水(water)

化学元素氢（H）和氧（O）组成的一种物质，分子式为H2O；并以液态、气态（蒸汽、水蒸气）和固态（冰）的形式存在。室温下，水是无色、无嗅、无味的液体。水是最丰富且不可少的化合物，占地表的75%以上。水对生命是必需的，实际上参与了在动植物中发生的每个过程。它最重要的性质之一是能溶解许多其他的物质。水作为溶剂的多用性对活生物体是必需的，生命来源於海洋世界的复杂溶液。活生物体利用水溶液（如血液和消化液）作为实行生物过程的介质。由於水分子是不对称的，因此，不论是在气、液或固态，氢键能使分子排列成特殊的立体构型，从而有效地影响水的性质。许多水的物理和化学性质（如熔点、沸点、黏度、表面张力、液态的密度高於固态）是受氢键的影响。水是非常活泼的物质，自电离性很小，但却极为重要。水在有限的程度上离解为氢离子（H+，使溶液呈酸性）和氢氧离子（OH-，使溶液呈硷性），因此水能有时作为酸，有时作为硷。水有无数种工业用途，包括了溶解剂、稀释剂和氢的来源；它还用於渗透、洗涤、石灰和水泥的水合、纺织、水解、水力学，同时也用在食物和饮料上。亦请参阅hard water、heavy water。

English version：

water

Inorganic compound composed of hydrogen and oxygen (H2O), existing in liquid, gas (steam, water vapor), and solid (ice) states. At room temperature, water is a colorless, odorless, tasteless liquid. One of the most abundant compounds, water covers about 75% of the earth's surface. Life depends on water for virtually every process, its ability to dissolve many other substances being perhaps its most essential quality. Life is believed to have originated in the world's oceans, and living organisms use aqueous solutions (including blood and digestive juices) as mediums for carrying out biological processes. Because water molecules are asymmetric and therefore electric dipoles, hydrogen bonding between molecules in liquid water and in ice is important in holding them together. Many of water's complex physical and chemical properties (high melting and boiling points, viscosity, surface tension, greater density in liquid than in solid form) arise from this extensive hydgrogen bonding. Water undergoes dissociation to the ions H+ (or H3O+) and OH−, particularly in the presence of salts and other solutes; it may act as an acid or as a base. Water occurs bound (water of hydration) in many salts and minerals. It has myriad industrial uses, including as a suspending agent (papermaking, coal slurrying), solvent, diluting agent, coolant, and source of hydrogen; it is used in filtration, washing, steam generation, hydration of lime and cement, textile processing, sulfur mining, hydrolysis, hydraulics, as well as in beverages and foods. See also hard water, heavy water.

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