共查询到20条相似文献,搜索用时 28 毫秒
1.
Ben Cherifa A. Rogez J. Jemal M. Mathieu J. C. 《Journal of Thermal Analysis and Calorimetry》2001,63(3):689-697
Using an isoperibol calorimeter for rapid reactions and a Calsol type microcalorimeter for slow processes, are applied to
determine the enthalpies of solution of two synthetic phosphate products in nitric acid. Namely, β tricalcium phosphate Ca3(PO4)2 and the calcium hydroxyapatite Ca10 (PO4)6 (OH)2 are measured by varying pH value of the solvent. Some dissolution mechanisms are proposed for various pH values. They are
ensured by complementary reactions of solution of Ca(NO3)2, Ca(H2 PO4)2 and H3 PO4 in the same solvents. An extrapolation of solution enthalpies to pH=7 leads to the enthalpy of solution of these products
in the pure water. These values are Δsol
H °=–138.3 kJ mol–1 for Ca3 (PO4)2 and –393.6 kJ mol–1 for Ca10 (PO4)6 (OH)2 .
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
H.D.B. Jenkins 《Chemical physics letters》1975,35(3):417-419
The enthalpy of solvation of the gaseous chromate ion, ΔHsolv0(CrO42?) (g) is estimated on the basis of recent lattice energy studies made in this laboratory, and a charge distribution assigned to the ion. On the basis of the assigned charge of ?0.57 proton units to the oxygen atoms of the CrO42? unit, the total lattice potential energies are found to be: Upot(Na2CrO4) = 1836 kJ mol?1; Upot(K2CrO4) = 1717 kJ mol?1; Upot(Rb2CrO4) = 1645 kJ mol?1 and Upot(Cs2CrO4) = 1598 kJ mol?1. The corresponding value for ΔHsolv0(CrO42?) (g) = ?1077 kJ mol?1. 相似文献
3.
Ben Abdelkader S. Ben Cherifa A. Coulet M. V. Khattech I. Rogez J. Jemal M. 《Journal of Thermal Analysis and Calorimetry》2004,77(3):863-871
Pure and well crystallised whitlockite Ca18Mg2H2(PO4)14 has been synthesized by precipitation from the magnesium and calcium nitrates and the diammonic phosphate. The product of
the reaction has been characterized by X-ray diffraction, IR spectroscopy and chemical analysis. Using differential conduction
calorimeters the enthalpies of solution of the whitlockite and of a mixture of the solid reactants - the tricalcium, the trimagnesium
and the dicalcium phosphates - have been measured at 25°C for various concentrations of solid in a 46 wt% nitric acid solution.
A combination of the enthalpies of solution with the enthalpies of formation of the reactants allows us to determine the standard
enthalpy of formation of the whitlockite. The value deduced, -27,93·103kJ mol-1, is compared to the standard enthalpies of formation of the trimagnesium and the tricalcium phosphates.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
Michèle Decouzon Jean-Fraçois Gal Jérôme Gayraud Pierre-Charles Maria Gian-Angelo Vaglio Paolo Volpe 《Journal of the American Society for Mass Spectrometry》1993,4(1):54-57
An accurate gas-phase acidity for germane (enthalpy scale, equivalent to the proton affinity of GeH3 ?), ΔH acid o(GeH4) = 1502.0 ± 5.1 kJ mol?1, is obtained by constructing a consistent acidity ladder between GeH4, and H2S by using Fourier transform-ion cyclotron resonance spectrometry, and 0 and 298.15 K values for the first bond dissociation energy of GeH4 are proposed: D0 o(H3Ge-H) = 352 ± 9 kJ mol?1; D o(H3Ge-H) = 358 ± 9 kJ mol?1, respectively. These results are compared with experimental and theoretical data reported in the literature. Methylgermane was found to be a weaker acid than germane by approximately 35 kJ mol?1: ΔH acid o = 1536.6 kJ mol?1. 相似文献
5.
The aqueous chemistry of phosphorus is dominated by P(V), which under typical environmental conditions (and depending on pH and concentration) can be present as the orthophosphate species H3PO 4 0 (aq),H2PO 4 ? (aq),HPO 4 2? (aq) or PO 4 3? (aq). Many divalent, trivalent and tetravalent metal ions form sparingly soluble orthophosphate phases that, depending on the solution pH and concentrations of phosphate and metal ions, can be solubility limiting phases. Geochemical and chemical engineering modeling of solubilities and speciation require comprehensive thermodynamic databases that include the standard thermodynamic properties for the aqueous species and solid compounds. The most widely used sources for standard thermodynamic properties are the NBS (now NIST) Tables (from 1982 and earlier, with a 1989 erratum) and the final CODATA evaluation (1989). However, a comparison of the reported enthalpies of formation and Gibbs energies of formation for key phosphate compounds and aqueous species, especially H2PO 4 ? (aq) and HPO 4 2? (aq), shows a systematic and nearly constant difference of 6.3 to 6.9 kJ?mol?1 per phosphorus atom between these two evaluations. The existing literature contains numerous studies (including major data summaries) that are based on one or the other of these evaluations. In this report we examine and identify the origin of this difference and conclude that the CODATA evaluation is more reliable. Values of the standard entropies of the H2PO 4 ? (aq) and HPO 4 2? (aq) ions at 298.15 K and p?° =1 bar were re-examined in the light of more recent information and data not considered in the CODATA review, and a slightly different value of S m o (H2PO 4 ? , aq, 298.15 K) = (90.6±1.5) J?K?1?mol?1 was obtained. 相似文献
6.
Introduction Since Anghileri firstly reported that complex of LaCl3 with glycine had the antitumor function in 1975,1 coordination compounds of rare earth with amino acid have attracted increasing attention.2-4 People have found that some compounds of rare earth with amino acids possess disinfection, elimination of inflammation, de-crease of the level of blood sugar and anti-cruor func-tions. Imidazole is a wreath compound, and presents unique biological activities. Ternary coordination com-… 相似文献
7.
《Journal of Inorganic and Nuclear Chemistry》1981,43(9):2059-2064
We have measured the enthalpy of reaction of AmO2, using 241Am and 243Am, in 0.5 M H2SO4−0.1 M KI solution. From this datum and auxiliary thermochemical measurements we have calculated ΔHf°(AmO2, C, 298.15 K) = −932.2 ± 2.7 kJ mol−1. We estimate ΔHf°(Am4+, aq, 298.15 K) = −406±6 kJ mol−1 and E°(Am4+/Am3+) = 262 ± 0.09 V. 相似文献
8.
《Journal of Inorganic and Nuclear Chemistry》1978,40(5):907-914
Zirconium phosphate was found to exchange alkaline earth cations in macro quantities from acetate solutions. Rates of exchange decrease with increasing crystallinity of the exchanger but increase appreciably with temperature. Magnesium ion exchange is very slow even at 100°C. Both Mg2+ and Ba2+ each form a single exchanged phase. Their respective compositions are close to ZrMg0.75−1.0H0.5−0(PO4)2·4H2O and ZrBa0.8−1.0H0.4−0 (PO4)2·2H2O. In contrast Ca2+ and Sr2+ each form phases with cation contents close to half-exchange, i.e. ZrCa0.5−0.65H1−0.7(PO4)2·3H2O and ZrSr0.45−0.55H1.1−0.9(PO4)2·3.5H2O. these phases are then converted to ZrCa0.85−1H0.3−0(PO4)2·4H2O and ZrSr0.65−1H0.7−0(PO4)2·2.5H2O, respectively at higher loadings. Apparently acetate ion is a sufficiently strong base to initiate exchange and then maintain pH values high enough to achieve high metal loadings. 相似文献
9.
IntroductionZincisanessentialtraceelementtothelife .Manydiseasesarousedfromadeficiencyofzincelementhavere ceivedconsiderableattention .L α Aminoacidsarebasicunitsofproteins .L α Trytophanisoneoftheeightspeciesofaminoacidsindispensableforlife ,whichhastobeab sorbedfromfoodbecauseitcannotbesynthesizedinthehumanbody .InviewofthecomplexesofL α trytophanandessentialelementsasaddictiveswidelyusedinsuchfieldsasfoodstuff,medicineandcosmetic ,1 3theyhaveabroadenprospectforapplications .Briefly ,ab… 相似文献
10.
Summary The third-law method has been applied to determine the enthalpies, ΔrHT0, for dehydration reactions of kaolinite, muscovite and talc. The ΔrHT0values measured in the equimolar (in high vacuum) and isobaric (in the presence of water vapour) modes (980±15, 3710±39 and
2793±34 kJ mol-1, for kaolinite, muscovite and talc, respectively) practically coincide if to take into account the strong self-cooling effect
in vacuum. This fact strongly supports the mechanism of dissociative evaporation of these compounds in accordance with the
reactions (primary stages): Al2O3·2SiO2·2H2O(s)→Al2O3(g)↓+2SiO2(g)↓+2H2O(g); K2O·3Al2O3·6SiO2·2H2O(s) →K2O(g)↓+3Al2O3(g)↓+6SiO2(g)↓+2H2O(g) and 3MgO·4SiO2·H2O(s) →3MgO(g)↓+4SiO2(g)↓+H2O(g). The values of the Eparameter deduced from these data for equimolar and isobaric modes of dehydration are as follows: 196 and 327 kJ mol-1for kaolinite, 309 and 371 kJ mol-1for muscovite and 349 and 399 kJ mol-1for talc. These values are in agreement with quite a few early results reported in the literature in 1960s. 相似文献
11.
J. Straszko M. Olszak-Humienik J. Możejko 《Journal of Thermal Analysis and Calorimetry》1997,48(6):1415-1422
The thermal decomposition of iron sulphate hexahydrate was studied by thermogravimetry at a heating rate of 5°C min?1 in static air. The kinetic parameters were evaluated using the integral method by applying the Coats and Redfern approximation. The thermal stabilities of the hydrates were found to vary in the order. Fe2(SO4)3·6H2O → Fe2(SO4)3·4.5H2O → Fe2(SO4)3·0.5H2O The dehydration process of hydrated iron sulphate was found to conform to random nucleation mass loss kinetics, and the activation energies of the respective hydrates were 89.82, 105.04 and 172.62 kJ mol?1, respectively. The decomposition process of anhydrous iron sulphate occurs in the temperature region between 810 and 960 K with activation energies 526.52 kJ mol?1 for the D3 model or 256.05 kJ mol?1 for the R3 model. 相似文献
12.
Tran TT Wang T Hack S Bowie JH 《Rapid communications in mass spectrometry : RCM》2011,25(17):2489-2499
The low‐energy negative ion phosphoTyr to C‐terminal ‐CO2PO3H2 rearrangement occurs for energised peptide [M–H]– anions even when there are seven amino acid residues between the pTyr and C‐terminal amino acid residues. The rearranged C‐terminal ‐CO2PO2H(O–) group effects characteristic SNi cyclisation/cleavage reactions. The most pronounced of these involves the electrophilic central backbone carbon of the penultimate amino acid residue. This reaction is aided by the intermediacy of an H‐bonded intermediate in which the nucleophilic and electrophilic reaction centres are held in proximity in order for the SNi cyclisation/cleavage to proceed. The ΔGreaction is +184 kJ mol?1 with the barrier to the SNi transition state being +240 kJ mol?1 at the HF/6‐31 + G(d)//AM1 level of theory. A similar phosphate rearrangement from pTyr to side chain CO2– (of Asp or Glu) may also occur for energised peptide [M–H]– anions. The reaction is favourable: ΔGreaction is ?44 kJ mol?1 with a maximum barrier of +21 kJ mol?1 (to the initial transition state) when Asp and Tyr are adjacent. The rearranged species R1‐Tyr‐NHCH(CH2CO2PO3H–)COR2 (R1 = CHO; R2 = OCH3) may undergo an SNi six‐centred cyclisation/cleavage reaction to form the product anion R1‐Tyr(NH–). This process has a high energy requirement [ΔGreaction = +224 kJ mol?1, with the barrier to the SNi transition state being +299 kJ mol?1]. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
13.
Mixtures of CaHPO4, CaCO3, and Na2CO3 were heated at 870°C under steam or under dry CO2 until phase composition and weight were constant. According to chemical analysis and X-ray diffractometry the stability field of the β-Ca3(PO4)2 phase is limited by the molar P/Ca ratio of 0.664 ± 0.003 and 0.675 ± 0.010 irrespective of the partial water vapour pressure. A continuous series of solid solutions was found between β-Ca3(PO4)2 and a new whitlockite with the composition Ca10Na(PO4)7. The IR spectrum of these solid solutions shows that the point symmetry of the PO4 groups and their environment increases with increasing sodium content. This is in agreement with data published about the structure of β-Ca3(PO4)2 and whitlockite. The composition of these solid solutions suggests that Na+ ions can replace H+ ions in the whitlockite structure. Carbonate and pyrophosphate ions are not incorporated in these whitlockites. 相似文献
14.
A small amount (≤ 10−6 mol fraction) of four alkaline earth metals, tin and yttrium were introduced into five, premixed, fuel-rich, H2–O2–N2 flames at atmospheric pressure in the temperature range 1820–2400 K. Aqueous salt solutions of the metals were sprayed into the premixed flame gas as an aerosol using an atomizer technique. Ions in a flame were observed by sampling flame gas through a nozzle into a mass spectrometer. The concentrations of the major neutral metallic species present in the flame were calculated from thermodynamic data currently available. The principal metallic ions observed were AOH+ (A = Mg, Ca, Sr, Ba, Sn) and A(OH)2+ (A = Y), formed initially by proton transfer to AO and OAOH from H3O+, a natural flame ion. Except for Mg, the ions were also produced by chemi-ionization processes. By adjusting the concentration(s) of the salt solution in the atomizer, it was found that a pair of ions could be brought into equilibrium within the time scale of the flame; the pairs included H3O+ with a metal ion or two metallic ions. Because water is a major product of combustion, a very large difference in proton affinity PA0(AO) − PA0(H2O) ≤ 490 kJ mol−1 (117 kcal mol−1) could be attempted for the proton transfer equilibrium. Using PA0(H2O) = 691.0 kJ mol−1 (165.2 kcal mol−1) as a reference base to anchor the proton affinity scale, ion ratio measurements led to proton affinity PA0 values of 766, 912, 1004, 1184, 1201, and 1222 kJ mol−1 (183, 218, 240, 283, 287, and 292 kcal mol−1) corrected to 298 K for OYOH, SnO, MgO, CaO, SrO, and BaO, respectively; of these, only the value for OYOH has not been reported previously. If it is assumed that the neutral thermodynamic data are correct (although some appear to be in error), the uncertainties in the PA results reported here are ± 21 kJ mol−1 (5 kcal mol−1). The realization that these equilibria can be achieved in flames provides a new approach to consolidate and build the high end of the proton affinity ladder, primarily of metallic species which are not accessible at lower temperatures. 相似文献
15.
Mikhail N. Glukhovtsev Robert D. Bach Sergei Laiter 《International journal of quantum chemistry》1997,62(4):373-384
The heats of formation and strain energies for saturated and unsaturated three- and four-membered nitrogen and phosphorus rings have been calculated using G2 theory. G2 heats of formation (ΔHf298) of triaziridine [(NH)3], triazirine (N3H), tetrazetidine [(NH)4], and tetrazetine (N4H2) are 405.0, 453.7, 522.5, and 514.1 kJ mol−1, respectively. Tetrazetidine is unstable (121.5 kJ mol−1 at 298 K) with respect to its dissociation into two trans-diazene (N2H2) molecules. The dissociation of tetrazetine into molecular nitrogen and trans-diazene is highly exothermic (ΔH298 = −308.3 kJ mol−1 calculated using G2 theory). G2 heats of formation (ΔHf298) of cyclotriphosphane [(PH)3], cyclotriphosphene (P3H), cyclotetraphosphane [(PH)4], and cyclotetraphosphene (P4H2) are 80.7, 167.2, 102.7, and 170.7 kJ mol−1, respectively. Cyclotetraphosphane and cyclotetraphosphene are stabilized by 145.8 and 101.2 kJ mol−1 relative to their dissociations into two diphosphene molecules or into diphosphene (HP(DOUBLE BOND)PH) and diphosphorus (P2), respectively. The strain energies of triaziridine [(NH)3], triazirine (N3H), tetrazetidine [(NH)4], and tetrazetine (N4H2) were calculated to be 115.0, 198.3, 135.8, and 162.0 kJ mol−1, respectively (at 298 K). While the strain energies of the nitrogen three-membered rings in triaziridine and triazirine are smaller than the strain energies of cyclopropane (117.4 kJ mol−1) and cyclopropene (232.2 kJ mol−1), the strain energies of the nitrogen four-membered rings in tetrazetidine and tetrazetine are larger than those of cyclobutane (110.2 kJ mol−1) and cyclobutene (132.0 kJ mol−1). In contrast to higher strain in cyclopropane as compared with cyclobutane, triaziridine is less strained than tetrazetidine. The strain energies of cyclotriphosphane [(PH)3, 21.8 kJ mol−1], cyclotriphosphene (P3H, 34.6 kJ mol−1), cyclotetraphosphane [(PH)4, 24.1 kJ mol−1], and cyclotetraphosphene (P4H2, 18.5 kJ mol−1), calculated at the G2 level are considerably smaller than those of their carbon and nitrogen analog. Cyclotetraphosphene containing the P(DOUBLE BOND)P double bond is less strained than cyclotetraphosphane, in sharp contrast to the ratio between the strain energies for the analogous unsaturated and saturated carbon and nitrogen rings. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62 : 373–384, 1997 相似文献
16.
利用瞬态吸收光谱技术研究了不同条件下C6H5Cl与H2O2水溶液的激光闪光光解情况, 初步考察了其瞬态物种的生长和衰减等行为. 研究表明, •OH自由基和C6H5Cl反应生成C6H5Cl-OH adduct, 其反应速率常数在近中性、酸性条件下约为(5.89±0.65)×109和(7.07±0.61)×109 L•mol-1•s-1; 其衰减则符合双分子二级反应, 速率常数2k/εl=1.1×106 s-1, 而在碱性时则为(4.34±0.51)×109 L•mol-1•s-1, 衰减呈准一级反应, 速率常数为2.11×105 s-1. 在有氧条件下, O2与C6H5Cl-OH adduct反应生成C6H5Cl-OHO2 adduct, 其反应速率常数为6.8×108 L•mol-1•s-1. 相似文献
17.
The equilibrium between fluoral in dichloromethane solution and live condensed liquid polyfluoral has been investigated between 22 and 43°C. Equilibrium monomer concentrations gave: ΔHac°(298 K) = -50-8 ± 2·3 kJ mol?1 and ΔSsc° (298 K) = -142·7 ± 7·4 J K-1 mol-1. With the aid of calibration and monomer vaporization data, thermodynamic values for the polymerization of liquid monomer to liquid polymer were also calculated: ΔHtc° (298 K) = -47 ± 3 kJ mol-1 and ΔS1e° (298 K) = -97 ± 10 J K-1 mol-1. 相似文献
18.
L. Xu Y. De-Jun L. Qiang-Guo L. Ai-Tao Y. Li-Juan J. Qian-Hong L. Yi 《Journal of Thermal Analysis and Calorimetry》2009,95(2):579-584
The product from reaction of samarium chloride hexahydrate with salicylic acid and Thioproline, [Sm(C7H5O3)2·(C4H6NO2S)]·2H2O, was synthesized and characterized by IR, elemental analysis, molar conductance, and thermogravimetric analysis. The standard molar enthalpies of solution of [SmCl3·6H2O(s)], [2C7H6O3(s)], [C4H7NO2S(s)] and [Sm(C7H5O3)2·(C4H7NO2S)·H2O(s)] in a mixed solvent of absolute ethyl alcohol, dimethyl sulfoxide(DMSO) and 3 mol L?1 HCl were determined by calorimetry to be Δs H m Φ [SmCl3 δ6H2O (s), 298.15 K]= ?46.68±0.15 kJ mol?1 Δs H m Φ [2C7H6O3 (s), 298.15 K]= 25.19±0.02 kJ mol?1, Δs H m Φ [C4H7NO2S (s), 298.15 K]=16.20±0.17 kJ mol?1 and Δs H m Φ [Sm(C7H5O3)2·(C4H6NO2S)]·2H2O (s), 298.15 K]= ?81.24±0.67 kJ mol?1. The enthalpy change of the reaction (1) $$ SmCl_3 \cdot 6H_2 O(s) + 2C_7 H_6 O_3 (s) + C_4 H_7 NO_2 S(s) = Sm(C_7 H_5 O_3 )_2 \cdot (C_4 H_6 NO_2 S) \cdot 2H_2 O(s) + 3HCl(g) + 4H_2 O(1) $$ was determined to be Δs H m Φ =123.45±0.71 kJ mol?1. From date in the literature, through Hess’ law, the standard molar enthalpy of formation of Sm(C7H5O3)2(C4H6NO2S)δ2H2O(s) was estimated to be Δs H m Φ [Sm(C7H5O3)2·(C4H6NO2S)]·2H2O(s), 298.15 K]= ?2912.03±3.10 kJ mol?1. 相似文献
19.
《Journal of Coordination Chemistry》2012,65(6):481-491
The complexes [N2(L2)2(H2O)4]Cl4(1) and [Ni(L2)](ClO4)2 [sdot]2H2O (2) (L = 1,3,10,12,16,19-hexaazatetracyclo [17,3,1,1 12.16,04.9]tetracosane) have been synthesized and structurally characterized by X-ray crystallography, spectroscopic and cyclic voltammetry. The crystal structure of 1 has a distorted octahedral geometry with two secondary and two tertiary amines of the macrocycle and two water molecules. In 2, the coordination geometry around the nickel atom is square-planar with four nitrogen atoms of the macrocycle. The equilibrium [Ni(L2)]2+ + 2H2O &rlhar2; [Ni(L2)(H2O)2]2+ has been studied in aqueous solution over a temperature range, yielding Δ H° = -19.0 ± 0.2 kJ mol-1 and Δ S° = - 56.0 ± 0.4 JK-1 mol-1. Cyclic voltammetry of the complexes give two one-electron waves corresponding to Ni(II)/Ni(III) and Ni(II)/Ni(I) processes. The electronic spectra and redox potentials of the complexes are influenced significantly by the geometry. 相似文献
20.
Y. R. Zhao J. X. Dong Y. Liu S. S. Qu 《Journal of Thermal Analysis and Calorimetry》2007,90(2):565-568
The two complexes, [RE(Gly)4(Im)(H2O)](ClO4)3(s)(RE = Eu, Sm), have been synthesized and characterized. The standard molar enthalpies of reaction for the following reactions,
RECl3·6H2O(s)+4Gly(s)+Im(s)+3NaClO4(s) = =[RE(Gly)4(Im)(H2O)](ClO4)3(s)+3NaCl(s)+5H2O(l), were determined by solution-reaction colorimetry. The standard molar enthalpies of formation of the two complexes at
T = 298.15 K were derived as Δf
H
mΘ {Eu(Gly)4(Im)(H2O)}(ClO4)3(s)} = = −(3396.6±2.3) kJ mol−1 and Δf
H
mΘ {Sm(Gly)4(Im)(H2O)}(ClO4)3(s)} = −(3472.7±2.3) kJ mol−1, respectively. 相似文献