Global Water Cycle: The Three Phases Of Water

Global Water Cycle.

1. The exchange of water among the ocean, the land and the atmosphere is termed as the hydrologic or water cycle. The sun’s heat evaporates surface water from the ocean and the land, akin to leaving a glass of water in sunlight for a few weeks and observing the changes. Evaporated water enters the atmosphere as vapour and most of this returns directly to the sea as precipation. Air currents transports the remainder of this water vapour over land, where it condenses and falls as rain or snow. This precipitation flows as run off into rivers. Collects temporarily in lakes, pondsand wetlands, infiltrates the ground only to rise later in rivers, lakes and ponds or as remains in sold form as snow or ice. With passage of time,

Hydrogen Bonding. The water consists of two hydrogen atom and one oxygen atom bonded by hydrogen bonds. It occurs because water molecules do not have an equal distribution of electric charge across the molecule, contributing a degree of attraction between oppositely charged ends of water molecules. Whereas similar chemicals which lack hydrogen bonds are gases at earth surface temperatures. The presence of peculiar hydrogen bond explains high viscosity and low compressibility and High surface tension.

4.1.2. Three Phases of Water. Water is one of the few substances to occur naturally in three phases i.e solid(ice), liquid(water) and gas (water vapour infact is not a true gas). The density of water is greater than water vapour because the molecules are more ordered and closer together. The solid phase possesses the most orderly molecular structure.

4.1.3. Heat Capacity. Water has a high heat capacity and a high latent heat, large amount of heat are required to change water between liquid and solid and between liquid and vapour states. Oceans are important heat store and exert a long-term control on climate. For oceans the consequences of water’s high heat capacity are of truly immense proportions. Water’s latent heats of melting, vaporization, evaporation, condensation and freezing play a pivotal role in the global thermostatic effects affecting climatic

Although the major constituents can be removed from oceans by chemical and biological processes, removal generally would have less overall effect on the concentration of the constituent as they are stable over time. They are said to have conservative behaviour, on the other hand, rate at which water mixes through the ocean is much faster than the rate at which these constituents are supplied or removed, hence variations are observed in their concentration owing to difference in physical processess such as evaporation , melting and mixing, However the “Ratios” of these elements is almost constant under most conditions. This is known generally as Principle of Constant Proportions and has important bearing on determination of saltiness of seas. (OES)

5.2. The total quantity of dissolved solids present in the waters of the oceans can be gauged by an assumption of an average salinity of 35% and volume of ocean being 1.37 x 10 9 km3 with a density insitu of 1.04. The dissolved solids would amount to 5x10-16 metric tons which means this would form a layer of dried salts 45 m thick over the entire earth or 153m thick over the present land area. The trace elements are also in abundance, if extraction techniques for rare/trace elements is economically viable, oceans may well serve as everlasting source of these elements.(chem of