Temperature Dependence Of Vapor Pressure Research Articles

Benchmark Thermodynamic Properties of Methyl- and Methoxybenzamides: Comprehensive Experimental and Theoretical Study.

The enthalpies of formation of 2-, 3-, and 4-CH3-benzamide, as well as for 2-CH3O-benzamide, were measured by using combustion calorimetry. Vapor pressures of the isomeric CH3- and CH3O-benzamides were measured by using the transpiration method. The enthalpies of sublimation/vaporization of these compounds at 298 K were obtained from temperature dependencies of vapor pressures. The enthalpies of solution of the isomeric CH3- and CH3O-benzamides were measured with solution calorimetry. The enthalpies of sublimation of m- and p-substituted benzamides were independently derived with help of a solution calorimetry-based procedure. The enthalpies of fusion of the CH3-benzamides were derived from differential scanning calorimetry measurements. Thermochemical data on CH3- and CH3O-benzamides were collected, evaluated, and tested for internal consistency. A simple incremental procedure was suggested for a quick appraisal of vaporization enthalpies of substituted benzamides. The high-level G4 quantum-chemical method was used for mutual validation of the experimental and theoretical gas-phase enthalpies of formation. A remarkable ability of the G4-based atomization procedure to calculate reliable enthalpies of formation was established for the set of aliphatic and aromatic amides. An outlook for the proper validation of the G4-AT procedure was discussed.

Synthesis, structure, vapour pressure and deposition of ZnO thin film by plasma assisted MOCVD technique using a novel precursor bis[(pentylnitrilomethylidine) (pentylnitrilomethylidine-μ-phenalato)]dizinc(II)

A novel binuclear zinc schiff's base complex bis[(pentylnitrilomethylidine)(pentylnitrilomethylidine-μ-phenalato)]dizinc(II) (hereafter referred as ZSP) was prepared and used as a precursor for the deposition of ZnO thin film by MOCVD. The dynamic TG run of ZSP showed sufficient volatility and good thermal stability. The temperature dependence of vapour pressure measured by transpiration technique yielded a value of 55.8 ± 2.3 kJ mol−1 for the enthalpy of sublimation (ΔH°sub) in the temperature range of 423–503 K. The crystal structure of ZSP was solved by single crystal XRD which exhibits triclinic crystal system with the space group of Pī. The molecular mass of ZSP was determined by mass spectrometry which yielded the m/z value of 891 and 445 Da corresponding to its dimeric as well as monomeric form. The complex ZSP was further characterized by FT-IR and NMR. The demonstration of ZnO thin film deposition was carried out by using plasma assisted MOCVD. The thin film XRD confirmed the highly oriented (002) ZnO thin films on Si(100) substrate. The uniformity and composition of the thin film were analyzed by SEM/EDX. The band gap of ZnO thin film measurement indicated the blue shift with the value of 3.79 eV.

Temperature-Dependent Oxygen Effect on NMR D-[Formula: see text] Relaxation-Diffusion Correlation of n-Alkanes.

Nuclear magnetic resonance (NMR) diffusion-relaxation correlation experiments (D-T_2) are widely used for the petrophysical characterisation of rocks saturated with petroleum fluids both in situ and for laboratory analyses. The encoding for both diffusion and relaxation offers increased fluid typing contrast by discriminating fluids based on their self-diffusion coefficients, while relaxation times provide information about the interaction of solid and fluid phases and associated confinement geometry (if NMR responses of pure fluids at particular temperature and pressure are known). Petrophysical interpretation of D-T_2 correlation maps is typically assisted by the “standard alkane line”—a relaxation-diffusion correlation valid for pure normal alkanes and their mixtures in the absence of restrictions to diffusing molecules and effects of internal gradients. This correlation assumes fluids are free from paramagnetic impurities. In situations where fluid samples cannot be maintained at air-free state the diffusion-relaxation response of fluids shift towards shorter relaxation times due to oxygen paramagnetic relaxation enhancement. Interpretation of such a response using the “standard alkane line” would be erroneous and is further complicated by the temperature-dependence of oxygen solubility for each component of the alkane mixture. We propose a diffusion-relaxation correlation suitable for interpretation of low-field NMR D-T_2 responses of normal alkanes and their mixtures saturating rocks over a broad temperature range, in equilibrium with atmospheric air. We review and where necessary revise existing viscosity-relaxation correlations. Findings are applied to diffusion-relaxation dependencies taking into account the temperature dependence of oxygen solubility and solvent vapour pressure. The effect is demonstrated on a partially saturated carbonate rock.

CO2 absorption, density, viscosity and vapor pressure of aqueous potassium carbonate+2-methylpiperazine

The physical properties of the absorbent are important for designing a CO2 capture process. The density and viscosity are used to calculate the mass transfer coefficient that determines the height of the absorber. Furthermore, these physical data affect the selection of liquid pump and pipe lines. Vapor pressure is a factor that estimates absorbent loss and condenser size. In this study, the physical properties of the aqueous potassium carbonate (K2CO3)+2-methylpiperazine (2MPZ) solution were obtained in a temperature range from 303.15 K to 343.15 K. The physical properties of the different aqueous K2CO3+2MPZ solutions (various amine concentrations and amounts of CO2 absorbed) were measured to obtain the parameters for process design. A regression analysis was conducted for the experimental data. The densities of the aqueous K2CO3+2MPZ solutions increased when the amounts of absorbed CO2 or 2MPZ concentrations were increased. The densities and viscosities of the absorbents decreased according to the increase in temperature. The viscosities of the absorbent increased when 2MPZ concentrations were increased. The temperature dependency of vapor pressure follows the Antoine equation; the CO2 gas and aqueous solution of a base follows the vapor pressure variation of the mixed solution.

Nicotinamides: Evaluation of thermochemical experimental properties

Vapor pressures of the isomeric 2-, 3-, and 4-pyridinecarboxamides were measured by using the transpiration method. The enthalpies of sublimation/vaporization of these compounds at 298.15K were derived from vapor pressure temperature dependences. The enthalpies of solution of the isomeric pyridinecarboxamides were measured with the high-precision solution calorimetry. The enthalpies of sublimation of 3- and 4-pyridinecarboxamides were independently derived with help of the solution calorimetry based procedure. The enthalpies of fusion of the pyridinecarboxamides were measured by the DSC. Thermochemical data isomeric pyridinecarboxamides were collected, evaluated, and tested for internal consistency. The high-level G4 quantum-chemical method was used for mutual validation of the experimental and theoretical gas phase enthalpies of formation successfully.

Visualizing Vapor Pressure: A Mechanical Demonstration of Liquid–Vapor Phase Equilibrium

Abstract Water phase transitions are central to climate and weather. Yet it is a common experience that the principles of phase equilibrium are challenging to understand and teach. A simple mechanical analogy has been developed to demonstrate key principles of liquid evaporation and the temperature dependence of equilibrium vapor pressure. The system is composed of a circular plate with a central depression and several hundred metal balls. Mechanical agitation of the plate causes the balls to bounce and interact in much the same statistical way that molecules do in real liquid–vapor systems. The data, consisting of the number of balls escaping the central well at different forcing energies, exhibit a logarithmic dependence on the reciprocal of the applied energy (analogous to thermal energy kBT) that is similar to that given by Boltzmann statistics and the Clausius–Clapeyron equation. These results demonstrate that the enthalpy (i.e., latent heat) of evaporation is well interpreted as the potential energy difference between molecules in the vapor and liquid phases, and it is the fundamental driver of vapor pressure increase with temperature. Consideration of the uncertainties in the measurements shows that the mechanical system is described well by Poisson statistics. The system is simple enough that it can be duplicated for qualitative use in atmospheric science teaching, and an interactive animation based on the mechanical system is available online for instructional use (http://phy.mtu.edu/vpt/).

Structure–property relationships in halogenbenzoic acids: Thermodynamics of sublimation, fusion, vaporization and solubility

Temperature dependences of vapor pressures for 2-, 3-, and 4-bromobenzoic acid, as well as for five isomeric bromo-methylbenzoic acids were studied by the transpiration method. Melting temperatures and enthalpies of fusion for all isomeric bromo-methylbenzoic acids and 4-bromobenzoic acid were measured with a DSC. The molar enthalpies of sublimation and vaporization were derived. These data together with results available in the literature were collected and checked for internal consistency using a group-additivity procedure and results from X-ray structural diffraction studies. Specific (hydrogen bonding) interactions in the liquid and in the crystal phase of halogenbenzoic acids were quantified based on experimental values of vaporization and sublimation enthalpies. Structure-property correlations of solubilities of halogenobenzoic acids with sublimation pressures and sublimation enthalpies were developed and solubilities of bromo-benzoic acids were estimated. These new results resolve much of the ambiguity in the available thermochemical and solubility data on bromobenzoic acids. The approach based on structure property correlations can be applied for the assessment of water solubility of sparingly soluble drugs.

Six-membered ring aliphatic compounds: A search for regularities in phase transitions

Absolute vapor pressures of 1-Cl-adamantane, 2-Cl-adamantane, 1-Br-adamantane, 2-Br-adamantane, as well as of Br-cyclohexane were measured by using the transpiration method. Standard molar enthalpies of sublimation of halogen substituted adamantanes at 298.15K were derived from vapor pressure temperature dependences. Standard molar enthalpies of solution of adamantane and halogen adamantanes in cyclohexane were measured with a high-precision solution calorimeter. A theoretical procedure based on the solution calorimetry was applied to derive sublimation enthalpies of halogen adamantanes independently. Molar enthalpies of fusion were measured with help of DSC. The consistent data set of phase transitions for each compound was evaluated and used for discussion of structure-property relations in adamantane and cyclohexane derivatives. A simple way to predict enthalpies of vaporization of compounds containing six-membered rings was suggested for practical thermochemical calculations.

Thermal properties of some organosilicon precursors for chemical vapor deposition

Five volatile organosilicon compounds: trimethyl(phenyl)silane Me3SiC6H5 (I), trimethyl(cyclohexyl)silane Me3SiC6H11 (II), trimethyl(phenoxy)silane Me3SiOC6H5 (III), trimethyl(cyclohexyloxy)silane Me3SiOC6H11 (IV), and trimethyl(allyloxy)silane Me3SiOC3H5 (V) were synthesized, purified, and identified. Data of IR spectroscopy; gas–liquid chromatography; and 1H NMR, 13C NMR, 29Si NMR analyses were used to identify and confirm the high purity of the compounds (more than 99.6 %). The thermal stability of the compounds was investigated by DTA-TG. The quantitative data on temperature dependences of the saturated vapor pressure of the compounds were obtained by static tensimetry method with glass membrane null manometer. The volatilities of compounds Me3SiOC6H5, Me3SiC6H5, Me3SiC6H11, Me3SiOC6H11 were shown to be close due to the presence of large-size phenyl/cyclohexyl group. The replacement of phenyl/cyclohexyl group by allyl substituent in the molecule led to significant increase in volatility for Me3SiOC3H5 in comparison with compounds mentioned before. The vapor pressure of all of the compounds is enough to use them as precursors in CVD processes without additional heating. The thermodynamic parameters (enthalpies and entropies) of vaporization processes for four compounds II–V were determined for the first time.

Thermodynamic study of sublimation, melting and vaporization of scandium(III) dipivaloylmethanate derivatives

The present work deals with the investigation of thermal properties of two volatile scandium(III) beta-diketonates with 2,2,6,6-tetramethyl-4-fluoro-3,5-heptanedione and 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione which have been synthesized and purified. Using the static method with glass membrane gauge-manometer the temperature dependencies of saturated and unsaturated vapor pressure were measured for the first time. The temperatures and enthalpies of melting were measured for these compounds by differential scanning calorimetry. The standard thermodynamic characteristics of enthalpy and entropy for sublimation, vaporization and melting processes were derived.

Thermodynamic study on six tricyclic nitrogen heterocyclic compounds by thermal analysis and effusion techniques

The molar sublimation and vaporization enthalpies of acridine, phenanthridine, 1,7-phenanthroline, 1,10-phenanthroline, 4,7-phenanthroline and phenazine were determined at the averages of their respective experimental temperature ranges (ΔcrgH0m (<T>) and ΔlgH0m (<T>), respectively) from the temperature dependencies of vapor pressure determined using Knudsen Effusion Mass Loss (KEML), Torsion Effusion (TE) and Isothermal Thermogravimetry (ITG) above their solid and liquid phases. The fusion characteristics (melting temperatures and the molar standard enthalpies of fusion at their melting temperatures) measured by Differential Scanning Calorimetry (DSC) were compared with the available literature values. Solid and liquid vapor pressure data determined by KEML, TE and ITG techniques as well as ΔcrgH0m (<T>) and ΔlgH0m (<T>) values, adjusted at 298.15K by using the values of Cp(cr) and Cp(l) calculated by a well-known group additivity method, were found to be fairly correlated and are consistent with the available literature data. Final ΔcrgH0m(298.15K) values were also provided as weighted averages of all the available data.

Temperature dependences of saturated vapor pressure and the enthalpy of vaporization of n-pentyl esters of dicarboxylic acids

The saturated vapor pressures and enthalpies of vaporization of n-pentyl esters of linear С2–С6 dicarboxylic acids are determined by the transpiration method in the temperature range of 309.2–361.2 K. The dependences of enthalpies of vaporization on the number of carbon atoms in the molecule and on the retention indices have been determined. The predictive capabilities of the existing calculation schemes for estimation of enthalpy of vaporization of the studied compounds have been analyzed.

Alumazene adducts with acetonitrile: Structure and thermal stability

Lewis acid-base adducts of the “inorganic analog of benzene” alumazene [{2,6-(i-Pr)2C6H3NAlMe}3] (1) with acetonitrile (CH3CN, acn) and deuteroacetonitrile (CD3CN, d3-acn) were synthesized, spectroscopically characterized, and their molecular structures were elucidated by the X-ray diffraction analysis as a bis-adduct 1(acn)2 and a tris-adduct 1(d3-acn)3. The thermodynamics of complex formation was investigated experimentally and theoretically. Thermodynamic characteristics of process 1(acn)3·acn (s) = 1(acn)2 (s) + 2 acn (g) in the temperature range 294–370 K have been derived from the vapor pressure–temperature dependence measurements by the static tensimetric method. It is shown that above 435 K in the presence of 1 gaseous acn undergoes irreversible polymerization reaction. Quantum chemical computations at B3LYP/6-311G(d,p) level of theory have been performed for the 1(acn)n and model complexes of [(HAlNH)3] (1m), 1m(acn)n (n = 1–3). Obtained results indicate that for the gas phase adducts upon increasing the number of acn ligands the donor-acceptor Al–N(acn) distances increase in accord with decrease of the donor-acceptor bond dissociation energies.

Synthesis and crystal structure of cobalt(II) Schiff base precursor for cobalt oxide thin film by thermal chemical vapor deposition

The tetrahedral Schiff base complex bis(N-isopropylsalicylaldimine)cobalt(II) [Co(saliprn)2] (CSI) was prepared by template method. The complex was characterized by FT-IR, mass spectroscopy, TG/DTA and single crystal X-ray structure determination analysis. The dynamic TG analysis showed that the complex is completely volatile. The equilibrium vapor pressure of the complex was studied by non-isothermal and isothermal thermogravimetric transpiration techniques over the temperature range of 474–514K. The Ea (48.4kJmol−1) and ΔHsub (111.54kJmol−1) for the complex and expression for temperature dependence of vapor pressure (Pe) were obtained. The thermal behavior of the cobalt(II) complex was studied by thermogravimetry techniques using different non-isothermal heating rates under nitrogen atmosphere. The complex was found to be volatile and used in thermal chemical vapor deposition for the development of nanocrystalline cobalt oxide thin films over silica substrates. These nanocrystalline thin films were analyzed by XRD and SEM confirmed the presence of Co3O4 phase with almost nil carbon.

Predicting Flash Points of Pure Compounds and Mixtures with COSMO-RS

Flash point (FP) is an important parameter for assessing the safety of chemical compounds. Many empirical approaches have been developed to predict FPs based on molecular structure, sometimes involving a large number of descriptors and resulting in class-specific equations. We demonstrate in this work that a satisfying and rather general prediction of the saturation pressure at the FP can be achieved using only the molecular surface area. This relation in combination with any experimental or computational method for calculating temperature-dependent vapor pressures thus allows for the prediction of the FP. In a second step, we calculate the FPs of mixtures using COSMO-RS activity coefficients. By using the proposed method, we were able to calculate flash points without the need for data typically generated in experiments such as normal boiling points or enthalpies of combustion, although experimental pure-compound FPs and vapor-pressure data still can be used to increase the prediction quality.

Thermodynamic properties of 5(nitrophenyl) furan-2-carbaldehyde isomers.

BackgroundThe aim of the current work was to determine thermo dynamical properties of 5(2-nitro phenyl)-furan-2-carbaldehyde, 5(3-nitro phenyl)-furan-2-carbaldehyde and 5(4-nitro phenyl)-furan-2-carbaldehyde.ResultsThe temperature dependence of saturated vapor pressure of 5(2-nitro phenyl)-furan-2-carbaldehyde, 5(3-nitro phenyl)-furan-2-carbaldehyde and 5(4-nitro phenyl)-furan-2-carbaldehyde was determined by Knudsen’s effusion method. The results are presented by the Clapeyron–Clausius equation in linear form, and via this form, the standard enthalpies, entropies and Gibbs energies of sublimation and evaporation of compounds were calculated at 298.15 K. The standard molar formation enthalpies of compounds in crystalline state at 298.15 K were determined indirectly by the corresponding standard molar combustion enthalpy, obtained using bomb calorimetry combustion.ConclusionsDetermination of the thermodynamic properties for these compounds may contribute to solving practical problems pertaining optimization processes of their synthesis, purification and application and it will also provide a more thorough insight regarding the theoretical knowledge of their nature.Graphical abstract:Generalized structural formula of investigated compounds and their formation enthalpy determination scheme in the gaseous state

Studying the sublimation thermodynamics of ethionamide and pyridinecarbothioamide isomers by transpiration method

Temperature dependences of saturated vapor pressure for crystalline phases of 2-ethyl-4-pyridinecarbothioamide (ethionamide) and two parent compounds 2- and 4-pyridinecarbothioamide isomers were measured by the transpiration method. The results were used to determine the standard molar enthalpies, entropies and Gibbs energies of sublimation at T=298.15K. HYBOT descriptors application has shown an increase in the donor–acceptor ability of the molecules of the studied compounds to form hydrogen bonds to result in their crystal lattice energy growth. The obtained standard molar sublimation enthalpies have been compared with the literature results for 2- and 4-substituted pyridine isomers.

Building Blocks for Ionic Liquids: Vapor Pressures and Vaporization Enthalpies of N-Functionalized Imidazoles with Branched and Cycloalkyl Substituents

The imidazole structure offers a versatile means of developing molecules with controlled/tunable physicochemical properties that have significant utility in many applications and can be further derivatized to form ionic liquids. In the literature, the vast majority of studies on structure–property relationships in these types of molecules are devoted to linear (e.g., n-alkyl) substituents. However, imidazoles with branched or cycloalkyl groups are equally accessible through convenient synthetic methods – yet there are essentially no reports on the physical properties of such compounds in the literature. Here, the absolute vapor pressures of branched and cycloalkyl derivatives of imidazole have been determined as a function of temperature by the transpiration method. The standard molar enthalpies of vaporization were derived from the temperature dependences of vapor pressures. The measured data sets were successfully checked for internal consistency by comparison with vaporization enthalpies of the parent ...

Benchmark Thermochemistry for Biologically Relevant Adenine and Cytosine. A Combined Experimental and Theoretical Study.

The thermochemical properties available in the literature for adenine and cytosine are in disarray. A new condensed phase standard (p° = 0.1 MPa) molar enthalpy of formation at T = 298.15 K was measured by using combustion calorimetry. New molar enthalpies of sublimation were derived from the temperature dependence of vapor pressure measured by transpiration and by the quarz-crystal microbalance technique. The heat capacities of crystalline adenine and cytosine were measured by temperature-modulated DSC. Thermodynamic data on adenine and cytosine available in the literature were collected, evaluated, and combined with our experimental results. Thus, the evaluated collection of data together with the new experimental results reported here has helped to resolve contradictions in the available enthalpies of formation. A set of reliable thermochemical data is recommended for adenine and cytosine for further thermochemical calculations. Quantum-chemical calculations of the gas phase molar enthalpies of formation of adenine and cytosine have been performed by using the G4 method and results were in excellent agreement with the recommended experimental data. The standard molar entropies of formation and the standard molar Gibbs functions of formation in crystal and gas state have been calculated. Experimental vapor-pressure data measured in this work were used to estimate pure-component PC-SAFT parameters. This allowed modeling solubility of adenine and cytosine in water over the temperature interval 278-310 K.

Thermodynamic properties of isomeric iso-butoxybenzoic acids: Experimental and theoretical study

Standard (p°=0.1MPa) molar enthalpies of formation at the temperature T=298.15K of the 2-, 3-, and 4-iso-butoxybenzoic acids were measured using the combustion calorimetry. Standard molar enthalpies of vaporization and sublimation were derived from the vapor pressure temperature dependencies measured by the transpiration method. Molar enthalpies of the solid state phase transitions were measured by the DSC. Thermodynamic data on alkoxy substituted benzoic acids available in the literature were collected and combined with own experimental results. This data set on alkoxybenzoic acids was evaluated by using quantum-chemical and group-additivity methods.