Chapter 12: Intermolecular Forces and the Physical Properties of Liquids and Solids (Properties of Liquids and Phase Change)

Vocabulary flashcards covering key terms related to liquids and phase changes from the lecture notes.

Surface tension

Energy required to stretch or increase the surface area of a liquid by a unit area; stronger intermolecular forces lead to higher surface tension.

Lotus effect

Surface phenomenon where the surface film of a liquid tends to minimize surface area, related to surface tension effects on wetting.

Capillary action

Movement of a liquid up a narrow tube due to adhesive forces between the liquid and the tube being stronger than cohesive forces within the liquid.

Cohesion

Attraction between like molecules (e.g., water–water).

Adhesion

Attraction between unlike molecules (e.g., water–glass).

Cohesive forces

Attractive forces between like molecules within a liquid.

Adhesive forces

Attractive forces between unlike molecules, such as liquid to a solid surface.

Hydrophobic

Water-repelling; tends to have poor wetting and high contact angles.

Hydrophilic

Water-attracting; tends to wet surfaces well and have low contact angles.

Contact angle

Angle where a liquid–solid interface meets the liquid's surface; high angle means poor wetting, low angle means good wetting.

Wettability

ease with which a liquid spreads over a solid surface; related to contact angle and adhesive interactions.

Viscosity

Measure of a fluid’s resistance to flow; higher viscosity means slower flow and is influenced by intermolecular forces.

Vapor pressure

Pressure exerted by vapor in equilibrium with its liquid at a given temperature; increases with temperature and depends on intermolecular forces.

Vaporization

Phase change from liquid to gas when molecules escape from the liquid surface.

Evaporation

Vaporization that occurs at the surface below the boiling point; not restricted to the boiling point.

Condensation

Phase change from gas to liquid.

Dynamic equilibrium

Situation where forward (evaporation) and reverse (condensation) processes occur at equal rates, system appears unchanging.

Boiling point

Temperature at which a liquid’s vapor pressure equals the external atmospheric pressure.

ΔHvap

Molar heat of vaporization; energy required to vaporize 1 mole of a substance at its boiling point.

Clausius–Clapeyron equation

Relation between vapor pressure and temperature: ln P = −ΔHvap/(R T) + C; shows how P changes with T for phase changes.

Gas constant (R)

Universal gas constant, 8.314 J/(K·mol), used in the Clausius–Clapeyron equation.

Temperature

Measure of thermal energy; in CC equation, linked to changes in vapor pressure.

1/T (reciprocal temperature)

Axis used in plotting ln P versus 1/T in the Clausius–Clapeyron analysis.

Two-point form of Clausius–Clapeyron equation

Rearranged CC equation using two points: ln(P2/P1) = −(ΔHvap/R)(1/T2 − 1/T1).

Phase

A homogeneous part of a system distinct from other parts by a boundary (solid, liquid, gas).

Phase change

Transition of a substance from one phase to another (e.g., melting, freezing, vaporization, condensation, sublimation, deposition).

Freezing

Liquid to solid; energy is released.

Melting (fusion)

Solid to liquid; energy is absorbed.

Sublimation

Solid to gas; energy is absorbed.

Deposition

Gas to solid; energy is released.

ΔHfus

Molar enthalpy of fusion; energy required to melt 1 mole of a solid.

ΔHsub

Molar enthalpy of sublimation; energy required to sublime 1 mole of a solid; equals ΔHfus + ΔHvap.

Phase diagram

Graph showing the conditions (P and T) under which a substance exists as solid, liquid, or gas; includes the triple point.

Triple point

Unique combination of pressure and temperature where solid, liquid, and gas coexist in equilibrium.

Normal boiling point

Boiling point at 1 atm pressure.

Normal melting point

Melting point at 1 atm pressure.

Heating curve

Graph of temperature versus time showing heating and plateaus during phase changes.