Under the right conditions, water can boil and freeze at the same time.
At a temperature of 0.01 degrees Celsius and a pressure of about six thousandths of normal air pressure, water reaches its triple point. Ice, liquid water and steam all exist together in equilibrium.
Why is this true?
Boiling and freezing depend on pressure as well as temperature. The triple point is so precisely defined that it was used for decades as the official reference for the Kelvin temperature scale.
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