H2o vatten människan
Grundvatten och färskvatten är användbara, eller potentiellt användbara, för människor som vattenresurser. Water is an inorganic compound with the chemical formula H 2 O. It is a transparent, tasteless, odorless, [ c ] and nearly colorless chemical substance. It is the main constituent of Earth 's hydrosphere and the fluids of all known living organisms in which it acts as a solvent [ 20 ].
It is vital for all known forms of life , despite not providing food energy or organic micronutrients. Its chemical formula, H 2 O , indicates that each of its molecules contains one oxygen and two hydrogen atoms , connected by covalent bonds. The hydrogen atoms are attached to the oxygen atom at an angle of Because Earth's environment is relatively close to water's triple point , water exists on Earth as a solid , a liquid , and a gas.
Clouds consist of suspended droplets of water and ice , its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or water vapor. Water plays an important role in the world economy. Large quantities of water, ice, and steam are used for cooling and heating in industry and homes.
Water is an excellent solvent for a wide variety of substances, both mineral and organic; as such, it is widely used in industrial processes and in cooking and washing. Water, ice, and snow are also central to many sports and other forms of entertainment, such as swimming , pleasure boating, boat racing , surfing , sport fishing , diving , ice skating , snowboarding , and skiing.
One factor in estimating when water appeared on Earth is that water is continually being lost to space. H 2 O molecules in the atmosphere are broken up by photolysis , and the resulting free hydrogen atoms can sometimes escape Earth's gravitational pull.
Hydrologia – vatten som vetenskap och konst
When the Earth was younger and less massive , water would have been lost to space more easily. Lighter elements like hydrogen and helium are expected to leak from the atmosphere continually, but isotopic ratios of heavier noble gases in the modern atmosphere suggest that even the heavier elements in the early atmosphere were subject to significant losses.
Not only is it a noble gas and therefore is not removed from the atmosphere through chemical reactions with other elements , but comparisons between the abundances of its nine stable isotopes in the modern atmosphere reveal that the Earth lost at least one ocean of water early in its history, between the Hadean and Archean eons. Any water on Earth during the latter part of its accretion would have been disrupted by the Moon-forming impact ~4.
Afterward, liquid water oceans may have existed despite the surface temperature of °C °F due to the increased atmospheric pressure of the CO 2 atmosphere. As the cooling continued, most CO 2 was removed from the atmosphere by subduction and dissolution in ocean water, but levels oscillated wildly as new surface and mantle cycles appeared. Geological evidence also helps constrain the time frame for liquid water existing on Earth.
A sample of pillow basalt a type of rock formed during an underwater eruption was recovered from the Isua Greenstone Belt and provides evidence that water existed on Earth 3. More recently, in August , researchers reported that sufficient water to fill the oceans may have always been on the Earth since the beginning of the planet's formation. Water H 2 O is a polar inorganic compound.
At room temperature it is a tasteless and odorless liquid , nearly colorless with a hint of blue. The simplest hydrogen chalcogenide , it is by far the most studied chemical compound and is sometimes described as the "universal solvent" for its ability to dissolve more substances than any other liquid, [ 45 ] [ 46 ] though it is poor at dissolving nonpolar substances.
Water is the only common substance to exist as a solid , liquid, and gas in normal terrestrial conditions. Along with oxidane , water is one of the two official names for the chemical compound H 2 O ; [ 50 ] it is also the liquid phase of H 2 O. The addition or removal of heat can cause phase transitions : freezing water to ice , melting ice to water , vaporization water to vapor , condensation vapor to water , sublimation ice to vapor and deposition vapor to ice.
Water differs from most liquids in that it becomes less dense as it freezes. In a lake or ocean, water at 4 °C 39 °F sinks to the bottom, and ice forms on the surface, floating on the liquid water.
This ice insulates the water below, preventing it from freezing solid. Without this protection, most aquatic organisms residing in lakes would perish during the winter. Water is a diamagnetic material.
Det värdefulla vattnet - United Nations Regional Information
At a pressure of one atmosphere atm , ice melts or water freezes solidifies at 0 °C 32 °F and water boils or vapor condenses at °C °F. However, even below the boiling point, water can change to vapor at its surface by evaporation vaporization throughout the liquid is known as boiling. Sublimation and deposition also occur on surfaces. The melting and boiling points depend on pressure.
A good approximation for the rate of change of the melting temperature with pressure is given by the Clausius—Clapeyron relation :. In most substances, the volume increases when melting occurs, so the melting temperature increases with pressure. However, because ice is less dense than water, the melting temperature decreases. At sea level , the boiling point of water is °C °F.