Amazing science April 26, 2020-triple point
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Started by metmike - April 25, 2020, 11:55 p.m.

Water can boil and freeze at the same time 



Seriously, it's called the 'triple point', and it occurs when the temperature and pressure is just right for the three phases (gas, liquid, and solid) of a substance to coexist in thermodynamic equilibrium.

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By metmike - April 25, 2020, 11:58 p.m.
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https://en.wikipedia.org/wiki/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.[1] It is that temperature and pressure at which the sublimation curve, fusion curve and the vaporisation curve meet. For example, the triple point of mercury occurs at a temperature of −38.83440 °C (−37.90192 °F) and a pressure of 0.2 mPa.

In addition to the triple point for solid, liquid, and gas phases, a triple point may involve more than one solid phase, for substances with multiple polymorphs. Helium-4 is a special case that presents a triple point involving two different fluid phases (lambda point).[1]

The triple point of water was used to define the kelvin, the base unit of thermodynamic temperature in the International System of Units (SI).[2] The value of the triple point of water was fixed by definition, rather than measured, but that changed with the 2019 redefinition of SI base units. The triple points of several substances are used to define points in the ITS-90 international temperature scale, ranging from the triple point of hydrogen (13.8033 K) to the triple point of water (273.16 K, 0.01 °C, or 32.018 °F).

The term "triple point" was coined in 1873 by James Thomson, brother of Lord Kelvin.[3]


 

A typical phase diagram. The solid green line applies to most substances; the dashed green line gives the anomalous behavior of water

The single combination of pressure and temperature at which liquid water, solid ice, and water vapor can coexist in a stable equilibrium occurs at approximately 273.1575 K (0.0075 °C; 32.0135 °F) and a partial vapor pressure of 611.657 pascals (6.11657 mbar;