Phase Diagrams

Phase Diagrams

• Graphical representation relating pressure and temperature to the state of matter for a substance.

• Axes:

  • Y-axis: Pressure (increases upwards)

  • X-axis: Temperature (increases rightwards)

Key Features of Phase Diagrams

• State of Matter: Determine solid, liquid, or gas at specific temperature and pressure.

• Example (Water):

  • Standard atmospheric pressure: 1 atm or 101.3 kPa.

  • Freezing point: 0°C (intersection of solid and liquid boundary).

  • Boiling point: 100°C (liquid to gas line at 1 atm).

Important Points

• Boundary Lines:

  • Solid ↔ Liquid: Melting/Freezing point.

  • Liquid ↔ Gas: Boiling point.

  • Solid ↔ Gas: Sublimation.

• Triple Point:

  • All three states (solid, liquid, gas) coexist.

  • Occurs at low pressure and low temperature for water.

• Critical Point:

  • No distinction between liquid and gas beyond this point.

  • Formation of supercritical fluids occurs here.

State Changes

• Can change states by:

  • Heating: Increasing temperature raises phase.

  • Pressure Change: Lowering pressure can change state without temperature change.

• Example of Pressure Change:

  • Using a bell jar to create a vacuum lowers pressure and can boil liquid at constant temperature.

Comparison of Phase Diagrams

• Unique phase diagrams for different substances based on properties.

• Example:

  • Water (H2O) changes from solid to liquid at 0°C at 1 atm.

  • Carbon Dioxide (CO2) sublimates from solid to gas at 1 atm (e.g., dry ice emitting vapor).

• Phase diagrams illustrate how temperature and pressure manipulations can alter the state of a substance.