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Using the literature raw data of the speed of sound and the specific volume, the isothermal compressibility, κT, a second derivative thermodynamic quantity of G, was evaluated for liquid H2O in the pressure range up to 350 MPa and the temperature to 50 ºC. We then obtained its pressure derivative, dκT/dp, a third derivative numerically without using a fitting function to the κT data. On taking yet another p-derivative at a fixed T graphically without resorting to any fitting function, the resulting d2κT/dp2, a fourth derivative, showed a weak but clear step anomaly, with the onset of the step named point X and its end point Y. In analogy with another third and fourth derivative pair in binary aqueous solutions of glycerol, dαp/dxGly and d2αp/dxGly2, at 0.1 MPa (αp is the thermal expansivity and xGly the mole fraction of solute glycerol) in our recent publication [J. Solution Chem. 43, 663-674 (2014); DOI:10.1007/s10953-013-0122-7], we argue that there is a gradual crossover in the molecular organization of pure H2O from a low to a high p-regions starting at point X and ending at Y at a fixed T. The crossover takes place gradually spanning for about 100 MPa at a fixed temperature. The extrapolated temperature to zero p seems to be about 70 – 80 °C for points X and 90 – 110 °C for Y. Furthermore, the mid-points of X and Y seem to extrapolate to the triple point of liquid, ice Ih and ice III. Recalling that the zero xGly extrapolation of point X and Y for binary aqueous glycerol at 0.1 MPa gives about the same T values respectively, we suggest that at zero pressure the region below about 70 °C the hydrogen bond network is bond-percolated, while above about 90 ºC there is no hydrogen bond network. Implication of these findings is discussed.

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“…The appropriateness of such approximation was discussed at some length earlier. 20 Results are plotted in Fig. 4.…”

Section: Resultsmentioning

confidence: 99%

Gradual crossover in molecular organization of stable liquid H2O at moderately high pressure and temperature

et al. 2014

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“…According to Eqs. (15) and (13) [8,9] and the data on the concentration dependences of volume properties of mixtures from [10][11][12][13][14][15]. We studied mixtures of different types, including mixtures comprising liquids with 1) predominantly van der Waals interactions, 2) hydrogen bonds, and 3) both interaction types.…”

Section: Structural Model Of a Realistic Mixturementioning

confidence: 99%

Influence of the geometric factor on the volume properties of triple mixtures

Balankina

2009

Russ Phys J

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For model mixtures it is established that the concentration behavior of the molar volume that obeys the additive rule with respect to mole fraction is explained by the difference in geometric structures of pure liquids constituting mixture. It is revealed that the geometric factor (the difference in volumes of molecules and packing densities of the initial liquids constituting mixture) brings significant contribution to the excess molar volume of water mixtures of nonelectrolytes. Within the framework of the suggested approach, a maximum contribution of this factor to the relative excess volume of triple mixtures is estimated.

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“…As we have pointed out earlier [4][5][6], this route of obtaining the partial molar quantity tends to introduce systematic errors and is rather dangerous to obtain the next derivative quantity from the fitted polynomial. We have therefore taken the derivatives either graphically [4][5][6], or numerically if the quality of raw mother data are of high quality and in small enough increments [7]. While the latter routes provide the resulting derivatives with sizable random errors, the systematic errors in the curve-fitting sometimes mask an important variation in the resulting derivative.…”

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“…For calculating C pW E and V W E , however, the author fitted a third order polynomial to the raw data of mother quantities (C p E for the former and V E for the latter) and differentiated the polynomial arithmetically [1,2]. As we have pointed out earlier [4][5][6], this route of obtaining the partial molar quantity tends to introduce systematic errors and is rather dangerous to obtain the next derivative quantity from the fitted polynomial. We have therefore taken the derivatives either graphically [4][5][6], or numerically if the quality of raw mother data are of high quality and in small enough increments [7].…”

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confidence: 99%

“…Having smoothed C p data, we then approximate the derivative with the quotient calculated by the smoothed data points. The appropriateness of this approximation was checked acceptable when the quotients converged when the size of δx TBA is reduced, and for TBA-H 2 O δx TBA = 0.004 was found adequate [4,6]. (4) & (5) The three sets of C p data were used to curve-fit the third order polynomial as the author did [1].…”

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confidence: 99%

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To curve-fit or not to curve-fit: Comments on “Water structure enhancement in water-rich binary solvent mixtures. Part II. The excess partial molar heat capacity of the water” by Yizhak Marcus in this journal

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Cited by 68 publications

References 25 publications

Gradual crossover in molecular organization of stable liquid H2O at moderately high pressure and temperature

Gradual crossover in molecular organization of stable liquid H2O at moderately high pressure and temperature

Influence of the geometric factor on the volume properties of triple mixtures

To curve-fit or not to curve-fit: Comments on “Water structure enhancement in water-rich binary solvent mixtures. Part II. The excess partial molar heat capacity of the water” by Yizhak Marcus in this journal

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