Flickering cluster model of liquid water

Frank-Wen flickering cluster model, of liquid water, 26 15, 16 Frascati Manual, 21 610 Frasch sulfur extraction process, 23 564, 570-573... 

Figure 2.8. Flickering cluster model of liquid water. (From Ref. 1 in Section 2.5, with permission from J. Chem. Phys.)...

Fig. 5. (a) Hydrogen-bonded open tetrahedral stmcture of ice (4) (b) Frank-Wen flickering cluster model of liquid water (5). 

The flickering cluster model of liquid water. A given water molecule (circled) is (o) in the middle of a cluster at time ti, (b) at the edge of a different cluster at time fj, and (c) free at time The various water molecules are shown relatively stationary in space from one moment to another. In reality, each would move (translate and rotate) more than is shown here. 

Of the many hypotheses of the structure of liquid water, that ofPople (1951), as modified by Sceats, Stavola and Rice (1979), agrees very well with all experimentally determined properties. In this model, water is formulated as a continuous polymer in which H2O units are united by a network of hydrogen bonds that extend throughout the whole liquid which becomes, in this sense, one large molecule. This formulation is compatible with all recorded physical properties. No support remains for older ideas of flickering clusters , icebergs , monomeric inclusions , or other types of discontinuity. 

With reference to Figure 11.5 showing the involvement of a given water molecule in the liquid, write a short paragraph describing what is meant by the phrase flickering cluster model as applied to the structure of liquid water. 

In order to account for some of the differences in thermodynamic properties of H2O and D2O, theoretical studies have been applied. Swain and Bader first calculated the differences in heat content, entropy, and free energy by treating the librational motion of each water molecule as a three-dimensional isotopic harmonic oscillator. Van Hook demonstrated that the vapor pressure of H2O and D2O on liquid water and ice could be understood quantitatively within the framework of the theory of isotope effects in condensed systems. Nemethy and Scheraga showed that in a model based on the flickering cluster concept, the mean number of hydrogen bonds formed by each water molecule is about 5% larger in D2O than in H2O at 25 °C. 

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