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Physical properties Properties thermodynamic The ice melts with 0°C and water boils with 100°C in constant atmospheric pressure (1 013,25 hPa). Water presents certain anomalies: it contracts with fusion and has a maximum density with 3,98 0C. Beyond, its dilation coefficient is important. Its compressibility is low. Its enthalpy of vaporization gives a constant of Trouton abnormal, close to 26. (This constant, quotient of the molar heat of vaporization by the absolute temperature d’ébullition, is l’entropie molar of vaporization. It is 21 for the majority of the substances.) Its specific heat between 14,5 and 15,5 0C was used to define the calorie, which is the quantity of heat necessary to make traverse such a heating with one gram d’eau. It decrease beyond and passes by a minimum in the vicinity of 35 °C. |
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Other physical properties The viscosity of l’eau is relatively low, its thermal conductibility is fifteen times smaller than that of mercury. C’est a liquid very wetting with respect to glass, qu’il covers perfectly d’une thin film with a contact angle practically no one. Liquid L’eau is transparent under low thickness, blue under great thickness. Opaque in l’infrarouge, c’est a calorific filter. Its absorption in l’ultraviolet is important towards 186 nanometers. Its permittivity is l’une higher. The electric conductivity of l’eau ultra-purified is very low. |
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Physical properties Character oxydoréducteur Sodium reduced water at ambient température
ambiante with ignition:
Whereas the fluorine’oxyde it :
The vapor is oxidizing with respect to many metals and non-metals:
Structure of the liquid The molecule d’eau is a small angular and symmetrical molecule, but its high dipole moment (1,85 Debye) cannot be explained that by l’existence of two pairs will d’électrons free. The two pairs and the two connections are directed tétraédriquement, as in the ice Ih (fig. 2), in which there are hydrogen bonds (connections H) O_H... O resulting from l’interaction between l’hydrogene d’une connection O_H d’une first molecule d’eau and a pair will d’électrons free d’un oxygen d’une another molecule d’eau. Since 1933, J D. Bernal and R. H. Fowler proposed a model of l’eau liquid based on that of the ice. The skeleton ice breaks partially while releasing of l’eau monomeric of which the proportion grows with the temperature. But, in 1965, Stevenson showed that the proportion of monomer was very weak (lower than 5 p. 1000 to 25 °C). That led H. Eyring to propose a model where swarms of 48 molecules d’eau having the density of the Ih ice are dispersed in a solvent of quasi crystalline structure (density of ice III). While melting, the Ih ice is transformed into quasi crystalline liquid III where appear fluctuating gaps and there is contraction. Volume still decrease at increasing temperature jusqu’à 3,98 °C, where the last swarms of the Ih type disappeared. Beyond, there is normal dilation. These concepts introduced into the theory of the liquids d’Eyring make it possible to calculate all the thermodynamic functions of l’eau and l’eau heavy and even viscosities. Water as a solvent L’eau, polar and of great permittivity, bad solvent of made up nonpolar (hydrocarbons), is a good solvent of composed with connections H and electrolytes. The nonpolar aqueous solutions like l’air, methane and l’ethylene are approximately ten thousand times less soluble than l’ammoniac. These compounds reinforce the crystalline structure of l’eau per formation d’« icebergs » around the aqueous solution; l’entropie decreases, as well as solubility. |
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The solubility of the aqueous solutions giving of the connections H varies with the relative weight of the nonpolar part: l’éthanol is entirely soluble whereas butanol l’est only partially as well as phenol, l’éther and trimethylamine. The solubility of proteins and the lipids in l’eau is low. The solubility of l’eau in these compounds l’est also because of the competition enters the hydrogen bonds, the connections molecule-molecule and the bonds molecule-water. The peptide groups can bind to four molecules d’eau, but there is still competition. One can compare with that swelling exchanging resins d’ions. The gel would be due to l’adsorption of l’eau on the surface of colloids. Ionic salts, aqueous solutions, have very varied solubilities: 360 grams per kilogramme d’eau for sodium chloride, 110 grams for potassium sulphate and only 0,7.10-3 G for zinc sulphide. The ions such as La3+, Mg2+, H+, OH- and F (« formative of structures », analogy with the formation d’« icebergs ») are used as cores for the formation d’essaims; there is increase in l’ordre in l’eau. The ions like K+, Na+, ClO4 -, I -, NO3 -, which are hydrated by only one layer of molecules d’eau, inhibit the formation d’essaims: they are « breakers of structures » (Franck). The measurement of l’hydratation of the ions shows that the first are strongly hydrated. In diluted solution, H+ is tétrahydraté (ion H9O4+ of Eigen). The solutions concentrated in acid contain l’ion HÓ+; l’ion free H+ n’exist not. |
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