Marc Laffitte

Mesures calorimétriques des enthalpies de vaporisation et de sublimation par effusion; mise au point de la technique

Abstract The association of an effusion cell to a Tian-Calvet microcalorimeter offers the possibility of measuring, at 298.15 K, energies of vaporisation (or sublimation) of compounds, the vapour pressures of which range from 10−4 to 100 torr, with a reproducibility of 1%. The following results are obtained for enthalpies of vaporisation [(ΔHvap)m] of water (vapour pressure, 23.7 torr at 298.15 K), 43.84±0.29 kJ.mol−1; cyclohexane (vapour pressure, 97.5 torr at 298.15 K), 32.89±0.29 kJ.mol−1; hexamethylphosphotriamide (vapour pressure, 51.10−3 torr at 298.15 K), 61.1± 1.7 kJ.mol−1. In the present work, a critical study of the technique is also made.

Étude thermochimique des méthylnaphtalènes

Abstract Calorimetric measurements of enthalpies of change of state (sublimation or vaporization) of methylnaphthalenes gave the following results: 1-methylnaphthalene: (ΔH vap)m=(57.32±0.42) kJ mol−1 2-methylnaphthalene: (ΔH sub)m=(65.69±0.84) kJ mol−1 Combination of these values with those obtained by Speros and Rossini1 for enthalpies of combustion of these compounds makes it possible to determine their energy of isomerization more accurately. This energy is (2.97±2.41) kJ mol−1 and should be attributed to steric hindrance in the 1-methylnaphthalene molecule. The comparison of energies of conjugation, theoretical as well as experimental, which we have determine for both molecules studied, confirms the present result.

Enthalpies de mélange des alliages liquides de gallium et de germanium

Abstract The enthalpies of mixing of the liquid binary alloys of gallium and germanium were measured using a microcalorimeter. Despite what we could think from the phase diagram alone, the mixing is exothermic: X being the mole fraction of gallium. During this study, the melting enthalpy of germanium was measured. The authors found (37,260±1,200) J. mole −1 , in good agreement with the value given by Sommelet 1 (36,900 J. mole −1 ).

Enthalpie de formation, diagramme de phases et structure du système ternaire tellure-bismuth-antimoine à 737 K

By direct reaction calorimetry at 737 K, the enthalpy of formation for bismuth-antimony-tellurium ternary system has been measured over the mole fraction range for tellurium of 0.55 <XTe <1. From these measurements the nature and limits of co-existence of the phases has been deduced. In particular, the retrograde nature of the solidus surface of Bi2Te3Sb2Te3 solid solutions has been demonstrated.

Infinitely dilute solutions of gallium, indium, and thallium in mercury

The partial molar enthalpy of solution at infinite dilution in mercury has been measured for gallium and indium at 34°C and for thallium at 13 temperatures in the range −16 to 260°C. The corresponding partial molar enthalpies of mixing at infinite dilution of the liquid metals in mercury have been derived. The results are discussed of these and previous measurements on dilute solutions of Ga, In, and Tl in Hg.

Détermination Des Enthalpies De Référence De Formation à L'état Solide De Quelques Dérivés Pyranno-Pyranne Diones

Summary The heats of combustion and formation at 298.15 K of five methyl and dimethyl substituted pyrano-pyran - dione derivatives, in their solid state, were determined. Table I shows the results obtained. The combustion of 3-6-mg samples were carried out in a microbomb fitted in a Tian-Calvet microcalorimeter.

Thermodynamique des solutions électrolytiques

The pof oui iometrie study of Ilio neutralisation of monochloracetio acid in aqueous solutions (0,05 < c < 5 M) by sodium hydroxyde, in Na+(ClOi~) = 5M, at 298,15 K, reveals the existence of association-dissociation equilibria by hydrogen bond. Monomoric, dimeric and trimeric species which are in each case represented by the molecule and the monobasic ion, coexist in the solutions. A reactionscheme for their formation is proposed. The constants of formation of the different species are calculated.

Utilisation de modules á effet peltier pour l'obtention de la courbe dT/dt=f(t) en calorimétrie isopéribolique

Abstract A pile made of Peltier effect moduli has been used to isoperibol calorimetry to plot the dT/dt = f(t) curve or to determine the energy liberated during an experiment. The authors show that; 1. (1) the response of such a probe is linear; 2. (2) the reproducibility of measurements ranges between 0.1 and 3%. It varies in terms of the block introduced between the two moduli of the pile; 3. (3) the time constant of the pile used in these experiments is 70 sec.