WHAT ARE WATER ANOMALIES? - CHEMISTRY - 2024

The anomalies of water are those properties that distinguish and positioned as the most important and special all liquid substance. Physically and chemically, water shows a huge difference compared to other liquids, even exceeding expectations and theoretical calculations. Perhaps it is as simple, and at the same time as complex as life itself.

If carbon is the cornerstone of life, water corresponds to its fluid. If it were not unique and incomparable, a product of its anomalies, the carbon bonds that make up the biological matrices would be of no use; the perception of life would crumble, the oceans would freeze completely, and the clouds would not be suspended in the sky.

Icebergs and bodies of ice floating on the water represent a usually overlooked example of one of the water anomalies. Source: Pexels.

Water vapor is much lighter than other gases, and its interaction with the atmosphere results in the formation of clouds; the liquid is considerably more dense with respect to the gas, and this difference in its densities looks accentuated compared to other compounds; and the solid, anomalously, has a much lower density than the liquid.

An example of the latter is observed in the fact that icebergs and ice float in liquid water, a product of its lower density.

Specific heat

Beaches, another natural example where the anomalous specific heat of water is observed macroscopically. Source: Pixabay.

Water shows a severe opposition to increasing its temperature before a heat source. Therefore, the source must supply enough heat to force the water to raise its temperature by one degree centigrade; that is, its specific heat is high, higher than that of any ordinary compound, and has a value of 4.186 J / g · ºC.

Possible explanations for its anomalous specific heat are due to the fact that the water molecules form multiple hydrogen bonds, in a disorderly way, and the heat is dissipated to increase the vibrations of such bridges; otherwise, the water molecules would not vibrate at a higher frequency, which translates to an increase in temperature.

On the other hand, once the molecules have been thermally excited, they take time to re-establish the original state of their hydrogen bonds; this is the same as saying that it takes time to cool down under normal conditions, behaving as a heat reservoir.

Beaches, for example, display both behaviors during different seasons of the year. In winter they stay warmer than the surrounding air, and in summer cooler. For that reason it will be sunny, but when you swim in the sea it feels cooler.

Latent heat of vaporization

Water has a very high enthalpy or latent heat of evaporation (2257 kJ / kg). This anomaly synergizes with its specific heat: it behaves as a reservoir and regulator of heat.

Its molecules must absorb enough heat to pass into the gas phase, and the heat is obtained from their surroundings; especially on the surface to which they are attached.

This surface can be, for example, our skin. When the body exercises it releases sweat, whose composition is essentially water (greater than 90%). Sweat absorbs heat from the skin to vaporize, thus giving the sensation of cooling. The same happens with the soil, which after vaporizing its moisture, decreases its temperature and feels colder.

Dielectric constant

The water molecule is extremely polar. This is reflected in its dielectric constant (78.4 at 25ºC), which is higher than that of other liquid substances. Due to its high polarity, it is capable of dissolving a large number of ionic and polar compounds. It is for this reason that it is considered the universal solvent.

Diffusion

Diffusion of water through a pipe. Source: Pxhere.

One of the curious anomalies of liquid water is that it diffuses much faster than estimated through a hole that is reduced in size. Fluids generally increase their speed when they flow through narrower pipes or channels; but the water accelerates more drastically and violently.

Macroscopically this can be observed by varying the cross-sectional area of ​​the pipes through which the water circulates. And nanometrically, the same can be done but using carbon nanotubes, according to computational studies, which help to clarify the relationship between molecular structure and dynamics of water.

Density

It was mentioned at the beginning that ice has a lower density than water. In addition to this, it reaches a maximum value around 4ºC. When the water cooled below this temperature, the density begins to decrease and the colder water rises; and finally, close to 0ºC, the density falls to a minimum value, that of ice.

One of the main consequences of this is not just that icebergs can float; but also, it favors life. If the ice were more dense, it would sink and cool the depths to freezing. The seas would then cool from the bottom up, leaving only a film of water available for marine fauna.

In addition, when water seeps into the recesses of rocks, and the temperature drops, it expands when it freezes, promoting its erosion and external and internal morphology.

Light water and heavy water

As the ice floats, the surfaces of lakes and rivers freeze, while fish can continue to live in the depths, where oxygen dissolves well and the temperature is above or below 4ºC.

On the other hand, liquid water, in fact, is not considered ideally homogeneous, but consists of structural aggregates with different densities. At the surface, the lightest water is located, while at the bottom, the densest.

However, such liquid-liquid "transitions" are only noticeable in supercooled water and under simulations with high pressures.

Ice expansions

Another characteristic anomaly of water is that ice decreases its melting temperature as pressure increases; that is, at higher pressure, the ice melts at lower temperatures (below 0ºC). It is as if the ice, instead of contracting, expands as a result of pressure.

This behavior is contrary to that of other solids: the higher the pressure on them, and therefore, their contraction, they will require a higher temperature or heat to melt and thus be able to separate their molecules or ions.

It is also worth mentioning that ice is one of the most slippery solids in nature.

Surface tension

Insect walking on the surface of the water. Source: Pixabay.

Finally, although only a couple of anomalies have been mentioned (of the approximately 69 that are known and many others to be discovered), water has an abnormally high surface tension.

Many insects take advantage of this property to be able to walk on water (top image). This is because its weight does not exert enough force to break the surface tension of the water, whose molecules, instead of expanding, contract, preventing the area or surface from increasing.

References

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