Negative Excess Molar Volumes Research Articles

Density Measurement of Molten NdCl3-NaCl and NdCl3-KCl Systems by Gamma Ray Attenuation

Densities of molten chlorides mixture of NdCl3-NaCl and NdCl3-KCl systems have been measured using-ray attenuation method as a function of temperature. Gamma-ray spectra of Ho-166m radiation source were taken before and after passing through the molten chlorides in a quartz cell by a Ge-detector coupled with multi-channel pulse analyzer. The density was calculated with observed attenuation factor, cross section data of photons for relevant elements and length of the cell. The length of the cell was also determined with the attenuation factor observed on water, cross section data of photons for water and density of pure water at room temperature. The measured densities of molten NdCl3-NaCl and NdCl3-KCl systems were compared with literature data by dilatometric method. The excess molar volume isotherm at 1100 Kelvin for NdCl3-NaCl and NdCl3-KCl systems showed the maximum at NdCl3 composition of around 0.2. A small negative excess molar volume was found at NdCl3composition of 0.75 for NdCl3-NaCl system.

Excess molar volumes and isentropic compressibilities of binary liquid mixtures containing n-alkanes at 298.15 K

Excess molar volumes (V E) and deviation in isentropic compressibilities (Δβ s) have been investigated from the density ρ and speed of sound u measurements of six binary liquid mixtures containing n-alkanes over the entire range of composition at 298.15 K. Excess molar volume exhibits inversion in sign in one binary mixture, i.e., n-heptane + n-hexane. Remaining five binary mixtures, n-heptane + toluene, cyclohexane + n-heptane, cyclohexane + n-hexane, toluene + n-hexane and n-decane + n-hexane show negative excess molar volumes over the whole composition range. However, the large negative values of excess molar volume becomes domainant in toluene + n-hexane mixture. Deviation in isentropic compressibility is negative over the whole range of composition in the case of all the six binary mixtures. Existence of specific intermolecular interactions in the mixtures has been analyzed in terms of excess molar volume and deviation in isentropic compressibility.

Density and excess molar volumes of aqueous solutions of morpholine and methylmorpholine at temperatures from 298.15 K to 353.15 K

Densities of (water + morpholine) and (water + methylmorpholine) have been measured over the full range of compositions at temperatures from 298.15 K to 353.15 K. Density values have been used for calculations of excess molar volumes and partial molar volumes of morpholine and methylmorpholine in the mixtures. The effect of the additional methyl group on the methylmorpholine compared to morpholine is reflected in a lower density value and a more negative excess molar volume.

Thermodynamics of Liquid Mixtures of Xenon with Alkanes: (Xenon + n-Butane) and (Xenon + Isobutane)

The total vapor pressure of liquid mixtures of (xenon + n-butane) has been measured at 182.34 and 195.49 K, and of (xenon + isobutane) at 195.49 K. The liquid molar volumes have also been measured at 182.34 K for both systems. The mixtures follow the behavior already found for other (xenon + alkane) mixtures, i.e., negative deviations from Raoult's law, negative excess molar Gibbs energies ( ) and negative excess molar volumes ( ). The excess molar enthalpy ( ) is approximately zero in the case of (xenon + n-butane). The results were interpreted using the statistical association fluid theory for potentials of variable attractive range (SAFT-VR). This study provides further evidence that the (xenon + n-alkane) mixtures can be thought of as a particular case of mixtures of n-alkanes.

Thermodynamics of liquid mixtures consisting of a very polar and a non-polar aromatic: (benzonitrile + benzene, or toluene)

For the two binary liquid systems {xC6H5CN+(1−x)C6H6} and {xC6H5CN+(1−x)C6H5CH3}, excess molar volumesVEm, excess molar enthalpiesHEm, and excess molar heat capacitiesCEp,mat constant pressure have been measured as a function of mole fractionx. Values ofVEmwere determined atT=(298.15, 308.15, and 318.15)K,HEmwas determined atT=(293.15, 298.15, and 303.15)K, andCEp,mwas determined atT=298.15K (all at atmospheric pressure). The instruments used were, respectively, a vibrating-tube densimeter (from Sodev), an LKB differential flow microcalorimeter equipped with two computer-controlled h.p.l.c. piston pumps (from Gilson), and a Picker flow microcalorimeter (from Setaram). In addition, isobaric heat capacities divided by volumeCp,m/Vmof the pure liquids, as well as several selected mixtures, were measured with a programmable differential scanning calorimeter of the Calvet type (micro-d.s.c., from Setaram) between approximatelyT=280K andT=350K. Both systems show relatively small negative excess molar volumes, which become more negative with increasing temperature. The excess molar enthalpies are highly unusual in that for both systems an M-shaped composition dependence is observed (twomaxima andoneminimum). The M-shape is much more prenounced for (benzonitrile+toluene) than for (benzonitrile+benzene), and appears to vanish for the latter system belowT=298.15K. The results can be understood in terms of a simple theory of complex formation (Guggenheim–McGlashan). The excess molar heat capacity at constant pressure atT=298.15K of (benzonitrile+toluene) is positive at all compositions, while that of (benzonitrile+benzene) is positive only for 0<x<0.071, and negative otherwise (sigmoidal shape). Combining the heat capacities obtained with the Picker calorimeter atT=298.15K with our results forCp,m/Vmobtained with the micro-d.s.c. in conjunction with our density data, excess molar heat capacities have also been derived for (benzonitrile+toluene) atT=(288.15, 308.15, 318.15, and 328.15)K. For this system, the maximum of the curveCEp,magainstxbecomes somewhat smaller with increasing temperature and is shifted towards larger values ofx,i.e.the curves become more symmetric.

Limiting partial molar volumes and expansions for triethylamine in water and in aqueous tetraethylammonium chloride solutions from 15 to 35°C

The densities of ternary systems of triethylamine in aqueous tetraethylammonium chloride solutions have been measured, at 5 °C intervals from 15 to 35 °C, with a vibrating tube densimeter. The molalities in tetraethylammonium chloride studied were 0, 0.05, 0.4 and 0.9 mol kg −1 . The concentration of triethylamine was varied from 0 to ca. 0.35 mol kg −1 in each solvent. Negative excess molar volumes, V m E , were obtained for all the systems and their variations with the amine mole fraction were fitted to the Redlich–Kister equation. Limiting partial molar volumes and expansions of triethylamine, V Et3 N ∞ and E P,Et3 N ∞ , were evaluated using the derivatives dV m E /dx Et3 N and dV Et3 N ∞ /dT, respectively. Values of V Et3 N ∞ increase with temperature for all the solvents. Limiting excess partial molar volumes of triethylamine, V Et3 N E,∞ , are considerably negative and decrease with the salt concentration. This means a shift from ideality in the direction of a better packing efficiency of Et 3 N in the cage structure of the water and this effect increases as the concentration of the salt is increased. Values of E P,Et3 N ∞ are all positive and increase with the salt concentration. This may signify that the accommodation of Et 3 N in the water structure decreases with temperature. Molar expansions were also derived and plotted vs. the amine concentration.

Densities and viscosities of binary aqueous mixtures of nonelectrolytes: tert-Butyl alcohol and tert-butylamine

The density and shear viscosity of mixtures of tert-butyl alcohol (BuOH) and tert-butylamine (TBA) with water have been determined for various temperatures (288 to 318 K for H2O + BuOH and 288 to 308 K for H2O + TBA) over the whole composition range. Excess molar volumes and apparent molar volumes of the components of each system were calculated from the density data. In both systems the apparent molar volume of the organic component passes through a minimum in the water-rich region. Both systems exhibit large negative excess molar volumes which are essentially independent of temperature at all compositions. The two systems show pronounced maxima in their shear viscosity isotherms.

Excess heat capacities and excess volumes of (an n-alkylalkanoate + heptane or decane or toluene)

Excess molar heat capacities C E p,m at constant pressure have been determined, as a function of mole fraction x at the temperature T = 298.15 K and atmospheric pressure, for eight liquid mixtures: [(1 - x)C 6H 5CH 3 + x {HCO 2(CH 2) 2CH 3 or HCO 2(CH 2) 3CH 3 or CH 3CO 2C 2H 5 or CH 3CO 2(CH 2) 2CH 3 or CH 3CO 2(CH 2) 3CH 3 or CH 3CH 2CO 2CH 3 or CH 3CH 2CO 2C 2H 5 or CH 3CH 2CO 2(CH 2) 2CH 3}] and four more liquid mixtures: [(1 - x ){CH 3(CH 2) 5CH 3 or CH 3(CH 2) 8CH 3} + x {CH 3CO 2(CH 2) 2CH 3 or CH 3(CH 2) 2CO 2(CH 2) 2CH 3}]. Excess molar volumes V E m have been determined, as a function of x at the same temperature and pressure, for the eight mixtures containing C 6H 5CH 3 and for [ xCH 3CO 2(CH 2) 2CH 3 + [1 - x){CH 3(CH 2) 5CH 3 or CH 3(CH 2) 8CH 3}]. The instruments used were a Picker flow microcalorimeter and a vibrating-tube densimeter, respectively. The two mixtures: (propylethanoate + an n-alkane) show positive excess volumes; the mixtures containing C 6H 5CH 3 show either small positive excess molar volumes with V E m( x = 0.5)/{cm 3·mol -1) = 0.045 {with HCO 2(CH 2) 2CH 3} and =0.021 {with HCO 2(CH 2) 3CH 3}, or negative excess molar volumes, the more negative being with CH 3CH 2CO 2(CH 2) 2CH 3: V E m( x = 0.5)/(cm 3·mol -1) = -0.181. The curves of C E p,m against x for [(1 - x ){CH 3(CH 2) 5CH 3 or CH 3(CH 2) 8CH 3} + x CH 3CO 2(CH 2) 2CH 3] show W-shaped behaviour. C E p,m s for the mixtures containing C 6H 5CH 3 are rather small, either slightly positive or S-shaped, with a negative part always situated at high mole fractions x of the n-alkanoate.

Alkyl-chain-length dependence of the excess volumes for (an α,ω-dichloroalkane + an alkan-2-one)

Excess molar volumes V E m at the temperature T = 298.15 K and normal atmospheric pressure were obtained for { xCH 2Cl(CH 2) p-2 CH 2Cl + (1 - x )CH 3CO(CH 2) q-3 CH 3} for p = 5 or 6 and for q = 3 or 4 or 5 or 6. Experimental V E m values were determined from densities measured using a vibrating-tube densimeter. All the mixtures studied exhibit negative excess molar volumes, which become more negative when the length of the α,ω-dichloroalkane increases. The characteristics of the excess molar volumes are compared with those of the excess molar enthalpies of the same mixtures.

Excess molar volume and m/m* effects in the magnetic behaviour of liquid HgNa alloys

The magnetic susceptibility of liquid-mercury-based alloys containing 5, 8, 15 and 18 at.% Na is investigated. Changes in the paramagnetic contribution of the conduction electrons are discussed in terms of negative excess molar volume. The anomalous variation of the total magnetic susceptibility with the composition is analysed. The occurrence of Hg4 units appears to be corroborated from the composition dependence of the effective mass ratio m/m*.