The Mariana Trench is 10,000 meters deep. Is water at a depth of 10,000 meters still liquid? Water at a depth of 10,000 meters is naturally still liquid water, but there are also special states of water that can be said to lie between the liquid state and the gaseous state, that is to say that the temperature of water in the supercritical state can reach more than 400°C.
The pressure in the deep sea is very high, but liquid water is relatively stable in nature, and the pressure of water on the seafloor cannot destroy the arrangement of water molecules. liquid water, so the water in the deep sea remains liquid. Because sunlight cannot reach the depths of the sea, the temperature is very low, close to freezing. Due to friction between seawater and the seafloor, and heat transfer between deep seawater and surface seawater, deep sea water is close to but. cannot reach zero. Regardless of pressure or temperature, water at a depth of 10,000 meters is always liquid. However, the seabed environment is relatively complex. Although the overall temperature is relatively low, due to the activity of underwater volcanoes, the sea water temperature in some areas is very high. Since the seawater pressure is also very high, the seawater has become supercritical. State.
The point where the liquid and gas phases are in equilibrium is called the critical point. The temperature and pressure at the critical point are called critical temperature and critical pressure. The critical temperature and critical pressure of sea water are 374. °C and 21.7 MPa respectively, the seabed pressure at 10,000 meters exceeds the critical water pressure, and there are many cracks of plates on the seabed, which swallow upt a lot of sea water every year. However, the temperature and pressure inside the earth are different. very high, and the sea water will be heated and can easily exceed the critical temperature. Finally, it is extruded and ejected, so the sea water in the ocean will not be reduced because the land swallows it at the same time, because of the pressure. and the temperature of this water has reached the critical point, this water has become a supercritical state. Scientists have detected supercritical water at the highest temperature found in nature, reaching more than 400 degrees Celsius.
Supercritical water has high solubility and better compressibility, which is why power generation units will now use supercritical water to drive steam turbines to produce electricity. electricity. At the same time, supercritical water has very high solubility. extract many chemicals from insidee the earth, so that the chemical bacteria present on the seabed have sufficient nutrients and heat. Therefore, scientists believe that seabed hot springs could be the place of origin of life on earth.
The source of fresh water for water resources
This seems a silly question, because even children in the first grade of primary school know that water is 0, it will freeze at 0℃. Middle school textbooks clearly state that the freezing point of water is 0℃. Most scientific papers also set the freezing point of water at 0℃. Discussing this issue is simply troubleshooting. .
But is that really the case? Today we're going to talk about the science of freezing water.
Ice
The freezing point of water is actually much lower than 0℃
When we put a cup of tap water into the Drefrigerator, it will freeze into ice at 0℃ Block, this seems to confirm the manual's statement. But if you are a mysophobic person, if you wash the cup very clean, pour a cup of distilled water and put it in the refrigerator, you may notice a strange phenomenon: you will get a glass of water from the refrigerator. you took out was still a glass of water, but when you placed the glass on the table and inserted a straw into it, it froze.
If you have trouble washing cups, you can also put pure water bought from the supermarket directly into the freezer compartment of the refrigerator and achieve similar results. The prerequisite for the success of this experiment is that the water you put in the refrigerator must be pure or distilled water, not mineral water or natural water. At the same time, you need to be very gentle when taking the bottle out of the refrigerator. We will explain thisa below.
An experiment with supercooled water
If you are smart, you must have thought that this phenomenon is called “supercooled water”. In other words, the water you carefully remove from the refrigerator is actually below 0°C, but it will not turn into ice because certain conditions are not met.
Why does water freeze?
Water is a liquid at room temperature. It is made up of countless water molecules. Each water molecule has one oxygen atom and two hydrogen atoms. The outermost shell of the oxygen atom has two pairs of free electrons. It can easily obtain two electrons from the outside world. In this way, the oxygen combines with the two hydrogen atoms to form a water molecule shaped like. a Mickey Mouse head. Two hydrogen atoms are like Mickey Mouse's ears.
3D model of water molecule
Because the electrons of the atome of hydrogen are attracted to the oxygen atom side, the hydrogen atom side of the water molecule is positively charged, while the oxygen atom side is negatively charged , which makes water molecules polar, which is a key factor for water molecules to form hydrogen bonds.
Water molecules are polar
When many water molecules come together, the negatively charged oxygen atoms attract the positively charged hydrogen atoms of another water molecule, forming hydrogen bonds, so each water molecule can form hydrogen bonds with four surrounding water molecules. In fact, most of the physical and chemical properties of water are closely linked to these hydrogen bonds.
Water molecules are linked by hydrogen bonds
From the above analysis, we can see that water molecules are linked together by a attractionelectrostatic such as hydrogen bonds, because this force is relatively weak. each water molecule can swing in its own position, and it can also change position at any time, so water behaves like a viscous liquid flowing at room temperature.
As the temperature gradually decreases, the energy obtained by water molecules becomes smaller and smaller, and the amplitude of its shaking becomes smaller and smaller. When the electrostatic force of the hydrogen bond is dominant, the positions of. the water molecules will be fixed in relation to each other to form crystals. It's solid ice.
The arrangement of water molecules in ice crystals
Conditions of phase change of water
Water generally occurs in three forms: gas, liquid and solid (superfluid, etc. (ignored here), these three forms are also called the three phaits water. The phase change of water is affected by temperature and pressure, which is generally reflected in the phase change curve below.
The relationship between the phase change of water and temperature and pressure
In fact, when water is at an appropriate temperature, it does not immediately experience a phase change. Water condensation. requires another important factor, that is, it requires a condensation core. Known as the "nucleation effect", whether gaseous water condenses into liquid or liquid water freezes, water molecules alone are not enough. Impurities must also be involved, otherwise the temperature to complete the phase change will change significantly.
Most water in nature is rich in impurities, including tiny solid particles and mineral salts that we cannot see. Since these impurities havecharges different from those of water molecules, they are more likely to change their structure. state of surrounding water molecules. Studies have shown that if these impurity particles or molecules have more positive charges, it is easier for the water molecules around them to reduce vibration, because the impurity molecules are larger and the impurities are charged. positively will attract the oxygen atoms in the water molecules. It is forcibly attached, thereby causing other surrounding water molecules to nucleate and form crystals.
All snowflakes are ice crystals formed by the nucleation of water vapor in the air around dust and impurities
Pure water is difficult to nucleate and condense
Pure water is mainly distilled. Or it is manufactured by reverse osmosis technology. It contains very few impurities, so pure water lacks nucleate conditionsion. In reality, it is difficult to prepare ultrapure water, but scientists have concluded experimentally that ultrapure water nucleates uniformly only at -48.3°C under standard pressure. extremely small. Since there is no nucleation site, the hydrogen bonds between it and other surrounding water molecules are difficult to attach. At this point, the water is still supercooled liquid water.
Supercooled water is always in a critical state of crystallization. Once you put a condensation core into it, or even a small dust or ice crystal, it will crystallize at an extremely fast speed as the center and become a whole block of ice.
Another situation is where supercooled water vibrates, nucleates and freezes rapidly. When you stir it with a glass rod or lightly tap the cup, some water molecules in it will change angles due to vibration, resulting inwill be a change in distance from adjacent water molecules. This change will result in hydrogen bonds between molecules. Adjustment, resulting in rapid crystallization.
A bottle of supercooled water is shaken and crystallizes quickly
When conditions are right, the water freezes quickly
The temperature at high altitudes is often below -10°C, but there are still a lot of liquid water droplets and water vapor in the clouds, and they will not freeze due to the lack of solid dust and impurities. When a plane passes through these clouds, small supercooled water droplets quickly nucleate and form ice on the fuselage and wings, seriously affecting aviation safety. Therefore, pilots will avoid these clouds based on airborne radar or ground instructions.
Supercooled water in high altitude clouds freezing on the wings will affect safetyof theft.
When we take frozen food out of the refrigerator, it will be sticky on our hands. too excessive Cold temperatures quickly freeze the sweat on our fingers, freezing them along with the food. There is no need to worry because the heat from your finger can melt this thin layer of ice in seconds.
On the other hand, you should pay attention to this advice: in the cold northern winters, do not try to lick the outdoor iron pillars, the ice will quickly stick to your tongue and cause you problems you can't get rid of.
Surface water refers to freshwater rivers, lakes, or wetlands. Surface water accumulates from natural precipitation and snowfall over many years and is naturally lost to the ocean or through evaporation and infiltration into the ground.
Although the natural source of water for any water systemSurface water comes only from precipitation in the watershed, many other factors influence the total amount of water in the system. These factors include the storage capacity of lakes, wetlands and reservoirs, soil permeability and surface runoff characteristics in the watershed. Human activities have a significant impact on these properties. Humans build reservoirs to increase water storage and drain wetlands to reduce water storage. Human reclamation activities and ditch construction increase the volume and intensity of runoff.
The amount of water currently available must be taken into account. Some people's water needs are temporary. For example, many farms require large amounts of water in the spring but not at all in the winter. To provide water to these types of farms, water systems fromsurface require large volumes of water to collect water throughout the year and release it over short periods of time. Another part of the water demand is recurring, such as cooling water for power plants. In order to supply water and power plants, the surface water system needs a certain water storage capacity, and it can be replenished when the power plant does not have enough water .
Canada has the largest water reserve in the world. Groundwater is water stored in formation voids below the vadose zone, including rock pores, fissures and caves.
The water is divided into several underground layers and constitutes what is called the aquifer. Desalination is a process that transforms salt water (usually seawater) into fresh water. The most common methods are distillation and reverse osmosis. Today, desalinationement is more expensive than other methods and only provides enough fresh water to meet the needs of a very small number of people. This method is only of economic value for very economical use of water in dry desert areas. So far, it is most widely used in the Persian Gulf.
However, with the tracking of technology, the cost of seawater desalination is getting lower and lower, and solar seawater desalination technology is attracting more and more people. 'attention.
There have been several projects aimed at using icebergs as a source of fresh water, but so far they have been limited to new uses and have not yet been implemented with success. Runoff from glaciers is considered surface water.