How Does Pressure Affect The Crystallization Process Of Water?
October 25, 2021
Let’s try to link the dynamics of changes in the freezing point of water to a change in pressure.
At a pressure of 2 atm, water freezes at a temperature of -2 degrees.
At a pressure of 3 atm, the beginning of the freezing of water will be a temperature of -4 degrees Celsius.
At increased pressure, the temperature at the beginning of the water crystallization process decreases and the boiling point increases. At low pressure a diametrically opposite image is obtained.
That is why it is very difficult to cook eggs even at a high altitude and in a rarefied atmosphere, because the water in the pot is already boiling at 80 degrees. Obviously, it is simply impossible to cook food at this temperature.
At high pressure, the ice melting process under the skate blades takes place even at very low temperatures, but it is thanks to this that the skates slide on the ice surface.
The freezing of the runners of heavily loaded sleds in the stories of Jack London is explained in a similar way. Heavy sleds that put pressure on the snow cause it to melt. The resulting water makes them easier to slide. But as soon as the sleds stop and stay in one place for a long time, the displaced water, freezing, will freeze the runners to the road.
Crystallization Temperature Of Aqueous Solutions
Being an excellent solvent, water readily reacts with various organic and inorganic substances, forming a mass of sometimes unexpected chemical compounds. Of course, each of them will freeze at different temperatures. Let’s show this in a visual list.
The freezing point of a mixture of alcohol and water depends on the percentage of both components in it. The more water added to the solution, the closer to zero the freezing point. If there is more alcohol in the solution, the crystallization process starts at values close to -114 degrees.
It is important to know that water-alcohol solutions do not have a fixed freezing point. Usually they talk about the temperature of the beginning of the crystallization process and the temperature of the final transition to the solid state.
Between the beginning of the formation of the first crystals and the complete solidification of the alcohol solution, there is a temperature interval of 7 degrees. Thus, the freezing point of water with an alcohol concentration of 40% in the initial phase is -22.5 degrees, and the final transition of the solution to the solid phase will occur at -29.5 degrees.
The freezing point of water with salt is closely related to the degree of salinity: the more salt in the solution, the lower the position of the mercury column will freeze.
To measure the salinity of water, a special unit is used – “ppm”. So we have found that the freezing point of water decreases with increasing salt concentration. Let’s explain this with an example:
The salinity of ocean water is 35 ppm, with an average freeze of 1.9 degrees. The salinity of the waters of the Black Sea is 18-20 ppm, so they freeze at a higher temperature with a range of -0.9 to -1.1 degrees Celsius.