Characteristics of water
Source： Time:17 August 2020
Water has unusual characteristics. Water has a huge effect and influence on nature and human life because of these characteristics.
The molecular formula of water is H2O and the relative molecular mass is 18.015. Among water molecules, hydrogen accounts for 11.19% and oxygen accounts for 88.81%. At room temperature, it is a colorless, odorless, and odorless transparent liquid. Pure water is almost non-conductive.
Water has three state changes of solid, liquid and gas. The melting point of water is 0°C and the boiling point is 100°C. It exists as a liquid at room temperature. In industrial production, the characteristics of the three-state change of water in solid, liquid and gas are often used to transform energy.
Water has the smallest volume and the largest density (1g/cm3) at 4°C (actually 3.98°C). Above or below this temperature, the density decreases while the volume expands. This is different from the change law of normal material expansion and contraction. When natural water becomes ice, its volume becomes larger and its density becomes smaller. Because the density of ice (0.917g/cm3) is smaller than that of water, it floats on the water surface, which not only isolates the severe cold temperature, but also protects the survival of underwater creatures, which has a great effect on the existence and evolution of creatures on the earth.
Water has a specific heat capacity greater than that of all liquid and solid substances. Therefore, when the temperature of water increases or decreases by 1°C, the heat absorbed or released by 1g of water is much greater than that of other substances; the temperature of 1g of water rises. Higher or lower 1℃, the heat absorbed or released is about 4.2J (1cal). Water has the largest specific heat of vaporization among all liquids, reaching 2256.7J/g (539.0cal/g) at 100°C; when ice melts into water, its heat capacity will increase by less than twice, while general solids melt , The change in specific heat capacity is very small; when the water is boiling, the water temperature can still be maintained at 100 ℃, and when the ice is melting, the water temperature of the ice-water mixture can still be maintained at 0 ℃.
Water is a very strong solvent, and most substances have great solubility in water. The dielectric constant of water is very large, up to about 80. Water is also very capable of ionizing various solutes, so that various substances dissolved in water can undergo various chemical reactions.
Water has a higher surface tension at room temperature (second only to mercury). At 20°C, the surface tension reaches 72.75*10-3N/m (72.75dyn/cm), while other liquids only have (2.0~5.0)*10- 2N/m(20~50dyn/cm), so the water has obvious capillary phenomenon and wetting effect. This has a significant impact on the life activities of the body and various physical and chemical effects in nature.
Water is also the source of hydrogen for all organic compounds and living substances. The carbon, hydrogen, oxygen and other elements that make up all organic compounds mainly come from water and carbon dioxide in the air. Plants use photosynthesis to convert carbon dioxide and water into various organic life substances. Therefore, all life is closely related to the various characteristics of water.
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