Water has a special property that distinguishes it from almost all other liquids. It has its smallest volume and thus its greatest density at 4 °C. If we assume 4 °C, the volume increases with an increase in temperature as well as with a decrease in temperature. The density becomes smaller with it. This non-normal thermal behavior of water is known in physics as Anomaly of water denotes.
Properties of the water
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Change in the states of matter
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Class work – water and salts
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Water has a special property that sets it apart from almost all other liquids. At 4 °C it has its smallest volume and thus its greatest density . This abnormal thermal behavior of water is known in physics as the Anomaly of water denotes.
At temperatures above 4 °C water behaves like other liquids. When the temperature increases, it expands, when the temperature decreases, its volume decreases.
If water cools down below 4 °C, its volume increases again up to 0 °C. If the water then freezes, it expands further. While water of 0 °C has a density of about
the density of ice at 0 °C is as follows
Therefore ice floats on water. The ratio of the densities of ice and water is also the reason why about 9/10 of an iceberg is under water and only about 1/10 is above water.
Water has its smallest volume and greatest density at 4 °C
The density of water as a function of temperature
Precise measurements can be used to determine the dependence of the density of water on temperature. Figure 2 shows the values for the density of water at different temperatures.
Density of water as a function of temperature
Significance of the anomaly of the water
The anomaly of the water is very important for the life of animals and plants in the water and makes this life only possible. To do this, let’s consider the conditions in a lake at different times of the year.
At Summer the water is warmed by the sun. The lighter, warmer water remains on the surface and is mixed by wind in the upper layers. Deeper layers are cooler. A characteristic temperature stratification is formed. This temperature stratification of the water can be z. B. when bathing. The greater the depth, the lower the temperature of the water becomes.
Stable stratification of water in summer
In Autumn the solar radiation is lower. The air is also cooler. The water cools down gradually. Currents cause mixing of the water and thus also temperature equalization.
In Winter If it continues to cool, a stable state is reached again. A characteristic temperature stratification is formed again. The water with the greatest density, i.e. water of 4 °C, sinks downwards. With further cooling the temperature of the water near the surface decreases further. It eventually reaches 0 °C. The water starts to freeze. Since the density of ice is less than that of water, the ice floats to the top and forms a stable layer. If the water is sufficiently deep, there is a layer of water under the ice, which has a temperature of 4 °C at the bottom. Plants and animals living in water have adapted to these conditions and are able to survive.
Stable stratification of water in winter
At Spring the solar radiation increases again. There is a gradual warming, a mixing of the water and thus a temperature equalization.
spring circulation of the water
Water and ice as explosives
The expansion of water when it cools, and especially when it forms ice, must be considered in everyday life because freezing water acts like an explosive. Freezing z. B. If water enters freely lying water pipes or pumps and there is water in them, this water expands when ice forms and can damage the pipes or pumps. Pumps literally blast apart. Therefore, it is also necessary to give the cooling water of passenger cars Antifreeze The water must be added to the radiator, because otherwise there is a possibility that the coolant will freeze and burst the radiator.
In nature, the explosive effect of ice also plays an important role. How water penetrates rock crevices and cracks. It expands when it freezes. Chunks of stone are blown off rocks, larger stones are split. On rock faces this causes the formation of characteristic Debris cone From.
The blasting effect of the ice also loosens the soil, especially if it is plowed before frost.