Direct determination of enthalpies of vaporization of liquid compounds by a miniaturized effusion cell adapted to a commercial microcalorimeter

Abstract

A miniaturized effusion cell adapted to a Sorpt~on LKB microcatorimeter has been designed, built and tested. Vaporization is performed isothermally into a vacuum through a small orifice permitting a vapour pressure very close to the equilibrium values. The cell has been tested by measuring the enthalpies of vaporization at 298.15 K of reference liquid compounds (water, benzene, propanol-1, propanol-2) with a reproducibility better than 1%. Enthalpies of vaporization of butanol-1 and deuterated water have also been determined.Accurate knowledge of the enthalpies of vaporization of both liquid and solid compounds is of greatest importance in a wide spectrum of thermodynamic calculations, from enthalpies of formation [1] to enthalpies of solvation [2]. This accuracy is the more indispensable the weaker the interactions concerned are. In particular, AvapH values are employed to obtain enthalpies of solvation from solution heats at infinite dilution, allowing a closer description of the solute-solvent interactions [3, 4], as well as the possible partition of different contributions (e.g. solvent restructuring effect and hydrophobic interactions).The additive character of the vaporization enthalpies has been proved but the correlations so far established [5][6][7][8] are restricted to liquid compounds of relatively small dimensions and simple molecular structure (e.g. with linear chain substituents). Direct and very precise determinations of vaporization enthalpies are thus increasingly required, particularly in connection with the more widespread employment of highsensitivity microcalorimeters.Several experimental techniques for the calorimetric determination of vaporization enthalpies for both liquid and solid compounds have been developed in the last twenty years |9-16], Part are based on the measurement of the heat required to vaporize a well-known amount of substance into a vacuum under defined conditions as close as possible to the equilibrium values. These direct methods have proved useful, but their 9

On the Transferability of Three Water Models Developed by Adaptive Force Matching

“…The computer resources for this study were provided by the Arkansas High Performance Computational Center through grant MRI-R2 #0959124 provided by the NSF. * at 298K ; + at 303 K 1, ref [7]; 2, ref [38]; 3, ref [46]; 4, ref [7]; 5, ref [42]; 6, ref [38]; 7, ref [17]; 8, ref [18]; 9, ref [19]; 10, ref [63]; 11, ref [64], 12, ref [65,66]; 13, ref [67] 14, ref [68], 15, ref [45] Figure the curves were fits to the Antoine's equation that start at the T B and terminate at T C .…”

Thermodynamic Study of N-Methylformamide and N,N-Dimethyl-Formamide

“…The authors utilized a modified commercial sorption LKB microcalorimeter operating at 298.15 K. A miniaturized custom-made effusion cell was adapted to the microcalorimeter, and vaporization was performed isothermally into a vacuum through a small orifice, allowing a vapor pressure very close to the equilibrium value. The modified calorimeter was tested by measuring the enthalpies of vaporization at 298.15 K of several reference liquid compounds [ 49 ] (see Section S2 in the Supplementary Materials for more details). Barone et al’s work [ 16 ] appears to have been carried out meticulously, using a purified and dried sample and a claimed reproducibility of 1 percent.…”

“…Relative deviation from recommended data [ 50 , 51 , 52 ] was well below 1 percent (with the exception of rather volatile benzene, see Table S1 in the Supplementary Materials ). It is noteworthy, however, that the samples used for calorimeter testing [ 49 ] are more volatile than DMF and especially NMF. SimCor method ( Section 2.6 ) will be used to test the consistency of calorimetric with vapor pressures and heat capacities.…”

<em></em>Thermodynamic Study of <em>N</em>-methylformamide and <em>N,N</em>-Dimethyl-Formamide

“…Relative deviation from recommended data [50][51][52] was well below 1 percent (with the exception of rather volatile benzene, see Table S1 in the Supplementary Materials). It is noteworthy, however, that the samples used for calorimeter testing [49] are more volatile than DMF and especially NMF. SimCor method (Section 2.6) will be used to test the consistency of calorimetric ∆ g l H m with vapor pressures and heat capacities.…”