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A solid, liquid, & gas at the same time: The Triple Point

How can a chemical be a solid, a liquid, and a gas at the same time? In the video above, a clear liquid called cyclohexane is experiencing the perfect pressure and temperature combination for its solid, liquid, and gas phases to co-exist within a repeating cycle. It’s called the triple point:

In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.

Sujata Kundu, Alistair Linsell, and Helen Arney explain the details in this clip from The Science Channel’s Outrageous Acts of Science. You can also find this handy Table of Triple Points on Wikipedia.

There’s more freezing, boiling, and pressure to watch in the archives. Try this one: Kari Byron makes a cloud in a bottle.

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