Rucete ✏ Chemistry In a Nutshell
1. What is a Phase Diagram?
- A graph showing phase changes of a substance under different temperature and pressure conditions.
- Divides matter into solid, liquid, and gas regions.
- Helps predict phase transitions (melting, boiling, sublimation, etc.).
2. Key Points in a Phase Diagram
- Triple Point:
- The unique temperature and pressure where solid, liquid, and gas coexist in equilibrium.
- Example for water: 0.01°C, 0.006 atm.
- Critical Point:
- The highest temperature and pressure where a liquid can exist.
- Beyond this point, the substance becomes a supercritical fluid (no distinct liquid or gas phase).
- Phase Boundaries:
- Lines separating solid, liquid, and gas regions.
- Along these lines, two phases exist in equilibrium (e.g., liquid ⇌ gas at boiling point).
3. Water’s Unique Phase Diagram
Image source: By Caroline Monahan
- Unusual Slope of Solid-Liquid Line:
- Water’s melting curve has a negative slope, meaning ice melts at lower temperatures under high pressure.
- This happens because ice is less dense than liquid water (unlike most substances).
4. Interpreting a Phase Diagram
- Moving Right (Increasing Temperature):
- Solid → Liquid (Melting)
- Liquid → Gas (Boiling)
- Moving Up (Increasing Pressure):
- Gas → Liquid (Condensation)
- Liquid → Solid (Freezing)
In a Nutshell
- Triple Point = All Phases Coexist.
- Critical Point = No More Liquid, Just Supercritical Fluid.
- Phase Boundaries = Two Phases in Equilibrium.
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Chemistry in a nutshell