L. Malaspina

Microcalorimetric determination of the enthalpy of sublimation of benzoic acid and anthracene

A Calvet microcalorimeter has been utilized to determine the sublimation enthalpy of benzoic acid and anthracene. The vapor pressures measured by Knudsen effusion weight‐loss method over the temperature ranges 338–383°K and 353–432°K were, respectively, log10p(torr)=(12.175 ± 0.047) − (4501 ± 17)/T, for benzoic acid, and log10p(torr)=(12.616 ± 0.062) − (5277 ± 24)/T, for anthracene. The Gibbs energy functions for C6H5COOH and C14H10 gaseous molecules have been estimated.

Mass Spectrometric Study of the GaAs System

The vaporization of GaAs has been investigated by means of the mass spectrometric method. The activity values of the components were determined in a composition range of 50–95 at.% Ga at 1283°K. The heteronuclear gaseous species GaAs was detected by the aid of double‐oven experiments. Its dissociation energy D°298 = 50.1 ± 0.3 kcal mole−1 was determined using the third‐law method. The equilibrium reaction As4⇋2As2 was considered in the study of the vapor over GaAs. Second‐law and third‐law values D°298 = 77 ± 5 and 73.5 ± 0.3 kcal mole−1, respectively, for the As2–As2 bond were obtained. The value D°298 = 71.0 ± 3.0 kcal mole−1 is proposed as a result of comparison with previous determinations.

MASS-SPECTROMETRIC STUDY OF THE YTTRIUM-CARBON SYSTEM

A high‐temperature investigation of the vapor in thermodynamic equilibrium with Y–C condensed system was carried out in the temperature range 2075°—2340°K. Y and YC2 are shown to be important species in the vapor phase. Utilizing the pressure‐independent reaction Y(g)+2C(s)→YC2(g), second‐ and third‐law methods yielded D00=155±6 kcal mole−1 and D00=156±5 kcal mole−1, respectively, for the Y–C2 bond energy. An estimated heat of formation ΔH°f298=−27±6 kcal mole−1 for solid dicarbide is also obtained.Comparison between Me—C2 and Me—O bond strengths is made for Group IIIA elements and for the first two elements of the lanthanide series.

Simultaneous determination by knudsen-effusion microcalorimetric technique of the vapor pressure and enthalpy of vaporization of pyrene and 1,3,5-triphenylbenzene☆

Abstract Simultaneous determinations of the vapor pressure and of the enthalpy of sublimation of pyrene and 1,3,5-triphenylbenzene were carried out by use of a Calvet microcalorimeter. The vapor pressure equations are: log 10 ( p / atm )=8.848–5091 ( K / T ) for solid pyrene (348 to 419 K ); log 10 ( p / atm )=12.208–7419 ( K / T ) for solid 1,3,5-triphenylbenzene (410 to 444 K ); log 10 ( p / atm )=9.275–6089 ( K / T ) for liquid 1,3,5-triphenylbenzene (454 to 500 K ); The values ΔH sub o (298.15 K) = (24.15 ± 0.13) and (36.33 ± 0.07) kcal th mol −1 were obtained for pyrene and 1,3,5-triphenylbenzene, respectively. The enthalpy of fusion of 1,3,5-triphenylbenzene, (5480 ± 70) cal th mol −1 , was measured and the thermodynamic functions for the pyrene gaseous molecule were also calculated.

Simultaneous determination by Knudsen effusion microcalorimetry of the vapour pressure and the enthalpy of sublimation of p- and m-nitroaniline

A Calvet microcalorimeter was used for the simultaneous determination of the enthalpy of sublimation and of the vapour pressure under Knudsen conditions of p - and m -nitroaniline. The vapour pressure equations are, for p -nitroaniline: log ⁡ 10 ( p / atm ) = ( 9 . 0 6 ± 0 . 0 8 ) - ( 5 1 1 8 ± 3 3 ) T / K , ( 3 5 1 t o 4 1 7 K ) , and for m -nitroaniline: log ⁡ 10 ( p / atm ) = ( 9 . 5 0 ± 0 . 0 9 ) - ( 4 8 9 0 ± 3 0 ) T / K , ( 3 2 0 t o 3 8 4 K ) . The values Δ H s u b ° ( 298.15 K ) = ( 2 4 . 1 ± 0 . 3 ) k c a l t h m o l - 1 , and Δ H s u b ° ( 298.15 K ) = ( 2 3 . 1 ± 0 . 3 ) k c a l t h m o l - 1 , are proposed for the enthalpy of sublimation of p - and m -nitroaniline respectively.

Dissociation energy of CeO2 and Ce2O2 molecules

A combination of Knudsen effusion and mass spectrometric techniques has been employed in studying the gaseous species in thermodynamic equilibrium with condensed CeO2 and with condensed Ce–CeO2 mixtures. A thermodynamic treatment of ion currents yields a value of ΔH°298=135±6 kcal mole−1 for the heat of vaporization of CeO2(s). The following reactions: Ce(g)+CeO2(g)⇄ 2CeO(g), (1), Ce2O2(g)⇄ 2CeO(g), (2), have been studied and it has been found that ΔH°298=−19±4 kcal mole−1 and ΔH°298=90±6 kcal mole−1 for Reactions (1) and (2), respectively. Utilizing these heats of reaction, the CeO2 and Ce2O2 atomization energies at 298°K were determined to be D°298(CeO2)=350±15 kcal mole−1 and D°298(Ce2O2)=474±15 kcal mole−1.

Dissociation Energy of the Gaseous AlP Molecule

The Knudsen cell‐mass spectrometric technique has been used to identify the heteronuclear molecule TlBi. The thermodynamic treatment of the data led to a value of the dissociation energy D0° (TlBi)=28 ± 3 kcal mole−1. A comparison between bond energies in condensed and gaseous IIIb—Vb binary compounds is reported.

Simultaneous microcalorimetric-Knudsen effusion determination of the sublimation enthalpy and vapor pressure of 1,2- and 1,4-dihydroxy anthraquinones

The enthalpies of sublimation δ H sub o ( T ) and the vapor pressures p of 1,2- and 1,4-dihydroxy anthraquinones were simultaneously measured by a microcalorimetric-Knudsen effusion technique. A Calvet microcalorimeter was utilized. 1,2-dihydroxy anthraquinone (434 to 504 K): Δ H s u b ° ( T ) / ca l t h m o l - 1 = ( 32449 ± 46 ) − ( 7.26 ± 0.10 ) T / K ; log ⁡ 10 ( p / atm ) = ( 9 . 4 2 ± 0 . 0 5 ) - ( 6 3 6 8 ± 2 6 ) K / T . 1,4-dihydroxy anthraquinone (394 to 463 K): Δ H s u b ° ( T ) / c a l t h m o l - 1 = ( 33003 ± 43 ) − ( 9.46 ± 0.1 ) T / K ; log ⁡ 10 ( p / atm ) = ( 1 0 . 8 7 ± 0 . 0 9 ) - ( 6 3 7 0 ± 39 ) K / T .

Vapor pressure of rubidium and dissociation energy of Rb2

The vapor pressure of liquid rubidium in the temperature range 402 to 551 K has been determined by thermogravimetric and mass-spectrometric techniques. The value (19.0 ± 0.5) kcal th mol −1 is proposed for the evaporation enthalpy of the element at 298.15 K. The dissociation energy: D °( T = 0) = (10.0 ± 0.5) kcal th mol −1 of the Rb 2 molecule has been also determined.