What is the triple point of water in Kelvin?

The triple point of water is the specific temperature and pressure at which its solid, liquid, and gas phases coexist in thermodynamic equilibrium. Historically, the kelvin was defined so that the triple point of water was set at exactly 273.16 K. Following the 2019 SI revision, the kelvin is now defined by fixing the Boltzmann constant, making the triple point of water an experimentally measured value rather than a fixed definition.

What we know

• The triple point of water occurs at 273.16 K. [2, 3]
• Before 2019, the triple point of water was used to define the kelvin as exactly 273.16 K. [2, 3]
• In the 2019 revision of the SI, the kelvin was redefined by fixing the Boltzmann constant, turning the triple point of water into an experimentally measured constant. [2, 3]
• The triple point temperature of 273.16 K is equivalent to 0.01 °C. [2, 3]

Where to go next

• the bigger pictureHow is thermodynamic temperature measured?
• whenWhat changed in the 2019 revision of the SI base units?
• how it workedWhat is the Boltzmann constant?
• a case in pointWhat are the triple points of other substances like hydrogen and mercury?
• whoWho was Lord Kelvin and how did he develop the temperature scale?
• an unexpected connectionHow is James Thomson connected to the term triple point?The term triple point was first coined on August 3, 1871, by James Thomson, who happened to be the brother of Lord Kelvin.

Sources

• [1]triple point (Wikidata Q106410) · CC0 1.0
• [2]Triple point · CC BY-SA 4.0
• [3]Kelvin · CC BY-SA 4.0
• [4]Water (data page) · CC BY-SA 4.0
• [5]Thermodynamic temperature · CC BY-SA 4.0

Your path

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