Triple Point

What is Triple Point?

The single, precise temperature and pressure at which a substance's solid, liquid and vapour phases all coexist simultaneously in equilibrium. Water's triple point is so exactly reproducible — at 0.01°C and a fixed pressure — that it was used for decades to formally define the kelvin.

The five clues

Engineerdle #52 described Triple Point with five clues, revealed one at a time from hardest to most direct. Each clue points at a different property of the concept.

1. 01A single, very specific combination of conditions on a phase diagram.
2. 02Solid, liquid and gas coexist there simultaneously, in equilibrium.
3. 03Water's version sits at a famously precise 0.01°C.
4. 04It's so reproducible that it once anchored the definition of the kelvin.
5. 05The unique temperature and pressure at which three phases of a substance coexist in equilibrium.

More Thermodynamics concepts

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