The Experts below are selected from a list of 1428 Experts worldwide ranked by ideXlab platform

Manuel Ribeiro A V Da Silva - One of the best experts on this subject based on the ideXlab platform.

  • structural studies of cyclic ureas 3 Enthalpy of formation of barbital
    The Journal of Chemical Thermodynamics, 2009
    Co-Authors: Maria Ribeiro D M C Da Silva, Manuel Ribeiro A V Da Silva, Vera L.s. Freitas, Maria Victoria Roux, Pilar Jimenez, Manuel Temprado, Juan Z Davalos, Pilar Cabildo, Rosa M Claramunt, Jose Elguero
    Abstract:

    Abstract A thermochemical and thermophysical study has been carried out for crystalline barbital [5,5′-diethylbarbituric acid]. The thermochemical study was made by static bomb combustion calorimetry, from which the standard ( p ∘ = 0.1 MPa ) molar Enthalpy of formation of the crystalline barbital, at T = 298.15 K, was derived as −(753.0 ± 1.8) kJ · mol−1. The thermophysical study was made by differential scanning calorimetry over the temperature interval (265 to 470) K. A solid–solid phase transition was found at T = 413.3 K. The vapour pressures of the crystalline barbital were measured at several temperatures between T = (355 and 377) K, by the Knudsen mass-loss effusion technique, from which the standard molar Enthalpy of Sublimation, at T = 298.15 K was derived as (117.3 ± 0.6) kJ · mol−1. The combination of the experimental results yielded the standard molar Enthalpy of formation of barbital in the gaseous phase, at T = 298.15 K, as −(635.8 ± 1.9) kJ · mol−1. This value is compared and discussed with our theoretical calculations by several methods (Gaussian-n theories G2 and G3, complete basis set CBS-QB3, density functional B3P86 and B3LYP) by means of atomization and isodesmic reaction schemes.

  • measurement of enthalpies of Sublimation by drop method in a calvet type calorimeter design and test of a new system
    Thermochimica Acta, 2004
    Co-Authors: Luis M N B F Santos, Bernd Schroder, Óscar O. P. Fernandes, Manuel Ribeiro A V Da Silva
    Abstract:

    Abstract A new system to measure enthalpies of Sublimation by the drop method was designed, constructed and tested. The performance of the apparatus was checked by measuring the Enthalpy of Sublimation of ferrocene, benzoic acid and anthracene at different temperatures. The measurement of enthalpies of Sublimation by the drop method is described in detail. Compound 〈 T exp 〉 (K) 〈 Δ cr g H m ∘ 〉 (kJ mol −1 ) Benzoic acid 417 92.1 ± 2.6 Benzoic acid 453 93.9 ± 3.1 Ferrocene 373 74.9 ± 1.7 Anthracene 453 100.8 ± 1.7

  • standard molar Enthalpy of formation vapour pressures and standard molar Enthalpy of Sublimation of benzanthrone
    The Journal of Chemical Thermodynamics, 1999
    Co-Authors: Manuel Ribeiro A V Da Silva, Manuel J.s. Monte, Jorge M Goncalves, Luisa M C C H Ferrao, Fang Jiye
    Abstract:

    Abstract The standard ( p o  =  0.1 MPa) molar Enthalpy of combustion at T  =  298.15 K of crystalline benzanthrone was determined as Δ c H m o  =  − (8114.7  ±  2.0) kJ · mol  − 1 by static-bomb calorimetry, and the standard molar Enthalpy of formation of the crystal at T  =  298.15 K was derived as Δ f H m o ( cr )  =  − (4.1  ±  3.0) kJ · mol  − 1 . Vapour pressure as a function of temperature was measured using the mass-loss Knudsen effusion technique, from which the standard molar Enthalpy of Sublimation at T  =  298.15 K was derived as Δ cr g H m o  =  (126.6  ±  0.6) kJ · mol  − 1 . The standard molar Enthalpy of Sublimation at T  =  298.15 K was also measured by the quartz oscillator method, Δ cr g H m o  =  (129.7  ±  2.1) kJ · mol  − 1 .

  • Enthalpy of Sublimation of bis pentane 2 4 dionato copper ii
    The Journal of Chemical Thermodynamics, 1994
    Co-Authors: Manuel Ribeiro A V Da Silva, Luisa M C C H Ferrao
    Abstract:

    Abstract The standard ( p o = 0.1 MPa) molar Enthalpy of Sublimation of bis(pentane-2,4-dionato)-copper(II) has been redetermined, at the temperature T = 451 K, by the “Skinner vacuumSublimation technique” using a high-temperature microcalorimeter, from which the value at T = 298.15 K has been derived as Δ cr 8 H m o (298.15K) = (116.6 ± 2.0) kJ · mol −1 .

  • the Enthalpy of Sublimation of diphenylacetylene from knudsen effusion studies
    Thermochimica Acta, 1993
    Co-Authors: Herminio P Diogo, Manuel Ribeiro A V Da Silva, Manuel Minas E Da Piedade, Anabela C Fernandes, Jose Martinho A Simoes, Manuel J.s. Monte
    Abstract:

    The Enthalpy of Sublimation of diphenylacetylene at 298.15 K, ΔgcrH⊖m(C2(C6H5)2] = 95.1 ± 1.1 kJmol−1, was derived from vapour pressure-temperature data, obtained with two different Knudsen effusion apparatus, and from heat capacity measurements obtained by differential scanning calorimetry. The molybdenum-diphenylacetylene bond dissociation Enthalpy in Mo(η5-C5H5)2[C2(C6H5)2] was reevaluated as 115 ± 26 kJ mol−1, on the basis of the new value for ΔcrgH⊖m[C2(C6H5)2].

Manuel J.s. Monte - One of the best experts on this subject based on the ideXlab platform.

  • Energetic studies and phase diagram of thioxanthene.
    Journal of Physical Chemistry A, 2009
    Co-Authors: Vera L.s. Freitas, Manuel J.s. Monte, José R. B. Gomes, Luis M N B F Santos, Maria D.m.c. Ribeiro Da Silva
    Abstract:

    The molecular stability of thioxanthene, a key species from which very important compounds with industrial relevance are derived, has been studied by a combination of several experimental techniques and computational approaches. The standard (p° = 0.1 MPa) molar Enthalpy of formation of crystalline thioxanthene (117.4 ± 4.1 kJ·mol−1) was determined from the experimental standard molar energy of combustion, in oxygen, measured by rotating-bomb combustion calorimetry at T = 298.15 K. The Enthalpy of Sublimation was determined by a direct method, using the vacuum drop microcalorimetric technique, and also by an indirect method, using a static apparatus, where the vapor pressures at different temperatures were measured. The latter technique was used for both crystalline and undercooled liquid samples, and the phase diagram of thioxanthene near the triple point was obtained (triple point coordinates T = 402.71 K and p = 144.7 Pa). From the two methods, a mean value for the standard (p° = 0.1 MPa) molar enthalp...

  • new static apparatus and vapor pressure of reference materials naphthalene benzoic acid benzophenone and ferrocene
    Journal of Chemical & Engineering Data, 2006
    Co-Authors: Manuel J.s. Monte, Luis M N B F Santos, Michal Fulem, And Jose M S Fonseca, Carlos Sousa
    Abstract:

    A new static apparatus, capable of measuring vapor pressures in the range (0.4 to 133) Pa and in the temperature range (243 to 413) K, is fully described. The performance of the new apparatus was checked by measuring the vapor pressures of four compounds recommended as reference materials for the measurement of vapor pressurenaphthalene, benzoic acid, benzophenone, and ferrocene. A recommended value for the Enthalpy of Sublimation of benzophenone, (298.15 K) = (95.1 ± 1.9) kJ·mol-1, is suggested.

  • standard molar Enthalpy of formation vapour pressures and standard molar Enthalpy of Sublimation of benzanthrone
    The Journal of Chemical Thermodynamics, 1999
    Co-Authors: Manuel Ribeiro A V Da Silva, Manuel J.s. Monte, Jorge M Goncalves, Luisa M C C H Ferrao, Fang Jiye
    Abstract:

    Abstract The standard ( p o  =  0.1 MPa) molar Enthalpy of combustion at T  =  298.15 K of crystalline benzanthrone was determined as Δ c H m o  =  − (8114.7  ±  2.0) kJ · mol  − 1 by static-bomb calorimetry, and the standard molar Enthalpy of formation of the crystal at T  =  298.15 K was derived as Δ f H m o ( cr )  =  − (4.1  ±  3.0) kJ · mol  − 1 . Vapour pressure as a function of temperature was measured using the mass-loss Knudsen effusion technique, from which the standard molar Enthalpy of Sublimation at T  =  298.15 K was derived as Δ cr g H m o  =  (126.6  ±  0.6) kJ · mol  − 1 . The standard molar Enthalpy of Sublimation at T  =  298.15 K was also measured by the quartz oscillator method, Δ cr g H m o  =  (129.7  ±  2.1) kJ · mol  − 1 .

  • the Enthalpy of Sublimation of diphenylacetylene from knudsen effusion studies
    Thermochimica Acta, 1993
    Co-Authors: Herminio P Diogo, Manuel Ribeiro A V Da Silva, Manuel Minas E Da Piedade, Anabela C Fernandes, Jose Martinho A Simoes, Manuel J.s. Monte
    Abstract:

    The Enthalpy of Sublimation of diphenylacetylene at 298.15 K, ΔgcrH⊖m(C2(C6H5)2] = 95.1 ± 1.1 kJmol−1, was derived from vapour pressure-temperature data, obtained with two different Knudsen effusion apparatus, and from heat capacity measurements obtained by differential scanning calorimetry. The molybdenum-diphenylacetylene bond dissociation Enthalpy in Mo(η5-C5H5)2[C2(C6H5)2] was reevaluated as 115 ± 26 kJ mol−1, on the basis of the new value for ΔcrgH⊖m[C2(C6H5)2].

  • standard molar Enthalpy of formation of bis 2 2 6 6 tetramethylheptane 3 5 dionato dioxouranium vi in the crystalline and gaseous states the mean u o bond dissociation Enthalpy
    The Journal of Chemical Thermodynamics, 1993
    Co-Authors: Manuel A.v. Ribeiro Da Silva, Manuel J.s. Monte, Edward Giera, Wladyslaw Kakolowicz
    Abstract:

    Abstract The standard (po = 0.1 MPa) molar Enthalpy of formation, at the temperature 298.15 K, of crystalline bis(2,2,6,6-tetramethylheptane-3,5-dionato) dioxouranium(VI) {uranyl(VI) dipivaloylmethanate, UO2(DPM)2}, was determined by solution-reaction calorimetry as -(2169.9±7.6) kJ·mol-1. The vapour pressure of the crystal, as function of the temperature, was measured using the Knudsen mass-loss effusion technique and the standard molar Enthalpy of Sublimation, at the temperature 298.15 K, was derived as (156.9±1.9) kJ·mol-1. From these results, the standard molar Enthalpy of formation of the complex, in the gaseous state, was derived and the mean uranium(VI)-oxygen bond-dissociation Enthalpy for the binding of the ligand to the metal, 〈D〉(U-O), was calculated as (223±10) kJ·mol-1.

Luis Alfonso Torres - One of the best experts on this subject based on the ideXlab platform.

  • the Enthalpy of Sublimation of 5 10 15 20 tetraphenylporphine and 5 10 15 20 tetrakis 4 methoxyphenyl porphine
    The Journal of Chemical Thermodynamics, 2002
    Co-Authors: Luis Alfonso Torres, Myriam Campos, Esteban Enriquez, Rodrigo Patino
    Abstract:

    Abstract The enthalpies of Sublimation of 5,10,15,20-tetraphenylporphine (CA registry number 917-23-7, TPP) and 5,10,15,20-tetrakis(4-methoxyphenyl)porphine (CA registry number 22112-78-3, TMPP), were determined by the Knudsen effusion method using a quartz-crystal microbalance in a system designed specially to work at high temperatures. The system includes stainless steel-Pyrex glass joints over one of which the effusion cell holder is welded in such a way that the heating and temperature sensor for measurement and control are accessible without venting the system. The design permits precise measurements of the actual sample temperature under low-pressure conditions. From the experimental results the derived values for this property are: Δ cr g H m o (TPP, 550 K)  =  ( 171  ±  2) kJ · mol  − 1 and Δ cr g H m o (TMPP, 563 K)  =  (213  ±  10) kJ · mol  − 1 . Combining these values with the previously reported standard molar enthalpies of formation in the condensed phase, the corresponding standard molar enthalpies of formation in the gas state at T  =  298.15 K were calculated as Δ f H m o (g)  =  (839  ±  9) kJ · mol  − 1 for TPP and Δ f H m o (g)  =  (295  ±  14) kJ · mol  − 1 for TMPP. An estimate of these enthalpies by the second-order Benson’s group additivity approach was computed based upon the assumption of total or null aromaticity in the porphyrin macrocycle. Using the enthalpies of formation of the gaseous atoms in their ground states, the enthalpies of atomisation were derived as: Δ at H m o (g)  =  (39125  ±  22) kJ · mol  − 1 for TPP and Δ at H m o (g)  =  (45277  ±  25) kJ · mol  − 1 for TMPP. Recommended Laidler parameters were used to predict these values, considering a correction for four pyrrole ring strain contribution.

  • a thermochemical study of 5 10 15 20 tetraphenylporphine zinc ii by rotating bomb combustion calorimetry and by knudsen effusion experiments
    The Journal of Chemical Thermodynamics, 2002
    Co-Authors: Rodrigo Patino, Myriam Campos, Luis Alfonso Torres
    Abstract:

    Abstract The standard molar enthalpies of combustion {ΔcHmo(cr)} and formation {ΔfHmo(cr)} at T =  298.15 K ( po =  0.1 MPa) for the 5,10,15,20-tetraphenyl-21H,23H-porphine zinc (ZnTPP, Chemical Abstracts registry number 14074-80-7), were determined by rotating bomb combustion calorimetry. To dissolve the zinc oxides formed during the combustion reaction, an amount of aqueous solution of nitric acid was put into the bomb at the beginning of each experiment; in this way, when the bomb is rotated, a well defined final state is achieved. The corresponding Enthalpy of Sublimation (ΔcrgHmo) at T =  559 K was determined by the Knudsen effusion method using a quartz-crystal microbalance. The derived enthalpies of formation {ΔfHmo(g)} and atomization {ΔatHmo(g)} for gaseous ZnTPP were computed from the experimental measurements. A summary of results ( T =  298.15 K; po =  0.1 MPa) is shown below: With the previously reported Enthalpy of formation value for the free porphyrin, the mean dissociation Enthalpy of the N–Zn co-ordination bond was determined as D(N–Zn)  =  (185  ±  6) kJ · mol − 1in the studied compound.

  • standard reference material proposed for Enthalpy of Sublimation measurements a comparative study of the standard molar Enthalpy of Sublimation of fe c c5h5 2 ferrocene by calorimetry and knudsen effusion techniques
    The Journal of Chemical Thermodynamics, 1995
    Co-Authors: Luis Alfonso Torres, Ramon Gudino, Raphael Sabbah, Juan Antonio Guardado
    Abstract:

    Abstract The standard molar Enthalpy of Sublimation of Fe(c-C5H5)2, bis(η-cyclopentadienyl)iron(II), ferrocene, has been experimentally determined by the Knudsen-effusion method using a quartz-crystal microbalance. The results from two series of experiments were found to be ΔsubH∘m(298.15K) = (74.34 ± 0.41)kJ·mol−1and ΔsubH∘m(280.74K) = (74.60 ± 0.79)kJ·mol−1. This property has also been calorimetrically determined at the temperatureT= 298.15K, and the mean value from 12 experiments were found to be ΔsubH∘m= (73.19 ± 0.66)kJ·mol−1. All the literature results for the standard molar Enthalpy of Sublimation reported to date which have been determined by indirect methods were critically evaluated, and the more reliable values retained. A global analysis including these selected values as well as our effusion and calorimetric results leads to a weighted average value of ΔsubH∘m= (73.42 ± 0.59)kJ·mol−1for the standard molar Enthalpy of Sublimation of Fe(c-C5H5)2atT= 298.15K. From this study we propose the use of ferrocene as a standard reference material for measurements of Enthalpy of Sublimation.

Luisa M C C H Ferrao - One of the best experts on this subject based on the ideXlab platform.

  • standard molar Enthalpy of formation vapour pressures and standard molar Enthalpy of Sublimation of benzanthrone
    The Journal of Chemical Thermodynamics, 1999
    Co-Authors: Manuel Ribeiro A V Da Silva, Manuel J.s. Monte, Jorge M Goncalves, Luisa M C C H Ferrao, Fang Jiye
    Abstract:

    Abstract The standard ( p o  =  0.1 MPa) molar Enthalpy of combustion at T  =  298.15 K of crystalline benzanthrone was determined as Δ c H m o  =  − (8114.7  ±  2.0) kJ · mol  − 1 by static-bomb calorimetry, and the standard molar Enthalpy of formation of the crystal at T  =  298.15 K was derived as Δ f H m o ( cr )  =  − (4.1  ±  3.0) kJ · mol  − 1 . Vapour pressure as a function of temperature was measured using the mass-loss Knudsen effusion technique, from which the standard molar Enthalpy of Sublimation at T  =  298.15 K was derived as Δ cr g H m o  =  (126.6  ±  0.6) kJ · mol  − 1 . The standard molar Enthalpy of Sublimation at T  =  298.15 K was also measured by the quartz oscillator method, Δ cr g H m o  =  (129.7  ±  2.1) kJ · mol  − 1 .

  • Enthalpy of Sublimation of bis pentane 2 4 dionato copper ii
    The Journal of Chemical Thermodynamics, 1994
    Co-Authors: Manuel Ribeiro A V Da Silva, Luisa M C C H Ferrao
    Abstract:

    Abstract The standard ( p o = 0.1 MPa) molar Enthalpy of Sublimation of bis(pentane-2,4-dionato)-copper(II) has been redetermined, at the temperature T = 451 K, by the “Skinner vacuumSublimation technique” using a high-temperature microcalorimeter, from which the value at T = 298.15 K has been derived as Δ cr 8 H m o (298.15K) = (116.6 ± 2.0) kJ · mol −1 .

Rodrigo Patino - One of the best experts on this subject based on the ideXlab platform.

  • the Enthalpy of Sublimation of 5 10 15 20 tetraphenylporphine and 5 10 15 20 tetrakis 4 methoxyphenyl porphine
    The Journal of Chemical Thermodynamics, 2002
    Co-Authors: Luis Alfonso Torres, Myriam Campos, Esteban Enriquez, Rodrigo Patino
    Abstract:

    Abstract The enthalpies of Sublimation of 5,10,15,20-tetraphenylporphine (CA registry number 917-23-7, TPP) and 5,10,15,20-tetrakis(4-methoxyphenyl)porphine (CA registry number 22112-78-3, TMPP), were determined by the Knudsen effusion method using a quartz-crystal microbalance in a system designed specially to work at high temperatures. The system includes stainless steel-Pyrex glass joints over one of which the effusion cell holder is welded in such a way that the heating and temperature sensor for measurement and control are accessible without venting the system. The design permits precise measurements of the actual sample temperature under low-pressure conditions. From the experimental results the derived values for this property are: Δ cr g H m o (TPP, 550 K)  =  ( 171  ±  2) kJ · mol  − 1 and Δ cr g H m o (TMPP, 563 K)  =  (213  ±  10) kJ · mol  − 1 . Combining these values with the previously reported standard molar enthalpies of formation in the condensed phase, the corresponding standard molar enthalpies of formation in the gas state at T  =  298.15 K were calculated as Δ f H m o (g)  =  (839  ±  9) kJ · mol  − 1 for TPP and Δ f H m o (g)  =  (295  ±  14) kJ · mol  − 1 for TMPP. An estimate of these enthalpies by the second-order Benson’s group additivity approach was computed based upon the assumption of total or null aromaticity in the porphyrin macrocycle. Using the enthalpies of formation of the gaseous atoms in their ground states, the enthalpies of atomisation were derived as: Δ at H m o (g)  =  (39125  ±  22) kJ · mol  − 1 for TPP and Δ at H m o (g)  =  (45277  ±  25) kJ · mol  − 1 for TMPP. Recommended Laidler parameters were used to predict these values, considering a correction for four pyrrole ring strain contribution.

  • a thermochemical study of 5 10 15 20 tetraphenylporphine zinc ii by rotating bomb combustion calorimetry and by knudsen effusion experiments
    The Journal of Chemical Thermodynamics, 2002
    Co-Authors: Rodrigo Patino, Myriam Campos, Luis Alfonso Torres
    Abstract:

    Abstract The standard molar enthalpies of combustion {ΔcHmo(cr)} and formation {ΔfHmo(cr)} at T =  298.15 K ( po =  0.1 MPa) for the 5,10,15,20-tetraphenyl-21H,23H-porphine zinc (ZnTPP, Chemical Abstracts registry number 14074-80-7), were determined by rotating bomb combustion calorimetry. To dissolve the zinc oxides formed during the combustion reaction, an amount of aqueous solution of nitric acid was put into the bomb at the beginning of each experiment; in this way, when the bomb is rotated, a well defined final state is achieved. The corresponding Enthalpy of Sublimation (ΔcrgHmo) at T =  559 K was determined by the Knudsen effusion method using a quartz-crystal microbalance. The derived enthalpies of formation {ΔfHmo(g)} and atomization {ΔatHmo(g)} for gaseous ZnTPP were computed from the experimental measurements. A summary of results ( T =  298.15 K; po =  0.1 MPa) is shown below: With the previously reported Enthalpy of formation value for the free porphyrin, the mean dissociation Enthalpy of the N–Zn co-ordination bond was determined as D(N–Zn)  =  (185  ±  6) kJ · mol − 1in the studied compound.