A phase diagram is a graphical representation that shows the state (phase) of a substance (solid, liquid, or gas) under different conditions of temperature and pressure.
Key features of a phase diagram:
- Axes
- X-axis → Temperature
- Y-axis → Pressure
- Regions
- Solid region: Where the substance exists as a solid.
- Liquid region: Where it exists as a liquid.
- Gas region: Where it exists as a vapor/gas.
- Lines (boundaries)
- Fusion (melting/freezing) curve: Separates solid and liquid regions.
- Vaporization (boiling/condensation) curve: Separates liquid and gas regions.
- Sublimation curve: Separates solid and gas regions.
- Special points
- Triple point: The unique temperature and pressure where solid, liquid, and gas all coexist in equilibrium.
- Critical point: The temperature and pressure beyond which the liquid and gas phases cannot be distinguished (supercritical fluid).
Importance
- Helps to understand under what conditions a substance will exist as solid, liquid, or gas.
- Useful in chemistry, engineering, and material science.
In short: A phase diagram shows how the physical state of a substance changes with temperature and pressure, marking solid, liquid, gas regions, and special points like the triple point and critical point.