Table of Contents
Introduction:
At moderate temperatures, liquids expand when heated and contract when cooled. Water, on the other hand, behaves in an unusual manner. Consider 1 kg of water at 0 degrees Celsius. When heated from 0 degrees Celsius to 4 degrees Celsius it actually contracts rather than expands. At 4 degrees Celsius, the volume of water is at its smallest. Water begins to expand once it reaches 4 degrees Celsius. This behaviour of water between 0 and 4 degrees Celsius is known as anomalous expansion of water. Most liquids expand when heated and contract when cooled. Water, at a specific temperature range, appears to defy this theory.
Anomalous expansion of water is necessary for aquatic life to survive in cold regions or during the winter. When it is cold outside, the top layer of a body of water cools first. The top layer’s temperature drops to 4°C. The top layer then becomes denser than the lower layers and descends to the bottom of the body of water. This process is repeated indefinitely to produce a temperature gradient. The temperature in the lowest layer remains constant at 4°C. Aquatic life can thrive at 4°C. As the depth decreases, so does the temperature. The coldest layer is the topmost layer. Eventually, the top layer freezes, forming an insulating blanket that, to some extent, prevents further freezing. If there had been no anomalous expansion, the waterworks would have completely frozen.
Overview:
The Anomalous Expansion of Water is the increase in water volume when it is cooled from 4°C to 0°C (or 39.2°F to 32°F). Water is a necessary component of all living things on Earth. As a result, studying the nature of water is critical for any sane study of life and organisms. Water is a special molecule with some peculiar and one-of-a-kind properties. The Anomalous Thermal Expansion of Water in the Temperature Range of 0°C to 4°C is one such unusual phenomenon.
The graph below depicts a plot of water density versus temperature.
The density of water increases from 0°C to its maximum at 4°C. It decreases after 4°C, just like any other liquid with normal behaviour. Anomalous Expansion occurs between 0°C and 4°C. The density of water decreases as a result, and the volume of water increases.
Properties of Water:
Water molecules are highly polar and form hydrogen bonds with one another. Because of its polarity, it can dissociate ions in salts and bond to other polar substances like alcohols and acids, dissolving them. Because of its hydrogen bonding, it has many distinct properties, including a solid form that is less dense than its liquid form, a relatively high boiling point of 100 °C for its molar mass, and a high heat capacity.
Physical properties:
Water has the chemical formula H2O; one molecule of water contains two hydrogen atoms covalently bonded to a single oxygen atom. At room temperature and pressure, water is a tasteless and odourless liquid. Liquid water has weak absorption bands at wavelengths around 750 nm, giving it a blue appearance. This is easily visible in a white-lined water-filled bath or wash basin. Large ice crystals, such as those found in glaciers, appear blue as well.
Water is primarily a liquid under normal conditions, in contrast to other analogous hydrides in the oxygen family, which are generally gaseous. Hydrogen bonding is responsible for water’s one-of-a-kind property. At timeframes faster than 200 femtoseconds, water molecules are continually moving in respect to one another, and hydrogen bonds are constantly breaking and repairing. These bonds, however, are strong enough to produce many of water’s peculiar properties, some of which make it essential to life.
Water is a tasteless, colourless liquid. Water molecules have a lot of hydrogen bonding, which gives it strange qualities when it’s condensed. High melting and boiling points result as a result of this. Other liquids have lower specific heat, thermal conductivity, surface tension, dipole moment, and other properties than water. These characteristics account for its importance in the biosphere. Because water is a good solvent, it aids in the transfer of ions and molecules needed for metabolism. It has a high latent heat of evaporation, which aids in body temperature regulation.
Chemical properties:
Dissolved salts, micronutrients, metals, and gases are always present in natural waters. In fact, water dissolves so many substances that it is sometimes (mistakenly) referred to as the “Universal Solvent.” While the majority of these substances are necessary for healthy aquatic ecosystems, as concentrations rise, they can have negative effects and are referred to as pollutants.
Polarity: Water is made up of polar molecules, so polarity is one of its distinguishing characteristics. There are two hydrogen atoms and one oxygen atom in each water molecule (H2O). Polar covalent bonds are formed by these molecules. The hydrogen atoms have a positive charge, while the oxygen molecules have a negative charge. Water molecules are drawn to one another as a result of this property.
Cohesion: Water’s polarity contributes to its cohesion. The forces that cause or allow molecules to stick together are referred to as cohesion forces. Water has cohesion because water molecules naturally want to cling to one another. Water droplets can form as a result of this. Cohesion also explains why a container can be filled to just above the point of overflowing before spilling.
Surface tension: Water has the second-highest surface tension of any liquid (mercury is higher). Water molecules at the surface form stronger bonds than those below the surface because they want to cling together. As a result, surface tension develops, forming a barrier between the water and the air above it (the atmosphere). Surface tension explains why small objects float on top of the water rather than sink beneath it.
Viscosity: The higher the viscosity of a fluid, the more it resists flow. In contrast, the lower the viscosity of a liquid, the more freely it flows. A honey-like fluid is an example of a highly viscous fluid. Of course, water is not as viscous as honey, but it does have viscosity. The temperature has an effect on the viscosity of water. There is an inverse relationship, which means that as the water temperature rises, so does its viscosity.
Anomalous Expansion of Water:
When the temperature of the surrounding environment falls below 0 Degree Celsius, the temperature of the water on the surface of the lake or pond falls to 0 degrees Celsius as well, and it condenses into ice. Because ice is a poor conductor of heat, the ice on the surface prevents heat from passing from the water to the atmosphere. As a result, the water below the ice layer remains at 4 degrees Celsius. As a result, fish and other aquatic animals, as well as plants, can survive.
A common observation in the behaviour of substances is that they expand when heated as their density decreases, and the opposite occurs when the material is cooled. This is how most substances react to heat. Let’s take a look at how water reacts when heated. Until 4°C, the general tendency of cold water remains unchanged. Water’s density gradually increases as it cools. When the temperature reaches 4°C, the density reaches its maximum. What happens next will astound you. When you cool it further to make ice, i.e. 0°C, water expands with a further drop in temperature, implying that the density of water decreases when it is cooled from 4°C to 0°C. The graph below explains this behaviour.
As a result of this water expansion, the coldest water is always present on the surface. Because the water at 4°C is the heaviest, it settles at the bottom of the water body, while the lightest, i.e. the coldest layer, accumulates on top. As a result, in the winter, the top of the water is always the first to freeze. Because ice and water are both poor conductors of heat, this top layer of ice insulates the rest of the water body from the winter cold, protecting all life in the water body. You can now truly appreciate how important water’s anomalous properties are to life.
Frequently Asked Questions (FAQs):
Question 1: What is Anomalous Expansion of Water?
Answer: The Anomalous Expansion of Water is the increase in water volume when cooled from 4°C to 0°C (39.2 F to 32 F).
Question 2: How to prove anomalous expansion of water at home?
Answer: Fill a plastic bottle halfway with water. Close the bottle’s mouth with a cork. Place the bottle in the freezer to cool.
Question 3: When the temperature of the water drops, the cork comes out after some time. What are some other anomalous expanding liquids?
Answer: Gallium, silicon, germanium, and other elements exhibit anomalous expansion similar to water.
