Our Understanding of Liquid Water

In this chapter we did not investigate the exceptional biological properties of liquid water. The reason is that if it is well known that water is absolutely necessary for life to proceed, at least life as we know it on Earth, it is not evident that the presence of liquid water is a fundamental prerequisite for life to occur. The necessary condition for life to occur seems to be the presence of H2O molecules with their specific ability to build around them an exceptionally dense H-bond network. Even if liquid water is the basic and most simple system that provides such a dense H-bond network, it is not the only one, as dense but slightly different networks may also exist in more locally defined structures with H2O molecules. We examine this point in more details in Ch. 10. 

Up to now, we have examined water in its three states vapour, liquid and solid. Another state has relatively recently revealed to be of interest the supercritical state, where an assembly of water molecules is under a pressure greater than 221 bar (1 bar = 10 Pa) and a temperature higher than 374 °C. In these conditions HjO molecules still establish (weak) H-bonds. They are surprisingly most reactive and are thus candidates to be used in industry to decompose numerous polymers and hazardous chemicals (72). It may for instance rapidly hydrolyse organic molecules without any acidification (73). Supercritical water can thus act as an effective decontamination agent, itself devoid of any toxical effect. Also, its dielectric constant can be continuously varied, as may also its density or the density of H-bonds it contains, etc. How is it so Another open question for that exceptional molecule, and certainly yet a lot of work for scientists. 

Whalley, in Schuster, G. Zundel and C. Sandorfy (Eds.), The Hydrogen Bond Recent Theory and Experiments, Vol. 3, Ch. 29, North Holland, Amsterdam, 1976. 

Chen and J. Teixeira, in I. Prigogine (Ed.), Advances in Chemical Physics, Vol. LXIV, Wiley, 1986. 

Cabane and S. Henon, Liquides, Solutions, Dispersions, Emulsions, Gels, Belin, Paris, 2003. 

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This book is organized into four chapters. The first includes some historical notes and a survey of the main outstanding properties of water. The second chapter presents the theories that have contributed to our understanding of liquid water. Chapter 3 is devoted to extremely dilute solutions of simple solutes in water. This chapter is strictly concerned with the solvation properties of a single solute in pure liquid water. Chapter 4 is an extension of Chapter 3. It contains a discussion of slightly more concentrated aqueous solutions, where pairwise correlations between two solutes are the main subject of interest. 

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