Heat capacities at constant volume, free volumes, and rotational freedom in some liquids

1971 ◽  
Vol 24 (9) ◽  
pp. 1817 ◽  
Author(s):  
DD Deshpande ◽  
LG Bhatgadde
Keyword(s):  
Heat Capacity ◽  
Free Volume ◽  
Heat Capacities ◽  
Organic Liquids ◽  
Velocity Of Sound ◽  
Velocity Data ◽  
Volume Analysis ◽  
Straight Lines ◽  
Rotational Freedom ◽  
Residual Heat

This paper presents the experimental results on the velocity of sound, densities, and heat capacities of eight organic liquids at 25�, 35�, and 45�C. Using Eyring's equation, the free volumes have been calculated from the sound velocity data. For pure liquids, a quantity Cv* = (Cv)L- (Cv)g- Cstr called the residual heat capacity is found to be linearly dependent on free volume. Analysis of the data for 34 liquids shows that a plot of residual heat capacity against the free volume gives a series of straight lines differing in slopes for different groups of liquids such as hydrocarbons, halogen-substituted hydrocarbons, alcohols, etc. This behaviour is ascribed as being due to different degrees of rotational freedom of molecules in these liquids.

scholarly journals Two Faces of the Two Phase Thermodynamic Model

2021 ◽  
Author(s):  
Ádám Madarász ◽  
Andrea Hamza ◽  
Dávid Ferenc ◽  
Imre Bakó
Keyword(s):  
Heat Capacity ◽  
Diffusion Coefficients ◽  
Heat Capacities ◽  
Water Model ◽  
Organic Liquids ◽  
Harmonic Model ◽  
Two Phase ◽  
Self Diffusion ◽  
Anharmonic Correction

<div>The quantum harmonic model and the two-phase thermodynamics method (2PT) are widely used to obtain quantum corrected properties such as isobaric heat capacities or molar entropies. 2PT heat capacities were calculated inconsistently in the literature. For water the classical heat capacity was also considered, but for organic liquids it was omitted. We reanalyzed the performance of different quantum corrections on the heat capacities of common organic solvents against experimental data. We have pointed out serious flaws in previous 2PT studies. The vibrational density of states was calculated incorrectly causing 39 \% relative error in diffusion coefficients and 45 \% error in the 2PT heat capacities. The wrong conversion of isobaric isochoric heat capacity also caused about 40 \% error but in the other direction. We have introduced the concept of anharmonic correction which is simply the deviation of the classical heat capacity from that of the harmonic oscillator model. This anharmonic contribution is around +30-40 J/mol/K for water depending on the water model and -8-10 J/mol/K for hydrocarbons and halocarbons. AC is unrealistically large, +40 J/K/mol for alcohols and amines indicating some deficiency of the OPLS force field. The accuracy of the computations was also assessed with the determination of the self-diffusion coefficients.<br></div>

scholarly journals Two Faces of the Two Phase Thermodynamic Model

2021 ◽  
Author(s):  
Ádám Madarász ◽  
Andrea Hamza ◽  
Dávid Ferenc ◽  
Imre Bakó
Keyword(s):  
Heat Capacity ◽  
Diffusion Coefficients ◽  
Heat Capacities ◽  
Water Model ◽  
Organic Liquids ◽  
Harmonic Model ◽  
Two Phase ◽  
Self Diffusion ◽  
Anharmonic Correction

The quantum harmonic model and the two-phase thermodynamics method (2PT) are widely used to obtain quantum corrected properties such as isobaric heat capacities or molar entropies. 2PT heat capacities were calculated inconsistently in the literature. For water the classical heat capacity was also considered, but for organic liquids it was omitted. We reanalyzed the performance of different quantum corrections on the heat capacities of common organic solvents against experimental data. We have pointed out serious flaws in previous 2PT studies. The vibrational density of states was calculated incorrectly causing 39 % relative error in diffusion coefficients and 45 % error in the 2PT heat capacities. The wrong conversion of isobaric isochoric heat capacity also caused about 40 % error but in the other direction. We have introduced the concept of anharmonic correction (AC) which is simply the deviation of the classical heat capacity from that of the harmonic oscillator model. This anharmonic contribution is around +30-40 J/mol/K for water depending on the water model and -8-10 J/mol/K for hydrocarbons and halocarbons. AC is unrealistically large, +40 J/K/mol for alcohols and amines indicating some deficiency of the OPLS force field. The accuracy of the computations was also assessed with the determination of the self-diffusion coefficients.

Heat capacities and enthalpies of fusion and transformation for solvates of some salts with dimethyl sulfoxide and dimethylformamide

1988 ◽  
Vol 53 (12) ◽  
pp. 3072-3079
Author(s):  
Mojmír Skokánek ◽  
Ivo Sláma
Keyword(s):  
Heat Capacity ◽  
Phase Transformation ◽  
Phase Transformations ◽  
Dimethyl Sulfoxide ◽  
Liquidus Temperature ◽  
Molar Heat Capacity ◽  
Solid Phase ◽  
Zinc Nitrate ◽  
Heat Capacities ◽  
Liquid Phases

Molar heat capacities and molar enthalpies of fusion of the solvates Zn(NO3)2 . 2·24 DMSO, Zn(NO3)2 . 8·11 DMSO, Zn(NO3)2 . 6 DMSO, NaNO3 . 2·85 DMSO, and AgNO3 . DMF, where DMSO is dimethyl sulfoxide and DMF is dimethylformamide, have been determined over the temperature range 240 to 400 K. Endothermic peaks found for the zinc nitrate solvates below the liquidus temperature have been ascribed to solid phase transformations. The molar enthalpies of the solid phase transformations are close to 5 kJ mol-1 for all zinc nitrate solvates investigated. The dependence of the molar heat capacity on the temperature outside the phase transformation region can be described by a linear equation for both the solid and liquid phases.

scholarly journals Calculation of the Isobaric Heat Capacities of the Liquid and Solid Phase of Organic Compounds at 298.15K by Means of the Group-Additivity Method

Molecules ◽  
2020 ◽  
Vol 25 (5) ◽  
pp. 1147
Author(s):  
Rudolf Naef
Keyword(s):  
Experimental Data ◽  
Heat Capacity ◽  
Goodness Of Fit ◽  
Cross Validation ◽  
Solid Phase ◽  
Linear Equations ◽  
Heat Capacities ◽  
Molecular Volume ◽  
Complementary Method ◽  
Standard Deviations

The calculation of the isobaric heat capacities of the liquid and solid phase of molecules at 298.15 K is presented, applying a universal computer algorithm based on the atom-groups additivity method, using refined atom groups. The atom groups are defined as the molecules’ constituting atoms and their immediate neighbourhood. In addition, the hydroxy group of alcohols are further subdivided to take account of the different intermolecular interactions of primary, secondary, and tertiary alcohols. The evaluation of the groups’ contributions has been carried out by solving a matrix of simultaneous linear equations by means of the iterative Gauss–Seidel balancing calculus using experimental data from literature. Plausibility has been tested immediately after each fitting calculation using a 10-fold cross-validation procedure. For the heat capacity of liquids, the respective goodness of fit of the direct (r2) and the cross-validation calculations (q2) of 0.998 and 0.9975, and the respective standard deviations of 8.24 and 9.19 J/mol/K, together with a mean absolute percentage deviation (MAPD) of 2.66%, based on the experimental data of 1111 compounds, proves the excellent predictive applicability of the present method. The statistical values for the heat capacity of solids are only slightly inferior: for r2 and q2, the respective values are 0.9915 and 0.9874, the respective standard deviations are 12.21 and 14.23 J/mol/K, and the MAPD is 4.74%, based on 734 solids. The predicted heat capacities for a series of liquid and solid compounds have been directly compared to those received by a complementary method based on the "true" molecular volume and their deviations have been elucidated.

Free volume analysis of the viscosity of concentrated polymer solutions

Polymer ◽  
1990 ◽  
Vol 31 (8) ◽  
pp. 1486-1490 ◽  
Author(s):  
Hiroshi Fujita ◽  
Yoshiyuki Einaga
Keyword(s):  
Free Volume ◽  
Polymer Solutions ◽  
Volume Analysis
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