?

• Freezing

• Deposition

• Condensation

• Evaporation

Answer explanation

Evaporation is the phase change where a liquid turns into a gas, requiring energy input to overcome intermolecular forces. In contrast, freezing, deposition, and condensation release energy.

Why does NH3 have stronger intermolecular forces than PH3?

• NH3 has hydrogen bonds

• PH3 has a higher molecular weight

• PH3 is more electronegative

• NH3 is non-polar

Answer explanation

NH3 has stronger intermolecular forces than PH3 because NH3 can form hydrogen bonds due to the presence of a highly electronegative nitrogen atom. In contrast, PH3 lacks this capability, resulting in weaker van der Waals forces.