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

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 (ΔH_vap)_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.