Chapter 11: Intermolecular Forces and Phases

Introduction

• Focus on intermolecular forces and phases of substances.
• Intermolecular force: attractive force between separate molecules (not a chemical bond).
• Example: Water in zero-gravity forms little spheres due to intermolecular forces.
• Different phases depend on the strength and type of intermolecular forces.

Phases of Matter

• Gases
  • Low density
  • Weak intermolecular forces
  • Take shape and volume of container
  • Compressible
• Liquids
  • Moderate intermolecular forces
  • Definite volume, takes shape of container
  • Incompressible
• Solids
  • Strong intermolecular forces
  • Definite shape and volume
  • Incompressible
  • Two types: Crystalline (orderly) and Amorphous (disordered)

Intermolecular Forces

• Dispersion Forces (London forces)
  • Present in all molecules
  • Temporary dipoles
  • Increase with molar mass
• Dipole-Dipole Forces
  • Between polar molecules
  • Permanent dipoles
• Hydrogen Bonding
  • Strong dipole-dipole interaction
  • Occurs with H bonded to N, O, or F
• Ion-Dipole Forces
  • Mix of ionic compounds and polar molecules
  • Strong, affect solubility in water

Properties Affected by Intermolecular Forces

• Surface Tension
  • Results from tendency to minimize surface area
  • Higher with stronger intermolecular forces
• Viscosity
  • Resistance to flow
  • Higher with stronger intermolecular forces
• Capillary Action
  • Ability to flow against gravity in a thin tube
  • Depends on cohesive and adhesive forces

Phase Changes

• Vaporization and Condensation
  • Vaporization: Liquid to gas, endothermic
  • Condensation: Gas to liquid, exothermic
• Sublimation and Deposition
  • Sublimation: Solid to gas
  • Deposition: Gas to solid
• Fusion (Melting) and Freezing
  • Fusion: Solid to liquid, endothermic
  • Freezing: Liquid to solid, exothermic

Dynamic Equilibrium

• Occurs when rate of vaporization equals rate of condensation in a closed system.
• Vapor pressure: Pressure of a vapor in equilibrium with its liquid.
• Affected by intermolecular forces and temperature.

Boiling Point and External Pressure

• Boiling occurs when vapor pressure equals external pressure.
• Normal boiling point: Vapor pressure equals 1 atm.
• Boiling point varies with external pressure.

Calculations and Thermodynamics

• Clausius-Clapeyron Equation
  • Used for calculating vapor pressures
• Heating Curve: Tracks energy changes in phase transitions.
  • Segments: Solid heating, fusion, liquid heating, vaporization, gas heating
  • Calculations involve Q = mCΔT for temperature changes and ΔHvap or ΔHfus for phase changes.

Phase Diagrams

• Graphical representation of phases at different temperatures and pressures.
• Triple Point: All three phases coexist.
• Critical Point: End of liquid-gas phase boundary.
• Supercritical Fluid: Hybrid properties of liquids and gases.

Unique Properties of Water

• High surface tension and specific heat
• Excellent solvent due to dipole moment
• Expansion upon freezing creates less dense solid than liquid

This summary captures the essential concepts of Chapter 11 about intermolecular forces, their effects on the properties of substances, and the transitions between different phases. Be sure to understand the differences between types of intermolecular forces and how they affect boiling points, solubility, and other physical properties.