Chapter 12: Intermolecular Forces: Liquids, Solids, and Phase Changes

A set of practice flashcards covering key concepts from the provided notes on intermolecular forces, phase changes, vapor pressure, and related topics.

What is the difference between intramolecular forces and intermolecular (nonbonding) forces?

Intramolecular forces act within a molecule; intermolecular forces act between molecules and govern phase behavior.

Which forces arise from attractions between molecules with partial charges or between ions and molecules?

Intermolecular (nonbonding) forces.

Name the four main nonbonding forces discussed in this chapter.

Ion-dipole, hydrogen bonding, dipole-dipole, and dispersion (London) forces.

What is the van der Waals distance and how is the van der Waals radius defined?

The distance between two nonbonded atoms in adjacent molecules; the van der Waals radius is half that distance and is larger than the covalent radius.

How do covalent radii and van der Waals radii trend across a period and down a group?

Both decrease across a period and increase down a group.

Among nonbonding forces, which has the highest energy range?

Ion-dipole forces (roughly 40–600 kJ/mol).

What governs the strength and arrangement of hydrogen bonds, and which atoms can partake?

A hydrogen atom covalently bonded to N, O, or F forms an attraction to a lone pair on N/O/F of another molecule; hydrogen bonds are stronger than typical dipole-dipole forces and raise boiling points.

What is the role of hydrogen bonding in boiling points?

Substances exhibiting hydrogen bonding generally have exceptionally high boiling points.

What is vapor pressure?

The pressure exerted by the vapor in dynamic equilibrium with a liquid; at equilibrium, vapor pressure is constant.

How does temperature affect vapor pressure and the strength of intermolecular forces?

As temperature rises, more molecules enter the vapor phase, so vapor pressure increases; weaker intermolecular forces yield higher vapor pressures.

What is the Clausius–Clapeyron equation used for?

Relates vapor pressure to temperature; the two-point form uses P1, P2, T1, T2 with slope equal to −ΔHvap/R.

What is the normal boiling point?

The temperature at which a liquid’s vapor pressure equals standard atmospheric pressure (760 torr).

What factors affect dispersion forces and boiling point in nonpolar molecules?

Dispersion forces grow with larger, more polarizable particles; polarizability correlates with molar mass; more surface area and favorable shape increase contact and dispersion, raising bp.

What is sublimation and deposition?

Sublimation is solid to gas; deposition is gas to solid.

What are the six phase changes and their general enthalpy directions?

Melting/fusion (solid to liquid) and freezing (liquid to solid) involve ±ΔHfus; Vaporization (liquid to gas) is endothermic (+ΔHvap); Condensation (gas to liquid) and deposition (gas to solid) are exothermic (−ΔH).

What is the difference between a phase and a phase change in terms of energy flow?

Within a phase, heat changes temperature; during a phase change, heat flows at constant temperature as particles rearrange.

How does vapor pressure relate to temperature and intermolecular forces?

Vapor pressure increases with temperature and decreases with stronger intermolecular forces.

What is the relationship between boiling point and vapor pressure/forces for similar molar mass substances?

Stronger intermolecular forces or higher dipole moments raise boiling points; weaker forces lower boiling points.

How does molecular shape influence dispersion forces and boiling point (e.g., hexane vs 2,2-dimethylbutane)?

More surface contact and elongated shapes increase dispersion forces and boiling point; compact shapes have fewer contact points and lower dispersion strength.

What is dynamic equilibrium in a closed liquid-vapor system?

A state where molecules are leaving and entering the liquid at the same rate, giving a constant vapor pressure.

What is the significance of the normal boiling point and external pressure on boiling point?

Normal boiling point is at 760 torr; increasing external pressure raises the boiling point.