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Water: freezing and melting ( or solidification and fusion )
about freezing and melting temperature
Freezing of pure water
We can cause
the freezing of the pure water by immersing it in a refrigerant mixture
having a temperature below 0 ° C. Temperature measurements then
show that during solidification, pure water keeps a constant
temperature of 0 ° C.
The solidification of pure water always occurs at a constant
temperature of 0
of salt water
the freezing of a salt
it can be observed that its temperature: regularly decreases below
until it is completely frozen.
More generally, during the freezing
of a mixture, its temperature keeps on decreasing below the freezing
temperature of the pure substance.
This conclusion is also true for the vaporization, melting,
liquefaction, sublimation or deposition of a mixture.
Furthermore, measuring the freezing point of a substance is a method
used to check its purity ( this method is called cryoscopy )
Photo: Liquid salt water and ice can coexist at negative temperatures
because salt water freeze below 0°C
Photo courtesy of National
Oceanic and Atmospheric Administration/Department of Commerce
of pure water
of temperature in melting ice, would show that pure water keeps a
temperature of 0°C.
The melting of pure water always occurs at a constant temperature of
The melting temperature of pure water is therefore the same as its
freezing temperature and it is also true for all other pure substances:
melting and freezing occur at the same temperature.
another substance: cyclohexane
is a pure substance whose fusion can be compared to that of pure water.
Its melting occurs at a constant temperature, like pure water, but at 6
° C while the pure water has a melting temperature of 0
A pure substance changes state at a constant temperature that is
characteristic of this substance.
Particularly a melting or freezing at the constant temperature of
0°C is a characteristic that allows to identify pure water.
- Salt and the freezing point of water:
This article explains why freezing point of salt water is below
0°C and describes molecules of water in this solution.
- Freezing and melting: notes about
temperature, energy exchanges and molecules during freezing and melting
of various substances.
- The effect of dissolved Salt and sugar on
the melting rate of ice: Projet de sciences par un
a fait un travail
très sérieux afin
de comparer les effets du
sucre et du sel sur la
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