Water anomalous properties

Heuristic approaches remain extremely useful and probably will for a long time. We will show here that a simple model that focuses on the statistics of the hydrogen bonds is qualitatively sufficient for explaining some of the water anomalous properties. 

The anomalous properties of water remain an important subject of inquiry (Errington and Debenedetti, 2001 Mishima and Stanley, 1998). Chaplin (2004) gives a comprehensive overview of 40 anomalous properties of water and suggested explanations. Chaplin (2004) aptly pointed out that whether the properties of water are viewed as anomalous depends on what materials water is compared to and the interpretation of the term anomalous. For example, Angell (2001) included a section on the nonuniqueness of water, stating that. . water is not unique, as is often supposed, but rather water is an intermediate member of a series of substances that form tetrahedral networks of different degrees of flexibility, and that, accordingly, show systematic differences of behavior. Additional references that discuss the properties of water as nonanomalous are Franks (2000), Kivelson and Tarjus (2001), and Netz et al. (2002). 

Ludwig s (2001) review discusses water clusters and water cluster models. One of the water clusters discussed by Ludwig is the icosahedral cluster developed by Chaplin (1999). A fluctuating network of water molecules, with local icosahedral symmetry, was proposed by Chaplin (1999) it contains, when complete, 280 fully hydrogen-bonded water molecules. This structure allows explanation of a number of the anomalous properties of water, including its temperature-density and pressure-viscosity behaviors, the radial distribution pattern, the change in water properties on supercooling, and the solvation properties of ions, hydrophobic molecules, carbohydrates, and macromolecules (Chaplin, 1999, 2001, 2004). 

That the molecules in solid and liquid water interact by hydrogen bonding and that hydrogen bonding is responsible for the anomalous properties of water compared with the other hydrides of Group 16... 

Although water is an excellent solvent and the most popular, it has somewhat anomalous properties that come from the hydrogen bonding ability of water to form three-dimensional networks (Fig. 1.2, Section 1.1.3). Large molecules and ions are often difficult to dissolve in water, unless they have hydrophilic site(s). Therefore, water is not suitable as a medium for reactions involving large hydro-phobic molecules or ions. In contrast, most dipolar aprotic solvents are non-struc-tured or only weakly structured and can dissolve many large molecules and ions. This is another major reason why dipolar aprotic solvents are often used instead of water. 

Anomalous properties—thermal expansivity and thermal conductivity. Molecular simulation has been integral in evaluating physical behaviors of hydrate compared with ice, specifically a larger thermal expansivity (Tse, et al., 1987 Tanaka, et al., 1997) and a glasslike thermal conductivity (Tse, et al., 1983 1984 Inoue, et al., 1996). These properties have been explained by the coupling between the water and the guest molecules. 

The possibility to calculate the anomalous properties of water quantitatively with a simple two step function of the orientations partition function of water molecules gives the possibility to estimate the size of the network of H-bonded molecules in liquid water too. We have to take into account the cooperative mechanism of H-bonds and the preference of C2v symmetry of intermolecular arrangements in... 

We can anticipate that this change will have a marked effect on the properties of H20 when these are compared with other substances (for example, it clearly will change the relative behaviour of the curves discussed in Figure 21.1 Frame 21) and we later show that our predictions are borne out experimentally by the, so called, anomalous properties of pure water, which are, in turn, largely brought about by the existence of hydrogen bonding in water molecules. 

Water is one of the most familiar material in our life and is indispensable to all living things. In contrast to its apparently simple molecular structure, water shows many anomalous properties from both macroscopic and microscopic points of view. However, the basic physical property of water, for example the dynamical structure of water, has not yet been fully clioified. To un rstand the dynamical aspect of water structure and its significant role in life, it is essential to clarify not only the dynamics of water molecules themselves but also the dynamics of water in the aqueous solutions. 

Over 100 years ago, Rontgen and co-workers [28] were already aware of the range of the anomalous properties of water. They postulated that the liquid was... 

Many anomalous properties of water are discussed here ... 

The H-bonding extends through the liquid but this does not mean that the H-bonded structure is fixed and static. Rather it is a dynamic structure with H-bonds constantly being broken and new ones formed. The structure and, on the average, each H-bond exists for a relatively long time of the order of 3 x 10 s. This is a longer time than that for Brownian motion. This dynamic picture of the arrangement of the structure of liquid water was developed to account for the anomalous properties of bulk water, such as the dependence on temperature and pressure of the thermal expansion, compressibility, viscosity and Cp for liquid water. 

The phase diagram for water (shown below) is unusual. The solid/liquid phase boundary slopes to the left with increasing pressure because the melting point of water decreases with increasing pressure. Note that the normal melting point of water is lower than its triple point. The diagram is not drawn to a uniform scale. Many anomalous properties of water are discussed here http //www.lsbu.ac.uk/water/anmlies.html. 

Various qualitative models for water have been proposed to explain its properties and to elucidate its structure. The earlier workers " attempted to explain its anomalous properties by postulating the existence of hydrogen bonds. However, none of these explanations are satisfactory. 

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