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Thermochemical Study (thermochemical + study)

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Chemistry100%

Selected Abstracts

Thermochemical Study on the Chiral Sodium Zincophosphate Nanocrystalline

CHINESE JOURNAL OF CHEMISTRY, Issue 4 2006
Jian Wu
Abstract Chiral sodium zincophosphate nanocrystalline has been prepared and characterized. The standard molar enthalpy of the following reaction 12Na3PO4·12H2O(s)+12ZnSO4·7H2O(s)=Na12(Zn12P12O48)·12H2O(s)+12Na2SO4(s)+216H2O(l) was determined by solution reaction calorimetric at 298.15 K, and calculated to be 33.666±0.195 kJ/mol. From the results and other auxiliary quantities, the standard enthalpy of formation for sodium zincophosphate nanocrystalline was derived to be , fH,m [Na12(Zn12P12O48)·12H2O(s), 298.15 K]=,24268.494±0.815 kJ/mol. [source]

Thermochemical Properties and Decomposition Kinetics of Ammonium Magnesium Phosphate Monohydrate

CHINESE JOURNAL OF CHEMISTRY, Issue 1 2007
Jian Wu
Abstract Ammonium magnesium phosphate monohydrate NH4MgPO4·H2O was prepared via solid state reaction at room temperature and characterized by XRD, FT-IR and SEM. Thermochemical study was performed by an isoperibol solution calorimeter, non-isothermal measurement was used in a multivariate non-linear regression analysis to determine the kinetic reaction parameters. The results show that the molar enthalpy of reaction above is (28.795±0.182) kJ/mol (298.15 K), and the standard molar enthalpy of formation of the title complex is (,2185.43±13.80) kJ/mol (298.15 K). Kinetics analysis shows that the second decomposition of NH4MgPO4·H2O acts as a double-step reaction:an nth-order reaction (Fn) with n=4.28, E1=147.35 kJ/mol, A1=3.63×1013 s,1 is followed by a second-order reaction (F2) with E2=212.71 kJ/mol, A2=1.82×1018 s,1. [source]

Hetero-,-systems from 2 + 2 cycloreversion, part 2.1Ab initio thermochemical study of heterocyclobutanes 2 + 2 cycloreversion to form heteroethenes H2C=X (X=NH, O, SiH2, PH, S),

HETEROATOM CHEMISTRY, Issue 7 2007
Leonid E. Gusel'nikov
Ab initio and DFT thermochemical study of diradical mechanism of 2 + 2 cycloreversion of parent heterocyclobutanes and 1,3-diheterocyclobutanes, cyclo -(CH2CH2CH2X), and cyclo -(CH2XCH2X), where X = NH, O, SiH2, PH, S, was undertaken by calculating closed-shell singlet molecules at three levels of theory: MP4/6-311G(d)//MP2/6-31G(d)+ZPE, MP4/6-311G(d,p)//MP2/6-31G (d,p)+ZPE, and B3LYP/6-311+G(d,p)+ZPE. The enthalpies of 2 + 2 cycloreversion decrease on going from group 14 to group 16 elements, being substantially higher for the second row elements. Normally endothermic 2 + 2 cycloreversion is predicted to be exothermic for 1,3-diazetidine and 1,3-dioxtane. Strain energies of the four-membered rings were calculated via the appropriate homodesmic reactions. The enthalpies of ring opening via the every possible one-bond homolysis that results in the formation of the corresponding 1,4-diradical were found by subtracting the strain energies from the central bond dissociation energies of the heterobutanes CH3CH2,CH2XH, CH3CH2,XCH3, and HXCH2,XCH3. The latter energies were determined via the enthalpies of the appropriate dehydrocondensation reactions, using C,H and X,H bond energies in CH3XH calculated at G2 level of theory. Except 1,3-disiletane, in which ring-opening enthalpy attains 69.7 kcal/mol, the enthalpies of the most economical ring openings do not exceed 60.7 kcal/mol. The 1,4-diradical decomposition enthalpies found as differences between 2 + 2 cycloreversion and ring-opening enthalpies were negative, the least exothermicity was calculated for , CH2SiH2CH2CH2. The only exception was 1,3-disiletane, which being diradical, CH2SiH2CH2SiH2, decomposed endothermically. Since decomposition of the diradical containing two silicon atoms required extra energy, raising the enthalpy of the overall reaction to 78.9 kcal/mol, 1,3-disiletane was predicted to be highly resisting to 2 + 2 cycloreversion. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:704,720, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20377 [source]