LESSON-5-6 Phase Diagrams

Understanding Phase Diagrams

• Definition: A graphical representation showing stable phases of a substance under varying temperatures and pressures.

• Regions: Each phase (solid, liquid, gas) corresponds to specific conditions:

  • Solid Phase: High pressure, low temperature.

  • Gas Phase: High temperature, low pressure.

  • Supercritical Fluid: High temp & pressure.

• Phase Transition Curves: Lines separating phases show equilibrium conditions.

• Key points:

  • Triple point: All phases coexist.

  • Critical point: Differences between liquid and gas cease.

Carbon Dioxide Phase Diagram

• Features:

  • Unique sublimation behavior of solid CO2 (dry ice).

  • Triple-point pressure: 5.1 atm; liquid CO2 doesn't exist at 1 atm.

  • Solid CO2 sublimates instead of melting under ordinary conditions.

Water Phase Diagram

• Water's unique properties:

  • Solid (ice) is less dense than liquid water.

  • This results in expansion upon freezing.

  • Solid-liquid line slopes negatively indicating that higher pressure lowers freezing point.

Transition Energy Dynamics

• Heat and Phase Changes:

  • Phase transitions require significant energy without temperature change.

• Heating Curve of Water:

  • Segment BC: Melting at 0°C, temperature remains constant during this phase transition.

  • Segment DE: Boiling at 100°C, also constant temperature as gas forms.

Cooling Curves

• Cooling Curves: Graphical representation of temperature changes when cooling substances.

• Characteristics:

  • Horizontal lines indicate phase changes (condensation and freezing).

  • Reverse of heating curves.