WATER

Water

From Wikipedia, the free encyclopedia

This article is about the chemical substance. For its chemical and physical properties, see water (molecule). For other uses, see Water (disambiguation).

Water in three states: liquid, solid (ice), and (invisible) vapor in air. Clouds are 

droplets of liquid, condensed from water vapor.

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. About 1.460 petatonnes (Pt) (1021kilograms) of water covers 71% of the Earth's surface, mostly in oceans and other large water bodies, with 1.6% of water below ground in aquifers and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles 

suspended in air), and precipitation.^[1] Saltwater oceans hold 97% of surface water, glaciers and polar ice caps 2.4%, and other land surface water such as rivers, lakes and 

ponds 0.6%.

A very small amount of the Earth's water is contained within water towers, biological bodies, manufactured products, and food stores. Other water is trapped in ice caps, 

glaciers, aquifers, or in lakes, sometimes providing fresh water for life on land.

Water moves continually through a cycle of evaporation or transpiration (evapotranspiration), precipitation, and runoff, usually reaching the sea. Winds carry water vapor over land at the same rate as runoff into the sea, about 36 Tt (1012kilograms) per year. Over land, evaporation and transpiration contribute another 71 Tt per year to the 

precipitation of 107 Tt per year over land. Clean, fresh drinking water is essential to human and other life. However, in many parts of the world—especially developing countries—there is a water crisis, and it is estimated that by 2025 more than half of the world population will be facing water-based vulnerability.^[2] Water plays an important role in the world economy, as it functions as a solvent for a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70% of freshwater is consumed by agriculture.^[3]

Types of water

Liquid water in motion

Water can appear in three states; it is one of the very few substances to be found 

naturally in all three states on earth. Water takes many different forms on Earth: water vapor and clouds in the sky; seawater and rarely icebergs in the ocean; glaciers and rivers in the mountains; and the liquid in aquifers in the ground.

Water can dissolve many different substances, giving it different tastes and odors. In fact, humans and other animals have developed senses which are, to a degree, able 

to evaluate the potability of water, avoiding water that is too salty or putrid. Humans also tend to prefer cold water to lukewarm; cold water is likely to contain fewer microbes. The taste advertised in spring water or mineral water derives from the minerals dissolved in it, as pure H₂O is tasteless. As such, purity in spring and mineral water refers to purity from toxins, pollutants, and microbes.

Different names are given to water's various forms:

Snowflakes by Wilson Bentley, 1902

according to state 

solid - ice

liquid - water

gaseous - water vapor

according to meteorology: 

hydrometeor 

precipitation

precipitation according to moves		precipitation according to state
vertical (falling) precipitation rain freezing rain drizzle freezing drizzle snow snow pellets snow grains ice pellets frozen rain hail ice crystals horizontal (seated) precipitation dew hoarfrost atmospheric icing glaze ice		liquid precipitation rain freezing rain drizzle freezing drizzle dew solid precipitation snow snow pellets snow grains ice pellets frozen rain hail ice crystals hoarfrost atmospheric icing glaze ice mixed precipitation in temperatures around 0 °C

levitating particles 

clouds

fog

mist

ascending particles (drifted by wind) 

spindrift

stirred snow

according to occurrence 

groundwater

meltwater

meteoric water

connate water

fresh water

surface water

mineral water – contains much minerals

brackish water

dead water – strange phenomenon which can occur when a layer of fresh or brackish water rests on top of denser salt water, without the two layers mixing. It is dangerous for ship traveling.

seawater

brine

according to uses 

tap water

bottled water

drinking water or potable water – useful for everyday drinking, without fouling, it contains balanced minerals that are not harmful to health (see below)

purified water, laboratory-grade, analytical-grade or reagent-grade water – water 

which has been highly purified for specific uses in science or engineering. Often broadly 

classified as Type I, Type II, or Type III, this category of water includes, but is not limited to the following:

distilled water

double distilled water

deionized water

according to other features 

soft water – contains less minerals

hard water – from underground, contains more minerals

distilled water, double distilled water, deionized water - contains no minerals

Water of crystallization — water incorporated into crystalline structures

Hydrates — water bound into other chemical substances

heavy water – made from heavy atoms of hydrogen - deuterium. It is in nature in normal water in very low concentration. It was used in construction of first nuclear reactors.

tritiated water

according to microbiology 

drinking water

wastewater

stormwater or surface water

according to religion 

holy water

Chemical and physical properties

Main article: Water (molecule)   model of hydrogen bonds between molecules of water

Water
Water is a necessary solvent for all known life, and an abundant compound on the earth's surface.
Information and properties
Common name	water
IUPAC name	oxidane
Alternative names	aqua, dihydrogen monoxide, hydrogen hydroxide, (more)
Molecular formula	H2O
CAS number	7732-18-5
InChI	InChI=1/H2O/h1H2
Molar mass	18.0153 g/mol
Density and phase	0.998 g/cm³ (liquid at 20 °C, 1 atm) 0.917 g/cm³ (solid at 0 °C, 1 atm)
Melting point	0 °C (273.15 K) (32 °F)
Boiling point	99.974 °C (373.124 K) (211.95 °F)
Specific heat capacity	4.184 J/(g·K) (liquid at 20 °C) 74.539 J/ (mol·K) (liquid at 25 °C)
Supplementary data page
Disclaimer and references

Impact from a water drop causes an upward "rebound" jet surrounded by circular 

capillary waves.

Dew drops adhering to a spider web

capillary action of water compared to mercury

Water is the chemical substance with chemical formula H2O: one molecule of water 

has two hydrogen atoms covalently bonded to a single oxygen atom.

The major chemical and physical properties of water are:

Water is a tasteless, odorless liquid at ambient temperature and pressure. The color 

of water and ice is, intrinsically, a very light blue hue, although water appears colorless in small quantities. Ice also appears colorless, and water vapor is essentially invisible as a gas.^[4]

Water is transparent, and thus aquatic plants can live within the water because 

sunlight can reach them. Only strong UV light is slightly absorbed.

Since oxygen has a higher electronegativity than hydrogen, water is a polar molecule. The oxygen has a slight negative charge while the hydrogens have a slight positive 

charge giving the article a strong effective dipole moment. The interactions between the different dipoles of each molecule cause a net attraction force associated with water's high amount of surface tension.

Another very important force that causes the water molecules to stick to one another is the hydrogen bond.[5]

The boiling point of water (and all other liquids) is directly related to the barometric 

pressure. For example, on the top of Mt. Everest water boils at about 68 °C (154 °F), compared to 100 °C (212 °F) at sea level. Conversely, water deep in the ocean near geothermal vents can reach temperatures of hundreds of degrees and remain liquid.

Water has a high surface tension caused by the weak interactions, (Van Der Waals 

Force) between water molecules because it is polar. The apparent elasticity caused by surface tension drives the capillary waves.

Water also has high adhesion properties because of its polar nature.

Capillary action refers to the tendency of water to move up a narrow tube against the force of gravity. This property is relied upon by all vascular plants, such as trees.

Water is a very strong solvent, referred to as the universal solvent, dissolving many 

types of substances. Substances that will mix well and dissolve in water, e.g. salts, sugars, acids, alkalis, and some gases: especially oxygen, carbon dioxide (carbonation), are known as "hydrophilic" (water-loving) substances, while those that do not mix well with water (e.g. fats and oils), are known as "hydrophobic" (water-fearing) substances.

All the major components in cells (proteins, DNA and polysaccharides) are also 

dissolved in water.

Pure water has a low electrical conductivity, but this increases significantly upon 

solvation of a small amount of ionic material such as sodium chloride.

Water has the second highest specific heat capacity of any known chemical compound, after ammonia, as well as a high heat of vaporization (40.65 kJ mol−1), both of 

which are a result of the extensive hydrogen bonding between its molecules. These two unusual properties allow water to moderate Earth's climate by buffering large fluctuations in temperature.

The maximum density of water is at 3.98 °C (39.16 °F).[6] Water becomes even less 

dense upon freezing, expanding 9%. This causes an unusual phenomenon: ice floats upon water, and so water organisms can live inside a partly frozen pond because the water on the bottom has a temperature of around 4 °C (39 °F).

ADR label for transporting goods dangerously reactive with water

Water is miscible with many liquids, for example ethanol, in all proportions, forming a single homogeneous liquid. On the other hand, water and most oils are immiscible 

usually forming layers according to increasing density from the top. As a gas, water vapor is completely miscible with air.

Water forms an azeotrope with many other solvents.

Water can be split by electrolysis into hydrogen and oxygen.

As an oxide of hydrogen, water is formed when hydrogen or hydrogen-containing 

compounds burn or react with oxygen or oxygen-containing compounds. Water is not a fuel, it is an end-product of the combustion of hydrogen. The energy required to split water into hydrogen and oxygen by electrolysis or any other means is greater than the energy released when the hydrogen and oxygen recombine.^[7]

Elements which are more electropositive than hydrogen such as lithium, sodium, 

calcium, potassium and caesium displace hydrogen from water, forming hydroxides. Being a flammable gas, the hydrogen given off is dangerous and the reaction of water with the more electropositive of these elements is violently explosive.

Distribution of water in nature

Water in the Universe

Much of the universe's water may be produced as a byproduct of star formation. When stars are born, their birth is accompanied by a strong outward wind of gas and dust. When this outflow of material eventually impacts the surrounding gas, the shock 

waves that are created compress and heat the gas. The water observed is quickly produced in this warm dense gas.^[8]

Water has been detected in interstellar clouds within our galaxy, the Milky Way. It is 

believed^[who?] that water exists in abundance in other galaxies too, because its components, hydrogen and oxygen, are among the most abundant elements in the universe. Interstellar clouds eventually condense into solar nebulae and solar systems, such as ours.

Water vapor is present on:

Mercury - 3.4% in the atmosphere, and large amounts of water in Mercury's exosphere[9]

Venus - 0.002% in the atmosphere

Earth - trace in the atmosphere (varies with climate)

Mars - 0.03% in the atmosphere

Jupiter - 0.0004% in the atmosphere

Saturn - in ices only

Enceladus (moon of Saturn) - 91% in the atmosphere

exoplanets known as HD 189733 b[10] and HD 209458 b.[11]

Liquid water is present on:

Earth - 71% of surface

Moon - small amounts of water have been found (in 2008) in the inside of volcanic 

pearls brought from Moon to Earth by the Apollo 15 crew in 1971.^[12]

Strong evidence suggests that liquid water is present just under the surface of Saturn's moon Enceladus. Probably some liquid water is on Europa.

Water ice is present on:

Earth - mainly on ice sheets

polar ice caps on Mars

Titan

Europa

Enceladus

Probability or possibility of distribution of water ice is at: lunar ice on the Moon, Ceres (dwarf planet), Tethys (moon). Ice is probably in internal structure of Uranus, Neptune, and Pluto and on comets.

Water and habitable zone

The Solar System along center row range of possible habitable zones of varying size stars.

The existence of liquid water, and to a lesser extent its gaseous and solid forms, on 

Earth is vital to the existence of life on Earth as we know it. The Earth is located in the habitable zone of the solar system; if it were slightly closer to or further from the Sun (about 5%, or about 8 million kilometres), the conditions which allow the three forms to be present simultaneously would be far less likely to exist.^[13]

Earth's mass allows gravity to hold an atmosphere. Water vapor and carbon dioxide 

in the atmosphere provide a greenhouse effect which helps maintain a relatively steady surface temperature. If Earth were smaller, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in polar ice caps (as on Mars).

It has been proposed that life itself may maintain the conditions that have allowed its continued existence. The surface temperature of Earth has been relatively constant 

through geologic time despite varying levels of incoming solar radiation (insolation), indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.

The state of water also depends on a planet's gravity. If a planet is sufficiently 

massive, the water on it may be solid even at high temperatures, because of the high pressure caused by gravity.

There are various theories about origin of water on Earth. From Wikipedia, the free encyclopedia

Penulis : Drs.Simon Arnold Julian Jacob