Molar Enthalpies Of Solution Research Articles

Gas-Liquid Phase Boundary Lines and Critical Curve for the Water+Methane System

The isothermal gas-liquid phase boundary lines and critical curve were determined for the water+methane system.Experiments were performed in a high-pressure volume-variable autoclave with a sapphire window and magnetic stirring.The temperature range was from 433.0 to 633.0 K and pressure from 30.00 to 300.00 MPa.Henry coefficients of dilute methane solutions were determined;the results show that these coefficients decrease with increasing temperature in the range from 433.0 to 603.0 K.The equilibrium gas-liquid ratios,partial molar solution enthalpy,and partial molar solution entropy were also calculated.The results show that the difference in the cohesive energy density between methane and water is very large.

Thermodynamic properties of microporous crystals of Na2[ZnB3P2O11(OH)]·0.67H2O

The pure hydrated metalloborophosphate with microporous structure, Na2[ZnB3P2O11(OH)]·0.67H2O, has been synthesized under hydrothermal conditions and characterized by XRD, FT-IR, DTA-TG techniques and chemical analysis. The molar enthalpies of solution of Na2[ZnB3P2O11(OH)]·0.67H2O (s) in 1mol·dm−3 HCl (aq), and of NaH2PO4·2H2O (s) in (HCl+H3BO3+ZnO) (aq) were measured, respectively. With the incorporation of the previously determined enthalpies of solution of H3BO3 (s) in 1mol·dm−3 HCl (aq), and of ZnO (s) in (HCl+H3BO3) (aq), together with the use of the standard molar enthalpies of formation for NaH2PO4·2H2O (s), ZnO (s), H3BO3 (s) and H2O (l), the standard molar enthalpy of formation of −(5200.3±2.5)kJ·mol–1 for Na2[ZnB3P2O11(OH)]·0.67H2O at T=298.15K was obtained on the basis of the appropriate thermochemical cycle.

Study on the enthalpy of solution and enthalpy of dilution for the ionic liquid [C 3mim][Val] (1-propyl-3-methylimidazolium valine)

A new amino acid ionic liquid (AAIL) [C 3mim][Val] (1-propyl-3-methylimidazolium valine) was prepared by the neutralization method. Using the solution-reaction isoperibol calorimeter, molar solution enthalpies of the ionic liquid [C 3mim][Val] with known amounts of water and with different concentrations in molality were measured at T = 298.15 K. In terms of standard addition method (SAM) and Archer’s method, the standard molar enthalpy of solution for [C 3mim][Val] without water, Δ s H m ∘ = (−55.7 ± 0.4) kJ · mol −1, was obtained. The hydration enthalpy of the cation [C 3mim] +, Δ H + ([C 3mim] +) = −226 kJ · mol −1, was estimated in terms of Glasser’s theory. Using the RD496-III heat conduction microcalorimeter, the molar enthalpies of dilution, Δ D H m( m i → m f), of aqueous [C 3mim][Val] with various values of molality were measured. The values of Δ D H m( m i → m f) were fitted to Pitzer’s ion-interaction model and the values of apparent relative molar enthalpy, φL , calculated using Pitzer’s ion-interaction model.

Hydration of Thiourea and Mono-, Di-, and Tetra-N-Alkylthioureas at Infinite Dilution: A Thermodynamic Study at a Temperature of 298.15 K

Molar enthalpies of solution in water, ΔsolHm, of thiourea, methylthiourea, ethylthiourea, dimethyl-1,3-thiourea, diethyl-1,3-thiourea, and tetramethyl-1,1,3,3-thiourea were measured at T = (296.84...

Saturation molalities and standard molar enthalpies of solution of α-d-xylose(cr) in H2O(l); standard molar enthalpies of solution of 1,4-β-d-xylobiose(am), and 1,4-β-d-xylotriose(am) in H2O(l)

The saturation molality of α-d-xylose(cr) in water was measured by using HPLC and is m(sat)=(8.43±0.42)mol·kg−1 at T=298.15K. It was also established that the anhydrous form of α-d-xylose(cr) is the crystalline form that is in equilibrium with the aqueous solution at T=298.15K. Solution calorimetry was used to measure the following standard molar enthalpies of solution at T=298.15K: ΔsolHm∘=(12.10±0.12)kJ·mol−1 for α-d-xylose(cr); ΔsolHm∘=−(8.1±2.7)kJ·mol−1 for 1,4-β-d-xylobiose(am); and ΔsolHm∘=−(24.1±6.4)kJ·mol−1 for 1,4-β-d-xylotriose(am). It was observed that both 1,4-β-d-xylobiose(am) and 1,4-β-d-xylotriose(am) were amorphous substances and that they form thick gels in water in which no solid phase is present. Consequently, it is not possible to measure m(sat) for these two substances. All substances were carefully characterized by using both HPLC and Karl Fischer analysis. NMR was used to measure the anomeric purity of the α-d-xylose(cr). Thermodynamic network calculations were used to calculate standard molar formation properties for the aforementioned substances.

Hydrothermal Synthesis and Thermodynamic Property of the Zeolite-Like Galloborate of K2[Ga(B5O10)]·4H2O

The pure zeolite-like galloborate of the K2[Ga(B5O10)]·4H2O sample has been synthesized by a mild hydrothermal method and characterized by means of chemical analysis, XRD, FT-IR, and DTA-TG techniques. The molar enthalpies of solution of KGa(SO4)2·12H2O(s) in the mixture of 1 mol·kg−1 HCl and calculated amount of K2B4O7·4H2O, of K2SO4(s) in the mixture of 1 mol·kg−1 HCl and calculated amount of H3BO3, of K2[Ga(B5O10)]·4H2O(s) in the mixture of 1 mol·kg−1 HCl and calculated amount of K2SO4 and H3BO3 at 298.15 K were measured, respectively. With the incorporation of the previously determined enthalpies of solution of H3BO3(s) and K2B4O7·4H2O(s) in 1 mol·kg−1 HCl, together with the use of the standard molar enthalpies of formation for K2B4O7·4H2O(s), KGa(SO4)2·12H2O(s), K2SO4(s), H3BO3(s), and H2O(l), the standard molar enthalpy of formation of −(5768.5 ± 9.1) kJ·mol−1 for K2[Ga(B5O10)]·4H2O(s) was obtained on the basis of the appropriate thermochemical cycle. In addition, the standard molar enthalpy of formation of −(5757.6 ± 0.8) kJ·mol−1 for KGa(SO4)2·12H2O(s) was also obtained according to its molar enthalpy of solution of (45.15 ± 0.11) kJ·mol−1 in H2O at 298.15 K.

Thermochemistry of 2-Aminopyridine (C5H6N2)(s)

The molar enthalpies of solution of 2-aminopyridine at various molalities were measured at T = 298.15 K in double-distilled water by means of an isoperibol solution- reaction calorimeter. According to Pitzer's theory, the molar enthalpy of solution of the title compound at infinite dilution was calculated to besolH ∞ m = 14.34 kJ · mol −1 , and Pitzer's ion interaction parameters β ( 0)L MX ,β (1)L MX ,a ndC φL MX were obtained. Values of the relative ap- parent molar enthalpies ( φ L) and relative partial molar enthalpies of the compound ( ¯ L2) were derived from the experimental enthalpies of solution of the compound. The standard molar enthalpy of formation of the cation C5H7N + in aqueous solution was calculated to be � fH o m(C5H7N + 2 , aq) =− (2.096 ± 0.801) kJ · mol −1 .

Calorimetric investigation of reaction Ca(NO3)2 + Na3PO4 in water and microemulsions saturated with CO2

AbstractThe reactions of Ca(NO3)2 + Na3PO4 in water and water/sodium bis(2‐ethylhexyl) sulfosuccinate (AOT)/hydrocarbon microemulsions saturated CO2 with various molar ratios of water to surfactant R, oil phases, and surfactant concentrations were investigated by isothermal titration calorimetry. The product of the reaction was confirmed to be sodium‐and‐carbonate‐substituted hydroxyapatite (NaCO3HAP) by Fourier transform infrared spectra (FTIR), energy dispersive spectrometry (EDS), and X‐ray diffraction (XRD). From calorimetric measurements, the molar enthalpies of solution of water in the AOT/n‐dodecane system, and the molar enthalpies, the rate constants, and the activation energies of the reactions were determined. It was found that the enthalpy of solution of water in AOT/n‐dodecane micells and the molar enthalpy of the reaction in the microemulsions increased with the decreases of R until R = 7; below that they kept almost constant. It may be attributed to the increase of the ratio of the bound water to the free water with the decrease of R until there was no free water when R < 7. However, the reaction rate constant k1 was affected by the ionic strength of the medium and log k1 showed a linear dependence on 1/R in the whole range of R we investigated. It was also observed that the rate constant and the enthalpy of the reaction remained almost unchanged when the surfactant concentration and the nature of oil phase varied. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 322–330, 2011

Temperature Dependence of Vapor Pressures over Saturated Aqueous Solutions at Invariant Points of the NaCl + KNO3 + H2O, NaCl + Na2CO3 + H2O, and NaCl + Na2SO4 + H2O Systems

Vapor pressures of water over saturated solutions with regard to two salts, in the NaCl + KNO3 + H2O, NaCl + Na2CO3 + H2O, and NaCl + Na2SO4 + H2O systems are reported in the (278 to 323) K temperature range. The determined vapor pressures were used to obtain the water activities, the molar enthalpies of vaporization and the osmotic coefficients. Compositions of invariant points from the literature were correlated as a function of temperature with the aid of quadratic equations. These equations served to determine the molar enthalpies of solution.

Complexation of nevirapine with β-cyclodextrins in the presence and absence of Tween 80: characterization, thermodynamic parameters, and permeability flux

Abstract The work is undertaken to evaluate the effect of Tween 80 on the complexing ability of β-cyclodextrins to encapsulate the poorly soluble antiretroviral agent, nevirapine. The phase solubility diagram indicates 1:1 stoichiometry and is supported by electronspray ionization mass spectrometry. The complexes were characterized by DSC, FT-IR, and XRD in the solid state. The ternary systems were autoclaved before being lyophilized for the best results. Proton NMR suggests that the methyl pyridine ring of the drug is involved in inclusion and enters from the wider side of the cavity which was confirmed by COESY NMR. Solution calorimetry, a direct method to determine the thermodynamic parameters, was used to determine the complexation constant (K) and other thermodynamic properties. The process is associated with negative ΔH and positive ΔS indicating a stable inclusion complex. The value of K follows the order β-CD < HP-β-CD < M-β-CD. The molar enthalpy of solution in autoclaved solid formulation is les...

Crystal structure and thermochemical properties of 1-decylammonium hydrochloride (C 10H 21NH 3Cl)(s)

The compound 1-decylammonium hydrochloride was synthesized by the method of liquid phase reflux. Chemical analysis, elemental analysis, and X-ray crystallography were applied to characterise its composition and structure. The lattice potential energy of the crystalline solid compound was calculated from data of the crystal structure. The values of the molar enthalpy of dissolution of 1-decylammonium hydrochloride at different concentrations ( m) at T = 298.15 K were measured by means of an isoperibol solution–reaction calorimeter. According to the Pitzer electrolyte solution theory, the molar solution enthalpy of C 10H 21NH 3Cl(s) at infinite dilution ( Δ s H m ∞ ) and Pitzer parameters ( β MX ( 0 ) L and β MX ( 1 ) L ) were obtained. Then the apparent relative molar enthalpy ( Φ L) of the title compound and relative partial molar enthalpies of solvent and solute ( L ¯ 1 and L ¯ 2 ) were calculated, respectively. Hydration heats of the solid compound and its cation were derived from the molar solution enthalpy of the title compound at infinite dilution ( Δ s H m ∞ ) and the lattice potential energy.

Thermochemistry of aqueous pyridine-3-carboxylic acid (nicotinic acid)

The molar enthalpy of solution of solid nicotinic acid (NA) at T = 298.15 K, to give an aqueous solution of molality m = 3.748 · 10 −3 mol · kg −1, was determined as Δ sol H m = (19,927 ± 48) J · mol −1, by solution calorimetry. Enthalpies of dilution, Δ dil H m , of 0.1005 mol · kg −1 aqueous nicotinic acid to yield final solutions with molality in the approximate range (0.03 to 0.09) mol · kg −1 were also measured by flow calorimetry. Combining the two sets of data and the results of pH measurements, with values of proton dissociation enthalpies and Δ f H m ∘ ( NA, cr ) selected from the literature, it was possible to derive the standard molar enthalpies of formation of the three nicotinic acid species involved in protonation/deprotonation equilibria, at infinite dilution: Δ f H m ∘ ( H N + C 5 H 4 COOH · ∞ H 2 O,aq ) = (328.2 ± 1.2) kJ · mol −1, Δ f H m ∘ ( H N + C 5 H 4 COO - · ∞ H 2 O,aq ) = (325.0 ± 1.2) kJ · mol −1, and Δ f H m ∘ ( NC 5 H 4 COO - · ∞ H 2 O,aq ) = (313.7 ± 1.2) kJ · mol −1. Finally, the enthalpy of solution of nicotinic acid at T = 298.15 K, under saturation conditions ( m = 0.138 mol · kg −1), and the standard molar enthalpy of formation of the corresponding solution could also be obtained as Δ sol H m = (19,773 ± 48) J · mol −1 and Δ f H m ∘ (NA · 402H 2O, aq) = (324.9 ± 1.2) kJ · mol −1, respectively.

Hydrothermal synthesis and thermochemistry of metalloborophosphate of Na 2[CuB 3P 2O 11(OH)]·0.67H 2O

The pure hydrated metalloborophosphate sample, Na 2[CuB 3P 2O 11(OH)]·0.67H 2O, has been synthesized and characterized by XRD, FT-IR, DTA-TG techniques, and chemical analysis. The molar enthalpies of solution of Na 2[CuB 3P 2O 11(OH)]·0.67H 2O(s) in 1 mol · dm −3 HCl (aq), of Cu(OH) 2 (s) in (HCl + H 3BO 3) (aq), and of NaH 2PO 4·2H 2O (s) in (HCl + H 3BO 3 + Cu(OH) 2) (aq) were measured, respectively. With the incorporation of the previously determined enthalpy of solution of H 3BO 3 (s) in 1 mol · dm −3 HCl (aq), together with the use of the standard molar enthalpies of formation for NaH 2PO 4·2H 2O (s), Cu(OH) 2 (s), H 3BO 3 (s), and H 2O (l), the standard molar enthalpy of formation of −(4988.4 ± 2.5) kJ · mol −1 for Na 2[CuB 3P 2O 11(OH)]·0.67H 2O at T = 298.15 K was obtained on the basis of the appropriate thermochemical cycle.

Determination of standard molar enthalpies of formation for the two lead borates: Pb 4B 10O 19·2.5H 2O and Pb 6B 11O 18(OH) 9

Two pure hydrated lead borates, Pb 4B 10O 19·2.5H 2O and Pb 6B 11O 18(OH) 9, have been synthesized and characterized by XRD, FT-IR, DTA-TG techniques and chemical analysis. The molar enthalpies of solution of Pb 4B 10O 19·2.5H 2O and Pb 6B 11O 18(OH) 9 in 1 mol dm −3 HNO 3(aq) were measured to be −51.44 ± 0.18 kJ mol −1 and −91.70 ± 0.19 kJ mol −1, respectively. With the incorporation of the previously determined enthalpies of solution of H 3BO 3(s) in 1 mol dm −3 HNO 3(aq) and of PbO(s) in (HNO 3 + H 3BO 3)(aq), together with the use of the standard molar enthalpies of formation for PbO(s), H 3BO 3(s) and H 2O(l), the standard molar enthalpies of formation of −8231.4 ± 8.6 kJ mol −1 for Pb 4B 10O 19·2.5H 2O and −9967.5 ± 9.8 kJ mol −1 for Pb 6B 11O 18·4.5H 2O were obtained on the basis of the appropriate thermochemical cycles.

Enthalpy of Solvation of Monoglyme, Diglyme, Triglyme, Tetraglyme, and Pentaglyme in Mixtures of Water with N,N-Dimethylformamide at 298.15 K

The standard molar enthalpies of solution of linear polyethers (LPs) such as 1,2-dimethoxyethane (monoglyme), diethyleneglycol dimethyl ether (diglyme), triethyleneglycol dimethyl ether (triglyme), tetraethyleneglycol dimethyl ether (tetraglyme), and pentaethyleneglycol dimethyl ether (pentaglyme) in a mixture of water and N,N-dimethylformamide were measured at a temperature of 298.15 K. The values of standard molar enthalpy of solution, ΔsolHmo, the enthalpic effect of hydrophobic hydration, Hb(H2O), and the enthalpic effect of cyclization of these glymes have been determined. The values of standard molar enthalpy of solution of LPs are more negative than those of their cyclic equivalents. The exothermic enthalpic effect of hydrophobic hydration of LPs increases linearly with the increase in the number of −CH2− groups. The values of the standard molar enthalpy of solution and the enthalpic effect of hydrophobic hydration of LPs calculated in this paper have been compared to those data for cyclic polyethers (CPs) obtained earlier. The contributions of particular groups (−CH2−, −O−, and −CH3) to the enthalpic effect of hydrophobic hydration have been calculated.

Effect of Temperature on the Process of Hydrophobic Hydration. Part II. Hydrophobic Hydration of 15-Crown-5 and 18-Crown-6 Ethers

The dissolution enthalpy of 1,4,7,10,13-pentaoxacyclopentadecane (15-crown-5) and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) ethers in the mixture of water and N,N-dimethylformamide (DMF) was measured within the range from (293.15 to 308.15) K. The values of standard molar enthalpies of solution, ΔsolHmo, of crown ethers: 15-crown-5 and 18-crown-6 in the mixture of water and N,N-dimethylformamide within the range of the mixture composition under investigation, increase linearly with increasing temperature. The values of partial molar heat capacity, Cp,2o, and hydrophobic hydration effect, Hb(H2O), were determined. The effect of temperature on the process of hydrophobic hydration of crown ethers has been interpreted. The values of the enthalpic effect of hydrophobic hydration are more negative for 18-crown-6 than those for 15-crown-5. The exothermic enthalpic effect of hydrophobic hydration, Hb(H2O), of the crown ethers under investigation decreases linearly with increasing temperature.

Thermochemistry of two lead borates; Pb(BO 2) 2·H 2O and PbB 4O 7·4H 2O

Two pure hydrated lead borates, Pb(BO 2) 2·H 2O and PbB 4O 7·4H 2O, have been characterized by XRD, FT-IR, DTA-TG techniques and chemical analysis. The molar enthalpies of solution of Pb(BO 2) 2·H 2O and PbB 4O 7·4H 2O in 1 mol dm −3 HNO 3(aq) were measured to be (−35.00 ± 0.18) kJ mol −1 and (35.37 ± 0.14) kJ mol −1, respectively. The molar enthalpy of solution of H 3BO 3(s) in 1 mol dm −3 HNO 3(aq) was measured to be (21.19 ± 0.18) kJ mol −1. The molar enthalpy of solution of PbO(s) in (HNO 3 + H 3BO 3)(aq) was measured to be −(61.84 ± 0.10) kJ mol −1. From these data and with incorporation of the enthalpies of formation of PbO(s), H 3BO 3(s) and H 2O(l), the standard molar enthalpies of formation of −(1820.5 ± 1.8) kJ mol −1 for Pb(BO 2) 2·H 2O and −(4038.1 ± 3.4) kJ mol −1 for PbB 4O 7·4H 2O were obtained on the basis of the appropriate thermochemical cycles.

Phase Equilibrium in the System RbCl−NdCl3−HCl(13.26 %)−H2O at 298.15 K and Standard Molar Enthalpy of Formation of New Solid Phase Compound

The solubility of the quaternary system RbCl−NdCl3−HCl(13.26 %)−H2O at 298.15 K was determined, and the corresponding equilibrium diagram was constructed. The quaternary system consists of three equilibrium solid phases, RbCl, RbNdCl4·4H2O (1:1 type), and NdCl3·6H2O. The new solid phase compound RbNdCl4·4H2O was found to be congruently soluble in the system. The compound RbNdCl4·4H2O was characterized by X-ray diffraction, X-ray diffraction single crystal structure analysis, thermogravimetry, and differential thermogravimetry. It belongs to an orthorhombic system, with space group P21212, a = 0.6986(6) nm, b = 1.1319(1) nm, c = 0.6665(6) nm, Dc = 2.795 g·cm−3, and Z = 2. The compound loses its crystal water by one step at (370 to 474) K. The standard molar enthalpy of solution of RbNdCl4·4H2O in deionized water was measured to be −(26.97 ± 0.24) kJ·mol−1 by heat conduction microcalorimetry. Its standard molar enthalpy of formation was calculated to be −(2732.3 ± 1.0) kJ·mol−1.

ChemInform Abstract: The Standard Molar Enthalpy of Formation of ThMo2O8

Abstract The molar enthalpies of solution of ThMo 2 O 8 , Mo, and ThF 4 in (10 mol dm −3 HF(aq) + 4.41 mol dm −3 H 2 O 2 (aq)) have been measured using an isoperibol calorimeter. From these results and other auxiliary data, the standard molar enthalpy of formation of ThMo 2 O 8 has been calculated to be Δ f H m 0 (298.15 K) = (−2742.2 ± 4.5) kJ mol −1 . This value of enthalpy of formation of ThMo 2 O 8 is consistent with the second law enthalpy of formation of ThMo 2 O 8 determined in this laboratory by transpiration technique.

The Estimation of Standard Molar Enthalpies of Solution for VOSO4⋅nH2O(s) in Water and in Aqueous H2SO4

The molar enthalpies of solution of VOSO4⋅3.52H2O(s) at various molalities in water and in aqueous sulfuric acid (0.1 mol⋅kg−1), ΔsolHm, were measured by a solution-reaction isoperibol calorimeter at 298.15±0.01 K. An improved Archer’s method to estimate the standard molar enthalpy of solution, \(\Delta_{\mathrm{sol}}H^{0}_{\mathrm{m}}\), was put forward. In terms of the improved method, the values of \(\Delta_{\mathrm{sol}}H^{0}_{\mathrm{m}}=-24.12\pm 0.03~\mbox{kJ}{\cdot}\mbox{mol}^{-1}\) of VOSO4⋅3.52H2O(s) in water and \(\Delta_{\mathrm{sol}}H^{0}_{\mathrm{m}}=-15.38\pm 0.06~\mbox{kJ}{\cdot}\mbox{mol}^{-1}\) in aqueous sulfuric acid were obtained, respectively. The data indicates that the energy state of VOSO4 in aqueous H2SO4 is higher than that in pure water.