Lecture Notes: Phase Changes and Phase Equilibrium

Introduction to Phase Changes

• Phase and Density Determinants: Temperature and pressure determine the phase and density of any substance.
• Temperature-Pressure Equilibrium Graph: Shows the relationship between temperature and pressure for substances like pure water.

Key Concepts

Triple Point

• Definition: The temperature and pressure at which a substance can co-exist as a solid, liquid, and gas.
• Visual Resource: Triple Point Video

Critical Point

• Definition: The temperature above which a substance cannot exist as a liquid, regardless of pressure applied.

Phase Changes on a Temperature-Pressure Graph

• Ice Melting Process:
  • Heat applied uniformly to ice (solid) warms it to a point where it begins to melt without temperature rising until all ice is melted.
  • Graph shows temperature changes and phase transitions (solid to liquid to vapor) under constant pressure.

Phases of Matter

• Solid: High density, low energy, tightly packed molecules, high potential energy (more bonds), low kinetic energy.
• Liquid: Medium density, medium energy, particles flow, medium potential and kinetic energy.
• Gas: Low density, high energy, particles move very quickly, high kinetic energy.

Phase Changes Explained

• Definition: Transition from one state of matter (solid, liquid, gas) to another.
• Nature of Phase Changes:
  • Physical changes, reversible.
  • Substance-specific energy (latent heat) required for phase changes.
  • Energy absorbed or released during phase changes.

Types of Phase Changes

• Melting: Solid to liquid (endothermic, absorbs heat).
• Freezing: Liquid to solid (exothermic, releases heat).
• Vaporization (Boiling): Liquid to gas (endothermic, occurs at boiling point).
• Condensation: Gas to liquid (exothermic).
• Sublimation: Solid to gas (endothermic).
• Deposition: Gas to solid (exothermic).

Phase Change Points

• Melting/Freezing Point: 0°C or 32°F for water.
• Vaporization/Condensation Point: 100°C or 212°F for water.
• Phase Change Info: During phase change, temperature remains constant; energy is either added or removed.

Energy Dynamics During Phase Changes

• Temperature Change (Warming/Cooling):
  • Kinetic Energy: Increases or decreases.
  • Potential Energy: Stays the same.
• During Phase Change:
  • Kinetic Energy: Stays the same.
  • Potential Energy: Increases or decreases as intermolecular forces are altered.

Additional Notes

• Phase Equilibrium: Represents balance at which phase changes occur naturally without net energy change in the system.