Triple Points

By Wednesday, January 12, 2011 , , , , 0


I saw an excellent TV programme last night on the BBC iPlayer.

The series was ‘Horizon’ and the episode was titled ‘What is one degree?’  (Click here to watch it).

The comedian Ben Miller presented the show (incidentally, he has a physics PhD from Cambridge University!) The programme mainly deals with temperature but there are a few sections that relate to chemistry.

What caught my eye in particular was a section on the triple point of water.

The triple point of a substance is when all three states (phases) occur simultaneously. The triple point of a substance is unique to the substance and will only occur at a certain temperature and pressure.

The triple point of water occurs at exactly 273.16 K (0.01 °C) and a pressure of 611.73  (0.0060373057 atm) and it has been used to define the Kelvin.

Matthieumarechal [GFDL ( or CC-BY-SA-3.0 (], via Wikimedia Commons

If you are able to watch the programme, I would thoroughly recommend it. You can read more on triple points starting here.

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