Standard enthalpies of formation of amorphous platinum hydrous oxide PtH2.76O3.89 (Adams' catalyst) and dehydrated oxide PtO2.52 at T=298.15 K were determined to be -519.61.0 and -101.3 5.2 kJ mol-1, respectively, by micro-combustion calorimetry. Standard enthalpy of formation of anhydrous PtO2 was estimated to be -80 kJ mol-1 based on the calorimetry. A meaningful linear relationship was found between the pseudo-atomization enthalpies of platinum
oxides and the coordination number of oxygen surrounding platinum. This relationship indicates that the Pt-O bond dissociation
energy is 246 kJ mol-1 at T=298.15 K which is surprisingly independent of both the coordination number and the valence of platinum atom. This may provide
an energetic reason why platinum hydrous oxide is non-stoichiometric.
Authors:Sonia Jebri, Ali Bechrifa, and Mohamed Jemal
the standardenthalpyofformation of these products is impossible. However, this quantity can be calculated through a thermochemical cycle involving a succession of steps, for which the “sum” corresponds to the enthalpy of formation of the compounds
The energy of combustion of crystalline 3,4,5-trimethoxybenzoic acid in oxygen at T=298.15 K was determined to be -4795.91.3 kJ mol-1 using combustion calorimetry. The derived standard molar enthalpies of formation of 3,4,5-trimethoxybenzoic acid in crystalline
and gaseous states at T=298.15 K, ΔfHmΘ (cr) and ΔfHmΘ (g), were -852.91.9 and -721.72.0 kJ mol-1, respectively. The reliability of the results obtained was commented upon and compared with literature values.
Authors:V. Lukyanova, T. Papina, K. Didenko, and A. Alikhanyan
The standard enthalpy of combustion of crystalline silver pivalate, (CH3)3CC(O)OAg (AgPiv), was determined in an isoperibolic calorimeter with a self-sealing steel bomb, ΔcH0 (AgPiv, cr)= −2786.9±5.6 kJ mol−1. The value of standard enthalpy of formation was derived for crystalline state: ΔfH0(AgPiv,cr)= −466.9±5.6 kJ mol−1. Using the enthalpy of sublimation, measured earlier, the enthalpy of formation of gaseous dimer was obtained: ΔfH0(Ag2Piv2,g)= −787±14 kJ mol−1. The enthalpy of reaction (CH3)3CC(O)OAg(cr)=Ag(cr)+(CH3)3CC(O)O.(g) was estimated, ΔrH0=202 kJ mol−1.
Authors:W. Xinmin, Q. Chuansong, Q. Songsheng, and T. Zhicheng
Rare-earth perchlorate complex coordinated with glycine [Nd2(Gly)6(H2O)4](ClO4)6�5H2O was synthesized and its structure was characterized by using thermogravimetric analysis (TG), differential thermal analysis
(DTA), chemical analysis and elementary analysis. Its purity was 99.90%. Heat capacity measurement was carried out with a
high-precision fully-automatic adiabatic calorimeter over the temperature range from 78 to 369 K. A solid-solid phase transformation
peak was observed at 256.97 K, with the enthalpy and entropy of the phase transformation process are 4.438 kJ mol−1 and 17.270 J K−1 mol−1, respectively. There is a big dehydrated peak appears at 330 K, its decomposition temperature, decomposition enthalpy and
entropy are 320.606 K, 41.364 kJ mol−1 and 129.018 J K−1 mol−1, respectively. The polynomial equations of heat capacity of this compound in different temperature ranges have been fitted.
The standard enthalpy of formation was determined to be −8023.002 kJ mol−1 with isoperibol reaction calorimeter at 298.15 K.
Authors:Yu. Maksimuk, V. Sokolov, V. Sevruk, and P. Trahanov
The enthalpies of combustion for 4-formylbenzoic acid (I), 4-methylbenzyl alcohol (II), and trimethyl 1,2,4-benzenetricarboxylate
(III) were determined by the bomb calorimetry method. Enthalpies of sublimation for I and II were measured with a calorimeter.
The contributions of different substituents to the standard enthalpies of formation for benzene derivatives in the gas state
/kJ mol−1 = −259.0 ± 1.6 (LiSC2H5), −199.9 ± 1.8 (NaSC2H5), −254.9 ± 2.4 (NaSC4H9), −240.6 ± 1.9 (KSC2H5), −235.8 ± 2.0 (CsSC2H5). These results where compared with the literature values for the corresponding alkoxides and together with values for
From measurements of the enthalpy of solution of metal salts of 3-nitro-1,2,4-triazol-5-one (NTO) in water, the standard enthalpies
of formation of KNTO·H2O, Ba(NTO)2·3H2O, LiNTO·2H2O, Ca(NTO)2·4H2O and Gd(NTO)3·7H2O were determined as −(676.9±2.6), −(1627.0±2.5), −(966.6.3±2.2), −(1905.5±4.4) and −(3020.1±6.4) kJ·mol−1, respectively. From measurements of the enthalpy of precipitation of KNTO·H2O crystal with Pb(NO3)2(aq), CuSO4(aq) and Zn(NO3)2(aq), the standard enthalpies of formation of Pb(NTO)2·H2O, Cu(NTO)2·2H2O and Zn(NTO)2·H2O were determined as −(247.4±5.9), −(712.1±5.4) and −(628.8±5.7) kJ·mol−1, respectively.
Authors:K. Ardhaoui, J. Rogez, A. Ben Chérifa, M. Jemal, and P. Satre
Lanthanum-bearing silicate-oxyapatites or britholites, Ca10–xLax(PO4)6–x(SiO4)xO with 1≤x≤6, have been synthesized by solid state reaction
at high temperature. They were characterized by X-ray diffraction and IR spectroscopy.
Using two microcalorimeters, the heat of solution of these compounds have
been measured at 298 K in a solution of nitric and hydrofluoric acid. A strained
least squares method was applied to the experimental results to obtain the
solution enthalpies at infinite dilution, and the mixing enthalpy in two steps.
In the first step the mixing enthalpy obtained is referenced to the britholite
monosubstituted and to the oxysilicate. The mixing enthalpy referenced to
the oxyapatite and to the oxysilicate is then extrapolated. In order to determine
the enthalpies of formation of all the terms of the solution, thermochemical
cycles were proposed and complementary experiments were performed. The results
obtained show a decrease of the enthalpy of formation with the amount of Si
and La introduced in the lattice. This was explained by the difference in
the bond energies of (Ca–O, P–O) and (La–O, Si–O).