Water
chemical compound whose molecules are formed by two hydrogen atoms and one oxygen atom From Wikipedia, the free encyclopedia
Water (H
2O) is a simple chemical compound. It is made of two hydrogen atoms and one oxygen atom. It is clear, has no taste or smell, and is almost colorless. Water can be found in Earth’s rivers, lakes, and oceans. It is also found in all living things. All life needs water to survive, even though it doesn’t give energy or nutrients.[17] At normal temperatures and pressure, H₂O is called water in its liquid form. Water is called a universal solvent because it can dissolve many different substances.[18][19][20]
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| Names | |||
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| IUPAC name
water, oxidane | |||
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| Identifiers | |||
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3D model (JSmol) |
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| Beilstein Reference | 3587155 | ||
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| ChEMBL | |||
| ChemSpider | |||
| ECHA InfoCard | 100.028.902 | ||
| Gmelin Reference | 117 | ||
PubChem CID |
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CompTox Dashboard (EPA) |
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SMILES
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| Properties | |||
| H 2O | |||
| Molar mass | 18.01528(33) g/mol | ||
| Appearance | White crystal-like solid, almost colorless liquid with a hint of blue, colorless gas | ||
| Odor | None | ||
| Density | Liquid:[3] 0.9998396 g/mL at 0 °C 0.9970474 g/mL at 25 °C 0.961893 g/mL at 95 °C Solid:[4] 0.9167 g/ml at 0 °C | ||
| Melting point | 0.00 °C (32.00 °F; 273.15 K) [a] | ||
| Boiling point | 99.98 °C (211.96 °F; 373.13 K) [5][a] | ||
| N/A | |||
| Solubility | Poorly soluble in haloalkanes, aliphatic and aromatic hydrocarbons, ethers.[6] Improved solubility in carboxylates, alcohols, ketones, amines. Miscible with methanol, ethanol, propanol, isopropanol, acetone, glycerol, 1,4-dioxane, tetrahydrofuran, sulfolane, acetaldehyde, dimethylformamide, dimethoxyethane, dimethyl sulfoxide, acetonitrile. Partially miscible with Diethyl ether, Methyl Ethyl Ketone, Dichloromethane, Ethyl Acetate, Bromine. | ||
| Vapor pressure | 3.1690 kilopascals or 0.031276 atm[7] | ||
| Acidity (pKa) | 13.995[8][9][b] | ||
| Basicity (pKb) | 13.995 | ||
| Conjugate acid | Hydronium | ||
| Conjugate base | Hydroxide | ||
| Thermal conductivity | 0.6065 W/(m·K)[12] | ||
Refractive index (nD) |
1.3330 (20 °C)[13] | ||
| Viscosity | 0.890 cP[14] | ||
| Structure | |||
| Hexagonal | |||
| C2v | |||
| Bent | |||
| 1.8546 D[15] | |||
| Thermochemistry | |||
| Std enthalpy of formation ΔfH |
−285.83 ± 0.04 kJ/mol[6][16] | ||
| Standard molar entropy S |
69.95 ± 0.03 J/(mol·K)[16] | ||
| Specific heat capacity, C | 75.385 ± 0.05 J/(mol·K)[16] | ||
| Hazards | |||
| Main hazards | Drowning Avalanche (as snow)
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| NFPA 704 |
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| Flash point | Non-flammable | ||
| Related compounds | |||
| Other cations | {{{value}}} | ||
| Related {{{label}}} | {{{value}}} | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |||
| verify (what is ?) | |||
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Earth is just right for water to exist as: solid (ice), liquid (water), and gas (water vapor).[21] Water falls as rain or snow. It forms clouds and fog. It also moves through the air as vapor. About 71% of the Earth’s surface is covered by water. Most of it (around 96.5%) is in the oceans.[22] Smaller amounts of water are found underground in aquifers, in glaciers and ice caps in Antarctica and Greenland, and in the air as clouds and vapor. Water is always moving through the water cycle. It includes evaporation, condensation, precipitation, and runoff, often finding its way back to the ocean.[23][24]
Water is very important to the world economy. About 70% of the fresh water people use goes to farming.[25] Fish from oceans, lakes, and rivers is a very important source of food source.[26] A lot of goods, like crude oil and products, are moved around the world in ships using oceans, rivers, and canals.[27] Water is also used to heat and cool buildings and machines. Because water can dissolve many things, it is very useful in factories, cooking, and cleaning. Water is also a big part of sports and fun activities like swimming, boating, fishing, diving, ice skating, snowboarding, and skiing.
History
On Earth
The origin of water on Earth is a mystery scientists are still trying to solve. When trying to find out when water appeared on Earth, scientists have to consider the fact that water is being lost to space. In the atmosphere, sunlight breaks water (H₂O) into hydrogen and oxygen. The light hydrogen atoms can escape Earth's gravity into space. When Earth was younger and had weaker gravity, more water would have escaped. Light gases like hydrogen and helium still slowly escape into space today.[28] Normally, only light gases like hydrogen and helium slowly escape from Earth’s atmosphere into space. But when scientists look at heavier gases, they saw that they also escaped into space in the past.[29] Scientists can tell that Earth lost a huge amount of water. About as much as all the water in today’s oceans escaped into space early in Earth’s history. This might have been during major events like the impact that formed the Moon.[30]
The Moon formed about 4.5 billion years ago, when a huge object hit Earth. This might have turned most of Earth's surface into gas. It created a hot atmosphere filled with rocks in gas form. This rock gas quickly cooled and condensed back into solid rock within about 2,000 years.[31][32] This left behind, mainly carbon dioxide, along with hydrogen and water vapor in the atmosphere. Even though the surface was very hot (about 230 °C or 446 °F), the thick CO₂ atmosphere created high pressures that might have allowed oceans to form.[33] As Earth continued to cool, a lot of the carbon dioxide left the air by dissolving in the oceans and getting buried underground.[34]
Scientists use ancient rocks to figure out when water first appeared on Earth. One kind of rock they use is called pillow basalt, which forms when a volcano erupts underwater. One of these rock was found in the Isua Greenstone Belt and is about 3.8 billion years old. This tells us that there was liquid water on Earth at that time.[35] More of these very old rocks can be found in Canada, in a place called the Nuvvuagittuq Greenstone Belt. Some studies of these rocks also say there was water about 3.8 billion years old. Other studies suggest there was water 4.28 billion years.[36] If there was water, like oceans, even earlier than that, we don’t know yet. That might be because the Earth’s surface is always changing over time. Old rocks can be destroyed or buried through processes like plate tectonics and recycling of the crust, which can erase early signs of water. In 2020, scientists suggested that there might have been enough water to fill the oceans immediately after Earth formed.[37][38][39]
To understand what Earth was like after it formed, scientists study rocks called zircons. Unlike most rocks, zircons are very tough. They can survive for billions of years, making them useful for studying early Earth. Zircons show that there was liquid water and an atmosphere 4.404 billion years ago, not long after Earth formed.[40][41][42][43] This creates a problem, because the cool early Earth hypothesis says that Earth was cold enough to freeze water between 4.4 and 4.0 billion years ago.[44] Other zircon studies from ancient Australian rocks suggest that plate tectonics may have started around 4 billion years ago.[45] If that's true, Earth may have been similar to today, instead of being hot and covered in carbon dioxide. Plate tectonics helps trap carbon dioxide, which cools the planet and allows solid rock and liquid water to form.[46]
Properties of water
Water is a chemical substance. It is made up of two hydrogen atoms and one oxygen atom. They are connected by a covalent bond. At room temperature and normal pressure, water is a colorless, tasteless, and odorless liquid. It is called a "universal solvent" because it can dissolve more substances than any other liquid. But it cannot dissolve nonpolar substances like oil well. Water is also the only common material on Earth that can naturally be found as a solid, liquid, and gas. Water is also a very strange substance.
Even though it looks clear, water is actually a little blue. This is because it absorbs more light on the red part of the visible spectrum leaving blue light. You can see this blue color when looking at large amounts of water, such as in a white bathtub, swimming pool, or the ocean.[47]
Water, ice, and vapor
Water can be in solid, liquid, or gas. This depends on the temperature and pressure. They are called phases or states.
When we say "water" in everyday life, we're usually talking about liquid water. The form that flows from taps, fills oceans, rivers, and lakes, and is used for drinking, washing, and cooking. This is the most common form of water at the Earth's surface. When water gets cold enough, it freezes into a solid, which we call ice. This can look like hard cubes (like in a freezer) or soft, loose crystals such as snow. Ice usually forms in a hexagonal crystal structure. But there are other less common forms of ice. These are often found in extreme environments like outer space or deep inside ocean planets. When water heats up, it turns into water vapor, a gas. This is what we see as steam rising from boiling water or as clouds, which are made of tiny water droplets.
There's also another, less common form water can take, a supercritical fluid. This happens when water is heated to extremely high temperatures above 647 K (374°C or 705°F) and also placed under very high pressure (above 22.064 megapascals). Here, water acts like both a gas and a liquid at the same time. It can flow like a liquid but also fill a container like a gas. This strange state of water doesn’t happen naturally on Earth’s surface. But it can happen deep in the ocean. One example is near hydrothermal vents. This happens at depths of around 2200 meters. The ocean is much deeper on average at about 3800 meters.
Physical chemistry of water
Water is a fluid. Water is the only chemical substance on Earth that exists naturally in three states. There are over 40 anomalies (strange things) about water.[48] Unlike most other liquids such as alcohol or oil, when water freezes, it expands by about 9%.[49][50][51] This expansion can cause pipes to break if the water inside them freezes.
Water is a molecule made of two hydrogen atoms and one oxygen atom. Its chemical formula is H2O. Like other liquids, water has a surface tension, so a little water can make drops on a surface, rather than always spreading out to wet the surface.[52]
Things having something to do with water may have "hydro" or "aqua" in their name, such as hydropower or aquarium, from the Greek and Latin names for water. It is also called the "universal solvent", because it dissolves many other compounds.
In small amounts, water appears to have no color but in large amounts (such as seas or lakes), it has a very light blue color.
Uses of water
Plants and animals (including people) are mostly water inside, and must drink water to live. It gives a medium for chemical reactions to take place, and is the main part of blood. It keeps the body temperature the same by sweating from the skin. Water helps blood carry nutrients from the stomach to all parts of the body to keep the body alive. Water also helps the blood carry oxygen from the lungs to the body. Saliva, which helps animals and people digest food, is mostly water. Water helps make urine. Urine helps remove bad chemicals from the body. The human body is between 60% and 70% water, but this value differs with age; i.e. a foetus is 95% water inside.
Water is the main component of drinks like milk, juice, and wine. Each type of drink also has other things that add flavor or nutrients, things like sugar, fruit, and sometimes alcohol. Water that a person can drink is called "potable water" (or "drinking water"). The water in oceans is salt water, but lakes and rivers usually have unsalted water. Only about 3% of all the water on earth is fresh water. The rest is salt water.[53][54]
Many places, including cities and deserts, don't have as much water as people want. They build aqueducts to bring water there.
Though people can survive a few months without food, they can only survive for a day or two without water. A few desert animals can get enough water from their food, but the others must drink. Water has no smell, taste, or color.
Water is also used for recreational purposes, see list of water sports.
Water is used as both the coolant and the neutron moderator in most nuclear reactors. This may be ordinary water (called light water in the nuclear industry) or heavy water.
Water is also used for washing a lot of objects. Goods, services and people are transported to other countries in watercrafts on bodies of water.
Water is used in chemical reactions as a solvent or reactant. Water is also used in fire fighting. Water is also used for cooking.
Dihydrogen monoxide parody
The dihydrogen monoxide parody involves calling water by the unfamiliar chemical name "dihydrogen monoxide" (DHMO) and listing some of its harmful effects in an alarming way. Some examples include talking about how "it causes burning, suffocation and corrosion," when it is actually just talking about hot water, drowning and rust. Sometimes the parody calls for it to be banned and/or labelled as dangerous.
The prank works because it takes advantage of people's misunderstanding. Calling water by an unfamiliar name and making it sound like a harmful chemical can make people think it is dangerous.
"Dihydrogen monoxide" is an alternative chemical name for water, but nobody uses it. The word "dihydrogen" means two hydrogens, and "monoxide" means one oxygen. The chemical formula of water has two hydrogen atoms and one oxygen atom.
The parody gained most of its popularity in the 1990s, when a 14-year-old named Nathan Zohner collected anti-DHMO petitions for a science project about gullibility. Zohner fooled a lot of people, which has led to his project being used in lessons about critical thinking and the scientific method.
The website DHMO.org is a joke website which lists the harmful effects of water (DHMO), answers questions, and calls for it to be banned, among other things.
Origin of the Earth's water
The weirdness of water
A BBC short item explains that every molecule on Earth has existed for billions of years, and all of them came from elsewhere. Water is alien because it arrived on asteroids and comets. It is the second most common molecule in the universe. It is made of two very light elements. Ice floating on water is also an oddity, caused by the nature of water to expand and drop in density when it freezes. Also, hot water can freeze faster than cold, and both this effect and it's causes are still the source of scientific debate and study today. Molecules of water can move up against the force of gravity (that is due to surface adhesion).[55]
Water in the universe
Much of the universe's water is produced as a by-product of star formation.[57] On 22 July 2011, a report described the discovery of a gigantic cloud of water vapor containing "140 trillion times more water than the Earth's oceans combined" around a quasar 12 billion light years from Earth. According to the researchers, the "discovery shows that water has been prevalent in the universe for nearly its entire existence".[58][59]
Water has been detected in interstellar clouds in our galaxy, the Milky Way.[60] Water probably exists in abundance in other galaxies, too. Its components, hydrogen and oxygen, are among the most abundant elements in the universe. Most other planetary systems may have similar ingredients.
Origin of water on Earth: possibilities
We are not exactly certian how the Earth came to have so much water. It is everywhere in the Universe, but it is uncommon for a place to have so much. The reasoning is like this: every element (except hydrogen and some helium) has been formed in stars. Therefore, oxygen was originally formed in stars. The formation of water is not a problem: it is exothermic, so forming the molecule from its atoms does not need outside energy. But to explain why the Earth has so much compared to, for example, Mars, is not easy. It is an undecided problem in planetary geology.
For a while, people thought Earth’s water did not come from the planet’s region of the protoplanetary disk. Instead, it was thought that water and other volatiles must have been delivered to Earth from the outer Solar System later in its history. But hydrogen inside the Earth did play some role in the formation of the ocean.[61] The two ideas may each be partly right. Water was delivered to Earth by impacts from icy planetesimals (asteroids) in the outer edges of the asteroid belt.[62] How much is not known.
Water vapor
Water vapor (or water vapour) is the gas form of water. It is found in:
- Atmosphere of the Sun: this has tiny amounts of water.[63]
- Atmosphere of Mercury: it is composed of 3.4% of water. Mercury (planet) has large amounts of water in its exosphere.[64]
- Atmosphere of Venus: It is composed of 0.002% of water.[65]
- Atmosphere of Earth: It is composed of 0.4% of water all over the atmosphere. There is usually around 1–4% of water at the surface of the Earth. Water vapor is also found in the extremely thin atmosphere of the Moon in small amounts.[66]
- Atmosphere of Mars: It is composed of 0.03% of water.[67]
- Atmosphere of Ceres.[68]
- Atmosphere of Jupiter: It is composed of 0.0004% ice.[69] There is also water in its moon Europa.[70]
- Atmosphere of Saturn: It is has water in the form of ice. Enceladus is composed of 91% of ice and ice is also in Dione's exosphere.[71]
- Atmosphere of Uranus: Ice is found in small amounts.
- Atmosphere of Neptune: Ice is also found deep in the atmosphere of Neptune.[72]
- The atmosphere of extrasolar planets such as HD 189733 b and HD 209458 b, Tau Boötis b, HAT-P-11b, XO-1b, WASP-12b, WASP-17b, and WASP-19b.[73][74][29][75]
- Stellar atmospheres: Water vapor is found in giant hot stars such as Betelgeuse, Mu Cephei, Antares and Arcturus.[29]
Liquid water
Liquid water is found on Earth. It covers about 71% of the surface of the Earth. Liquid water is sometimes found in small amounts on Mars. Scientists believe that liquid water is in the moons Enceladus, Titan, Europa and Ganymede.[76][77][78][79][80]
Frozen water
The frozen form of water (ice) is found in:
- Mars: Water ice is found at the north and south poles of Mars.[81]
- Earth and the Moon: It is mainly found as ice sheets on Earth and in craters and volcanic rocks in the Moon.[82]
- Ceres.[83][84][85]
- Jupiter's moons: It is found on Europa, Ganymede and Callisto.[86][87][88]
- Saturn: It is found in the planetary rings of Saturn. It is also found in Titan and Enceladus.[89][90][91]
- Pluto and Charon.[89]
- Comets and other objects in the Kuiper belt and Oort cloud.[92]
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