Phase Diagram

Phase Diagrams in General Chemistry 2

Learning Outcomes

  • Describe the components of a phase diagram.

  • Use phase diagrams of pure substances to determine its phase at given temperature and pressure.

  • Interpret a phase diagram.

  • Construct a phase diagram of a substance from given data.

Definition of Phase Diagram phase diagram is a graphical representation that illustrates the phases of a substance as a function of temperature and pressure, showing the conditions under which distinct phases occur and coexist.

  • Phases include:

    • Solid

    • Liquid

    • Gas

Key Concepts of Phase Diagrams

Triple Point

  • Triple Point is defined as the combination of pressure and temperature at which all three phases (solid, liquid, gas) of a substance coexist in equilibrium.

Critical Point

  • Critical Point marks the end of the liquid-gas phase boundary.

    • Beyond this point, the liquid and gas phases merge into a single phase known as a supercritical fluid. liquid and gas mixed

    • Critical Pressure and Critical Temperature define the attributes of this point.

Curves on Phase Diagrams

Melting (Freezing) Curve

  • Represented by a green line:

    • Indicates transition between solid and liquid phases.

    • Equilibrium between solid and liquid exists along this line.

Vaporization (Condensation) Curve

  • Represented by a blue line:

    • Indicates transition between liquid and gas phases.

    • Equilibrium between liquid and gas occurs along this line.

Sublimation (Deposition) Curve

  • Represented by a red line:

    • Indicates transition between solid and gas phases.

    • Equilibrium exists along this line as well.

Example: Phase Diagram for Water

  • Axis Values:

    • Pressure in atm ranges from below 0.01 atm to about 217.75 atm.

    • Temperature in °C ranges from below 0.01 °C to around 374 °C.

  • Key Features:

    • Normal freezing point at 0 °C.

    • Normal boiling point at 100 °C.

    • Shows the specific regions for solid (ice), liquid (water), and gas (water vapor).

Example: Phase Diagram for Mysterious Compound X

  • Contains similar features to water phase diagram but lacks detailed context.

  • Ranges in temperature from -100 °C to 800 °C at varying pressures.

Visualization of Phases

  • Knowing how to read and interpret the phase diagram is crucial for understanding the state of matter of a substance under different temperature and pressure conditions.