Authors:Xian'e Cia, Daichun Du, Youming Jin, and Yixiang Qian
N(C5F11)3 (Fluorint FC-70) has been chosen as the test material to compare the chemicophysical data obtained by static-sample and DSC
The normal boiling point, the molar enthalpy of vaporization, and the constants of the Antoine equation of fluorint FC-70
DSC can be developed into a simple and rapid routine instrument to determine the enthalpy of vaporization as well as the boiling
point of liquid, particularly at relative high temperature.
A miniaturized effusion cell adapted to a Sorption LKB microcalorimeter 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.
Authors:V. Ovchinnikov, E. Sagadeev, L. Lapteva, L. Khasieva, M. Alikberov, E. Sitnikova, I. Antipin, I. Stoikov, and A. Konovalov
The enthalpies of vaporization of different classes of phosphorylated alcohols and amines were determined from their enthalpies
of solution in hexane and carbon tetrachloride. The enthalpies of specific (hydrogen-bond) interaction with the solvents (chloroform
and pyridine) of derivatives containing X-H groups (X=O or N) in the α-position to the P=O group were determined. The results
were explained in terms of the spatial structure of such compounds.
Authors:V. Ovchinnikov, T. Makeeva, L. Lapteva, V. Valiullina, L. Pilishkina, and A. Konovalov
The enthalpies of vaporization of different classes three-coordinated arsenic compounds have been determined according to
their enthalpies of solution in hexane and molar refraction. The enthalpies of solvation of cyclic and acyclic As(III)-derivatives
in hexane, carbon tetrachloride,p-xylene and pyridine are obtained and discussed.
Ibuprofen has been subjected to a TG/DTA study over the temperature range of 30 to 350°C in a flowing atmosphere of nitrogen.
The heating rate and the flow rate were varied. The DTA shows a melting at around 80°C and boiling point range from 212 to
251°C depending upon the heating rate. The mass loss in the TG data confirms the evaporation of Ibuprofen between them.p. and the normalb.p. Evaporation is limited to the surface area, which is a constant in the crucible holding the sample. The DTG plot shows clearly
a zero order process which is consistent with the process of evaporation. The enthalpy of vaporization (ΔvapH) calculated by Trouton's rule is found to be in the range of 42.7–46.1 kJ mol−1. TheEact for the zero order reaction is in the range of 81.8–87.0 kJ mol−1 and is calculated by use of the derivative method. The value ofEact is about twice that for ΔHvap in Ibuprofen and differs from other compounds, whereEact≈Δ Hvap. It is suggested that the Ibuprofen molecule is existing as a dimer in the liquid state and dissociates to a monomer in the
The standard (p0=0.1
MPa) molar enthalpies of formation, in the condensed phase, of nine linear-alkyl
substituted thiophenes, six in position 2- and three in position 3-, at T=298.15 K, were derived from the standard massic
energies of combustion, in oxygen, to yield CO2(g)
measured by rotating-bomb combustion calorimetry. The standard molar enthalpies
of vaporization of these compounds were measured by high temperature Calvet
Microcalorimetry, so their standard molar enthalpies of formation, in the
gaseous phase, were derived.
The results are discussed in terms
of structural contributions to the energetics of the alkyl-substituted thiophenes,
and empirical correlations are suggested for the estimation of the standard
molar enthalpies of formation, at T=298.15
K, for 2- and 3-alkyl-substituted thiophenes, both in the condensed and in
the gaseous phases.
of the liquid 2-methylfuran, 5-methyl-2-acetylfuran and 5-methyl-2-furaldehyde were derived from the standard molar energies
of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was
used to measure the enthalpies of vaporization of the three compounds. The standard (po = 0.1 MPa) molar enthalpies of formation of the compounds, in the gaseous phase, at T = 298.15 K have been derived from the corresponding standard molar enthalpies of formation in the liquid phase and the standard
molar enthalpies of vaporization. The results obtained were −(76.4 ± 1.2), −(253.9 ± 1.9), and −(196.8 ± 1.8) kJ mol−1, for 2-methylfuran, 5-methyl-2-acetylfuran, and 5-methyl-2-furaldehyde, respectively.
Authors:Maria Ribeiro da Silva, Joana Cabral, Chelsea Givens, Stephanie Keown, and W. Acree
The standard (p0=0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T-298.15 K, for 2,5-dimethylpyrazine (2,5-DMePz) and for the two dimethylpyrazine-N,N′-dioxide derivatives, 2,3-dimethylpyrazine-1,4-dioxide (2,3-DMePzDO) and 2,5-dimethylpyrazine-1,4-dioxide (2,5-DMePzDO), were
derived from the measurements of standard massic energies of combustion, using a static bomb calorimeter, and from the standard
molar enthalpies of vaporization or sublimation, measured by Calvet microcalorimetry.
The mean values for the molar dissociation enthalpy of the nitrogen-oxygen bonds, 〈DHm0〉(N-O), were derived for both N,N′-dioxide compounds. These values are discussed in terms of the molecular structure of the two N,N′-dioxide derivatives and compared with 〈DHm0〉(N-O) values previously obtained for other N-oxide derivatives.
The standard (p0=0.1 MPa) molar enthalpy of formation, ΔfHm0(l)=169.8±2.6 kJ mol−1, of the liquid 3-bromoquinoline was derived from its standard molar energy of combustion, in oxygen, to yield CO2(g), N2(g) and HBr·600H2O(l), at T=298.15 K, measured by rotating bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was
used to measure the enthalpy of vaporization of the compound, Δ1gHm0=70.7±2.3 kJ mol−1. These two thermodynamic parameters yielded the standard molar enthalpy of formation, in the gaseous phase, at T=298.15 K, ΔfHm0(g)=240.5±3.5 kJ mol−1.