Phase diagrams

Science

Definition

A phase diagram is a graph showing the stable phases (solid, liquid, gas) of a substance at different temperatures and pressures. Key features include phase boundary lines, the triple point (where all three phases coexist), and the critical point (beyond which liquid and gas become indistinguishable).

Examples

  • Water's phase diagram showing ice, liquid water, and steam regions
  • The triple point of water at 0.01°C and 611.73 Pa
  • CO₂'s phase diagram explaining why dry ice sublimes at atmospheric pressure
Key Fact

Triple point: the unique temperature and pressure where solid, liquid, and gas coexist in equilibrium.

Related Terms

Phases of matter Colligative properties Water properties

Study This Concept

Practice phase diagrams with free review games in these units:

AP Chemistry Unit 3: Intermolecular Forces