A. Lainez

Thermodynamics of (a halogenated ethane or ethene + an n-alkane). VE and CPE of mixtures containing either 1,1,2,2-tetrachloroethane or tetrachloroethene

Abstract Excess molar volumes V E and excess molar heat capacities C P E at constant pressure have been determined at 298.15 K as a function of mole fraction x 1 for mixtures belonging to series I: {x 1 1,1,2,2-C 2 H 2 Cl 4 + x 2 n-C n H 2n+2 }, and series II: {x 1 C 2 Cl 4 + x 2 n-C n H 2n+2 }, n = 7 and 14. While 1,1,2,2-tetrachloroethane (1,1,2,2-TCE) exhibits trans-gauche rotational isomerism, tetrachloroethene (TCEe) is a rigid molecule without permanent electric dipole moment. The instruments used were a vibrating-tube densimeter and a Picker flow calorimeter. For series I, V E (x 1 =0.5)/(cm 3 .mol −1 ) = 0.153 for n = 7, and 1.029 for n = 14, as compared to −0.192 for n = 7, and 0.313 for n = 14 in series II. The highly asymmetric shape of V E vs. x 1 of (1,1,2,2-TCE + n-C 7 H 16 ) is noted. For series I, the composition dependence of C P E as well as its dependence on n are similar to those for the series (1,2-dichloroethane + an n-alkane) in that for n = 7 the minimum (−2.18 J.K −1 .mol −1 ) is at x 1,min = 0.364 and a shoulder extends to, roughly, x 1 ≈ 0.75. For n = 14, C P E (x 1,min ) = −4.77 J.K −1 .mol −1 at x 1,min = 0.423, and no shoulder is discernible. The curves C P E vs. x 1 for series II are more or less parabolic, with C P E (x 1,min )/(J.K −1 .mol −1 ) = −0.14 at x 1,min = 0.512 for n = 7, and −1.66 at x 1,min = 0.502 for n = 14.

Excess molar quantities of (a halogenated n-alkane + an n-alkane) A comparative study of mixtures containing either 1-chlorobutane or 1,4-dichlorobutane☆

Abstract Excess molar volumes VmE at 298.15 K were obtained, as a function of mole fraction x, for series I: {x1-C4H9Cl + (1 − x)n-ClH2l + 2}, and II: {x1,4-C4H8Cl2 + (1 − x)n-ClH2l + 2}, for l = 7, 10, and 14. 10, and 14. The instrument used was a vibrating-tube densimeter. For the same mixtures at the same temperature, a Picker flow calorimeter was used to measure excess molar heat capacities Cp, mE at constant pressure. VmE is positive for all mixtures in series I: at x = 0.5, VmE/(cm3 · mol−1) is 0.277 for l = 7, 0.388 for l = 10, and 0.411 for l = 14. For series II, VmE of {x1,4-C4H8Cl2 + (1 − x)n-C7H16} is small and S-shaped, the maximum being situated at xmax = 0.178 with VmE(xmax)/(cm3 · mvl−1) = 0.095, and the minimum is at xmin = 0.772 with VmE(xmin)/(cm3 · mol−1) = −0.087. The excess volumes of the other mixtures are all positive and fairly large: at x = 0.5, VmE/(cm3 · mol−1) is 0.458 for l = 10, and 0.771 for l = 14. The Cp, mEs of series I are all negative and |Cp, mE| increases with increasing l: at x = 0.5, Cp, mE/(J · K−1 · mol−1) is −0.56 for l = 7, −1.39 for l = 10, and −3.12 for l = 14. Two minima are observed for Cp, mE of {x1,4-C4H8Cl2 + (1 − x)n-C7H16}. The more prominent minimum is situated at x′min = 0.184 with Cp, mE(x′min)/(J · K−1 · mol−1) = −0.62, and the less prominent at x″min = 0.703 with Cp, mE(x″min)/(J · K−1 · mol−1) = −0.29. Each of the remaining two mixtures (l = 10 and 14) has a pronounced minimum at low mole fraction (xmin = 0.222 and 0.312, respectively) and a broad shoulder around x = 0.7.

Thermodynamics of liquid mixtures containing n-alkanes and strongly polar components: VE and C P E of mixtures with either pyridine or piperidine

Excess molar volumes VE and excess molar heat capacities CP/E at constant pressure have been obtained, as a function of mole fraction x1, for several binary liquid mixtures belonging either to series I: pyridine+n-alkane (ClH2l+2), with l=7, 10, 14, 16, or series II: piperidine+n-alkane, with l=7, 8, 10, 12, 14. The instruments used were a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. VE of pyridine+n-heptane shows a S-shaped composition dependence with a small negative part in the region rich in pyridine (x1>0.90). All the other systems show positive VE only. The excess volumes increase with increasing chain length l of the n-alkane. The excess molar heat capacities of the mixtures belonging to series II are all negative, except for a small positive part for piperidine+n-heptane in the region rich in piperidine (x1>0.87). The CP/E at the respective minima, CP/E(x1,min), become more negative with increasing l, and the x1,min values range from about 0.26 (l=7) to 0.39 (l=14). Most interestingly, mixtures of series I exhibit curves of CP/E against x1 with two minima and one maximum, the so-called W-shape curves.

Mixtures of alkanes with polar molecules showing internal rotation: an unusual composition dependence of CpE of 1,2-dichloroethane + an n-alkane

Abstract Excess molar volumes V E at 298.15 K have been determined as a function of mole fraction x for several mixtures belonging to the series 1,2 – dichloroethane (1,2 – C 2 H 4 Cl 2 ) + an n-alkane (n-C l H 2l+2 ), l = 7,10,14,16. The instrument used was a vibrating-tube densimeter. For the same mixtures and at the same temperature, a Picker flow calorimeter was used to measure excess molar heat capacities C p E at constant pressure. V E is positive for all systems, with V E (x 1 = 0.5 amounting to 0.918 cm 3 .mol −1 for x 1 1,2-C 2 H 4 Cl 2 + x 2 n-C 7 H 16 , and to 1.622 cm 3 mol −1 for x 1 1,2-C 2 H 4 Cl 2 + x 2 n-C 16 H 34 . The results on C p E are strikingly unusual in that for l = 7 a deep minimum is observed at x 1 ≈ 0.3, and a pronounced, rather flat shoulder (almost a second minimum) around x 1 ≈ 0.75. With increasing l, C p E (x 1,min ) becomes more negative and concomitantly the shoulder less prominent. This behavior is reminiscent of the shapes of C p E (x 1 ) reported by Wilhelm (1979a) for mixtures of 1,2 – C 2 H 4 Cl 2 with cyclohexane and methylcyclohexane, and – most interestingly – by Grolier (1984) and Inglese (1982, 1984) for mixture of cyclic diethers with n-alkanes and cyclohexane.

Excess molar volumes and heat capacities of (1,2,4-trichlorobenzene + an n-alkane) and (1-chloronaphthalene + an n-alkane)

Abstract Excesss molar volumes V m E at 298.15 K were obtained, as a function of mole fraction x , for several mixtures belonging either to series I: { x 1,2,4-C 6 H 3 Cl 3 + (1− x ) n -C l H 2 l +2 }, or series II: { x 1-C 10 H 7 Cl+(1− x ) n -C l H 2 l +2 }, for chain lengths 7⩽ l ⩽16. The instrument used was a vibrating-tube densimeter. At the same temperature, a Picker flow calorimeter was used to determine excess molar heat capacities C p,m E at constant pressure. For both series, the V m E values increase with increasing l . In series I, V m E for l = 7 is negative, for l = 12 it is very small and S-shaped, and for 1 = 16 it is positive over the whole composition range. V m E is negative for both mixtures ( l = 14 and 16) of series II. The excess molar heat capacities of the mixtures belonging to series I are all negative, while those of series II are all positive. For both series the plot C E p,m ( x = 0.5) against l shows a maximum (for series I at roughly l = 10, and for series II at about l = 11).

Excess molar heat capacity and excess molar volume of 1,6-dichlorohexane + n-octane

Abstract Excess molar volumes, V E , at 298. 15 K were determined, as a function of mole fraction, x , for { x 1, 6 − C 6 H 12 Cl 2 + (1 − x ) n − C 8 H 18 }. V E is small and shows S-shaped composition dependence. For the same mixture at the same temperature, a Picker flow calorimeter was used to determine excess molar heat capacities, C E P , at constant pressure. C E P is negative with a minimum at, roughly x = 0.2, and a pronounced, rather flat, shoulder around x = 0.6. This behavior is similar to that found previously with (1,2-dichloroethane+an n -alkane) and (1,4-dichlorobutane + an n -alkane).

Heat capacities and concentration fluctuations in mixtures of 1,2-dibromoethane with alkanes

Excess volumes, excess heat capacities and light scattering have been measured for several 1,2-dibromoethane–alkane (n-heptane, n-octane, n-tetradecane, cyclooctane and 2,2,4-trimethylpentane) systems. The results show that there is good agreement between values of the concentration–concentration correlation function Scc, as calculated from light-scattering data, and the predictions of the simple rigid lattice model of Flory and Huggins, which estimates the relative effects of the differences in molecular sizes and of differences in the interaction energies of the two components. The results also confirm the utility of Scc as predictor of the existence of W-shaped excess isobaric heat capacity (CEP) curves, although other effects, such as the destruction of the (partial) correlation of molecular orientation may complicate this issue.

Thermodynamics of (1,4-difluorobenzene + an n-alkane) and of (hexafluorobenzene + an n-alkane)

Excess molar enthalpies HE and excess molar volumes V E have been measured, as a function of mole fraction x 1 , at 298.15 K and atmospheric pressure for the five liquid mixtures (x 1 1,4-C 6 H 4 F 2 + x 2 n-C i H 2l+2 ), l = 7, 8, 10, 12 and 16. In addition, HE and excess molar heat capacities C P E at constant pressure have been determined for the two liquid mixtures (x 1 C 6 F 6 +x 2 n-C l H 2l+2 ), l=7 and 14, at the same temperature and pressure. The instruments used were flow microcalorimeters of the Picker design (the HE version was equipped with separators) and a vibrating-tube densimeter, respectively. The excess enthalpies of the five difluorobenzene mixtures are all positive and quite large ; they increase with increasing chain length l of the n-alkane from H E (x 1 = 0.5)/(J mol -1 ) = 1050 for l=7 to 1359 for l=16.

Thermodynamics of liquid mixtures containing hydrocarbons and strongly polar substances:VE andCPE of {pyridine or piperidine+cyclohexane} at 298.15 K

SummaryExcess molar volumesVE and excess molar heat capacitiesCPE at constant pressure have been determined, as a function of mole fractionx1 at 298.15 K and atmospheric pressure, for the two liquid mixtures {pyridine or piperidine+cyclohexane}. The instruments used were a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. The two systems show positive excess volumes withVE(x1=0.5)=0.531 cm3·mol−1 for {pyridine+cyclohexane} and 0.295 cm3·mol−1 for {piperidine+cyclohexane}. The curveCPEvs. x1 for {pyridine+cyclohexane} shows a rather complex S-shape:CPE is negative at small mole fractionsx1 of pyridine and positive forx1>0.22, roughly.CPE of the piperidine system is negative throughout and strongly asymmetric with the minimumCPE(x1,min)=−2.32J·K−1·mol−1 being situated at a mole fraction of piperidinex1,min≈0.27.ZusammenfassungFür die beiden flüssigen Mischungen {Pyridin oder Piperidin+Cyclohexan} wurden molare ZusatzvoluminaVE und molare ZusatzwärmekapazitätenCPE bei konstantem Druck als Funktion des Molenbruchsx1 bei 298.15K bestimmt. Die Messungen wurden mit einem Biegeschwinger-Dichtemeßgerät bzw. einem Strömungsmikrokalorimeter nach Picker durchgeführt. Die Zusatzmolvolumina beider Systeme sind positiv mitVE(x1=0.5)=0.531 cm3·mol−1 für {Pyridin+Cyclohexan} und 0.295 cm3·mol−1 für {Piperidin+Cyclohexan}. Die KurveCPEvs. x1 des Systems {Pyridin+Cyclohexan} zeigt einen ungewöhnlichen S-förmigen Verlauf: bei kleinen Molenbrüchenx1 von Pyridin istCPE negativ, fürx1>0.22 istCPE positiv. Die molare Zusatzwärmekapazität des Piperidinsystems ist überall negativ und stark unsymmetrisch: im Minimum beix1,min≈0.27 findet manCPE(x1,min)=−2.32J·K−1·mol−1.