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1.
Spectroscopic and callorimetric measurements of temperature arid number density have been made using a 50-kW radio-frequency inductively coupled plasma (RFICP) torch operated at atmospheric pressure with maximum temperatures and electron densities near 8,1000 K and 2 x 1021 m3, respectively These measurements enabled the determination o/ the stale o/ equilibrium and of the corresponding applicability of rarious diagnostic techniques in hoth a recombining argon plasma and a recombining plasma with hydrogen or nitrogen. Results indicate that the Pure argon plasma is well described by u partial equilibrium model in which the free and bound-excited electrons are in mutual equilibrium irespective of possible departures from equilibrium with the ground state. The addition of just tenths of a percent of either atomic Hydrogen or nitrogen, however, disturbs this partial equilibrium hr argon plasmas with electron densities roughly less than 1021 m3 such that only diagnostic techniques which are independent o/ partial equilibrium assumptions can be reliably implemented. 相似文献
2.
A solution of cobalt(II) chloride in HCI is commonly used to examine various effects, such as changes in temperature and concentration, on the Co(H2O)62+/CoCl42– equilibrium (Lc Chaâtcliers principle). In aqucous solution the cobalt(II) ion exists as a mixture of two complex ions at equilibrium, blue CoCl42– and pink Co(H2O)62+. As the ions have different colors, it is easy to determine the position of the equilibrium. A series of experiments was designed to allow students to examine the concentration of chloride ion, the dehydration effect, and how dissociation effects the equilibrium. Different compounds were added to the aqueous solution of cobalt(II) ion, and the position of the equilibrium was determined either visually or, more quantitatively, by means of UV–vis spectroscopy. This exercise is suitable for general chemistry students and is designed to introduce them to the complexity of the actual chemical reaction rather than presenting them with a simplistic model. 相似文献
3.
Data characterizing the position of the equilibrium between Δ2- and Δ1-pyrazolines with alkyl substituents in different positions, which is established under the influence of potassium tertbutoxide in tert-butyl alcohol at 90°C, were obtained. 3-Alkyl-Δ2-pyrazolines are thermodynamically more stable than their isomers with different positions of the double bond, so that the fraction of the latter in equilibrium mixtures does not exceed 1–2%, and they are practically completely isomerized to the 3-Alkyl-Δ2-substituted derivatives. If the position of the side chains excludes the possibility of the formation of 3-alkyl-Δ2-pyrazolines by migration of the double bond (4-alkyl- and 5,5-dialkyl-substituted compounds), the fraction of Δ1-pyrazolines in the equilibrium rises appreciably and reaches 12% for 3,3-diethyl-Δ1-pyrazoline. 相似文献
4.
J. Devynck B. Trémillon M. Sloim H. Ménard 《Journal of Electroanalytical Chemistry》1977,78(2):355-369
In molten potassium hydrogenodifluoride (KHF2) fully ionized into K+ and HF2?, at 250°C, the HF2? ion is slightly dissociated according to the equilibrium: HF2?HF+F?. This is a solvent acid base equilibrium, HF being the strongest acid and F? the strongest base in this system. By means of a voltammetric study we showed that the hydrogen electrode may be used as an acidity indicator electrode in the whole acidity range of the melt. By analysis of the equilibrium potential variation in acidic and in basic media, the HF2? dissociation constant (melt autoprotolysis constant): KD = {HF} {F?} was determined The experimental value: KD=10?2.05 mol2 kg?2 is compared with a calculated one, issued from thermodynamic data. Results obtained with other electrodes (LaF3 monocrystal electrode and copper electrode) were discussed and compared with those obtained with the hydrogen electrode. 相似文献
5.
《Journal of Inorganic and Nuclear Chemistry》1978,40(6):975-978
The position of the equilibrium NO2−+O22−⇋NO2−+O2− is important for the nature of the basic species both in nitrite and nitrate melts. An analytical method for determining peroxide in a large excess of nitrite has been developed which enables values for the equilibrium constant in molten nitrite to be obtained that suggest the formation of peroxynitrite anions. Information is also presented on the reaction of these solutions with air, when peroxide acts as a catalyst for a slow oxidation of nitrite to nitrate, with glass when silicate is slowly formed, and with zirconium when no reaction was observed below 400°C. With platinum rapid reaction occurs, probably via a soluble peroxynitrite species, with the eventual precipitation of platinum(IV) oxide, a reaction of significance for some electrochemical measurements. 相似文献
6.
《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(1):130-137
We have shown previously that iodosylbenzene–iron(III ) porphyrin intermediates ( 2 ) are generated in the reactions of oxoiron(IV ) porphyrin π‐cation radicals ( 1 ) and iodobenzene (PhI), that 1 and 2 are at equilibrium in the presence of PhI, and that the epoxidation of olefins by 2 affords high yields of epoxide products. In the present work, we report detailed mechanistic studies on the nature of the equilibrium between 1 and 2 in the presence of iodoarenes (ArI), the determination of reactive species responsible for olefin epoxidation when two intermediates (i.e., 1 and 2 ) are present in a reaction solution, and the fast oxygen exchange between 1 and H218O in the presence of ArI. In the first part, we have provided strong evidence that 1 and 2 are indeed at equilibrium and that the equilibrium is controlled by factors such as the electronic nature of iron porphyrins, the electron richness of ArI, and the concentration of ArI. Secondly, we have demonstrated that 1 is the sole active oxidant in olefin epoxidation when 1 and 2 are present concurrently in a reaction solution. Finally, we have shown that the presence of ArI in a reaction solution containing 1 and H218O facilitates the oxygen exchange between the oxo group of 1 and H218O and that the oxygen exchange is markedly influenced by factors such as ArI incubation time, the amounts of ArI and H218O used, and the electronic nature of ArI. The latter results are rationalized by the formation of an undetectable amount of 2 from the reaction of 1 and ArI through equilibrium that leads to a fast oxygen exchange between 2 and H218O. 相似文献
7.
Xiangyang Cheng Zhonghua Zhang Qingyu Kong Qinghua Zhang Tao Wang Shanmu Dong Lin Gu Xiao Wang Jun Ma Pengxian Han Hong‐ji Lin Chien‐Te Chen Guanglei Cui 《Angewandte Chemie (International ed. in English)》2020,59(28):11477-11482
Sluggish kinetics and poor reversibility of cathode chemistry is the major challenge for magnesium batteries to achieve high volumetric capacity. Introduction of the cuprous ion (Cu+) as a charge carrier can decouple the magnesiation related energy storage from the cathode electrochemistry. Cu+ is generated from a fast equilibrium between copper selenide electrode and Mg electrolyte during standing time, rather than in the electrochemical process. A reversible chemical magnesiation/de‐magnesiation can be driven by this solid/liquid equilibrium. During a typical discharge process, Cu+ is reduced to Cu and drives the equilibrium to promote the magnesiation process. The reversible Cu to Cu+ redox promotes the recharge process. This novel Cu+ mediated cathode chemistry of Mg battery leads to a high reversible areal capacity of 12.5 mAh cm?2 with high mass loading (49.1 mg cm?2) of the electrode. 80 % capacity retention can be achieved for 200 cycles after a conditioning process. 相似文献
8.
《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(1):261-279
We report on the kinetics and ground‐state thermodynamics associated with electrochemically driven molecular mechanical switching of three bistable [2]rotaxanes in acetonitrile solution, polymer electrolyte gels, and molecular‐switch tunnel junctions (MSTJs). For all rotaxanes a π‐electron‐deficient cyclobis(paraquat‐p‐phenylene) (CBPQT4+) ring component encircles one of two recognition sites within a dumbbell component. Two rotaxanes (RATTF4+ and RTTF4+) contain tetrathiafulvalene (TTF) and 1,5‐dioxynaphthalene (DNP) recognition units, but different hydrophilic stoppers. For these rotaxanes, the CBPQT4+ ring encircles predominantly (>90 %) the TTF unit at equilibrium, and this equilibrium is relatively temperature independent. In the third rotaxane (RBPTTF4+), the TTF unit is replaced by a π‐extended analogue (a bispyrrolotetrathiafulvalene (BPTTF) unit), and the CBPQT4+ ring encircles almost equally both recognition sites at equilibrium. This equilibrium exhibits strong temperature dependence. These thermodynamic differences were rationalized by reference to binding constants obtained by isothermal titration calorimetry for the complexation of model guests by the CBPQT4+ host in acetonitrile. For all bistable rotaxanes, oxidation of the TTF (BPTTF) unit is accompanied by movement of the CBPQT4+ ring to the DNP site. Reduction back to TTF0 (BPTTF0) is followed by relaxation to the equilibrium distribution of translational isomers. The relaxation kinetics are strongly environmentally dependent, yet consistent with a single electromechanical‐switching mechanism in acetonitrile, polymer electrolyte gels, and MSTJs. The ground‐state equilibrium properties of all three bistable [2]rotaxanes were reflective of molecular structure in all environments. These results provide direct evidence for the control by molecular structure of the electronic properties exhibited by the MSTJs. 相似文献
9.
The (1:1) Na+ equilibrium constants, Ke1, of macrocyclic ethers of [12]crown-4, [12]crown-5 and [18]crown-6 were determined with a Na+ ISE in the presence of a second cation e.g. Li+, K+ and Ca2+ in dioxane/water (50/50). We estimated the (1:1) equilibrium constants, K e2 of the macrocyclic ethers with Li+, K+ and Ca2+ by this way. The binding selectivity of a macrocyclic ether between two cations was estimated in the same binary solvent
mixture where the water hydration role is diminished. Results showed clearly the effect of macrocyclic size and cation radii
in a solution.
Received October 27, 1998. Revision March 22, 1999. 相似文献
10.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1989,45(3):321-327
The temperature dependence of the Raman spectrum of 1,2-dithiacyclononane (1,2-DTCN) in the SS stretching region has been used to infer the existence of a conformational equilibrium with ΔH0 = 5.0 ± 0.8 kJ/mol. Molecular mechanics calculations predict a (2 2 5)-C2 lowest energy conformation in equilibrium with a (2 3 4) structure. The fully decoupled 13C NMR spectrum at −80°C and the Raman spectra are consistent with this postulate. The temperature dependence of the 1H NMR spectrum of 1,2-DTCN is characteristic of the ring inversion process. A crude lineshape analysis allows us to calculate ΔG0 = 49.0 ± 1.2 kJ/mol. 相似文献
11.
《Journal of Coordination Chemistry》2012,65(4):235-241
Abstract The reversible oxygenation of the Co(II) complex of tris(2-aminoethyl)amine (TREN, L) has been studied in some detail. The equilibrium constant K O2 =1026.92 M?2 atm?1, corresponding to the quotient [H+] [L2Co2(O2) (OH)3+]/[Co2+]2 [L]2 PO2 was determined by potentiometric equilibrium measurements of hydrogen ion concentration. Values for the thermodynamic constants, ΔH° =–63 ± 9 kcal/mole and ΔS° =–100 ± 15 cal/deg. mol, were calculated from the temperature dependence of the equilibrium constant. Oxygen stoichiometry, measured with a polarographic sensor, indicated the formation of a binuclear (peroxo bridged) complex, and the potentiometric equilibrium data indicated the presence of a second, μ-hydroxo, bridge. Measurement of the kinetics of the fast reaction between the cobalt(II)-TREN complex and dioxygen gave the value of the second order rate constant for the formation of the dioxygen complex as k 1 =2.8 × 10+3 sec?1 mol?1. The first order rate constant for the decomposition of the dioxygen complex measured by stopped-flow was found to be k ?2 =0.7 sec?1. Kinetic and equilibrium data are discussed with respect to the probable structure and mechanism of formation of the dioxygen complex, and are compared with similar data previously reported for analogous complexes. The oxygen complex reported is unique with respect to its extremely slow rate of conversion to inert cobalt(III) complexes. 相似文献
12.
The hydrate of 1,1,1,5,5,5-hexafluoro-2-hydroxy-2-methylpentan-4-one has been shown to exist in a hydrate-keto equilibrium in acetone and ether solutions using 1H and 19F magnetic resonance. The equilibrium percentages of the keto and hydrate forms as determined from 19F resonance are 30 and 70, respectively. 相似文献
13.
The halogen redistribution reaction in the binary [nBu2SnCl]2O/[nBu2SnBr]2O system is examined by 119Sn- and 13C-NMR spectroscopy. Binary mixtures of [nBu2SnCl]2O and [nBu2SnBr]2O reach equilibrium rapidly at room temperature. The reactant dimers are found to be in equilibrium with all five possible mixed distannoxane dimers in the equimolar mixture. These mixed distannoxane dimers differ in the ratio of Cl and Br as well as the relative positioning of the halogens. The mechanism responsible for the rapid formation of the mixed Cl:Br distannoxane dimers is found to proceed via bimolecular collisions producing a four-centered transition state, which in turn undergoes a concerted exchange of the halogens. The equilibrium concentrations of the reactant and product dimers are well represented by a statistical distribution, indicating that Cl and Br exhibit equivalent donor abilities. At 298 K, the NMR spectral data are consistent with time-averaged structures arising from rapidly interconverting rigid ladder pairs. Lowering the temperature to 173 K failed to freeze out this fluxional process. A reversible configurational rearrangement is also observed in which rotation about the oxygen---exocyclic tin bond results in the mutual exchange of halogens associated with the same exocyclic tin atom. 相似文献
14.
Ab initio MP2/aug’-cc-pVTZ calculations have been carried out to identify and characterize equilibrium structures and transition structures on the 1-oxo-3-hydroxy-2-propene: Lewis acid potential energy surfaces, with the acids LiH, LiF, BeH2, and BeF2. Two equilibrium structures, one with the acid interacting with the C=O group and the other with the interaction occurring at the O–H group, exist on all surfaces. These structures are separated by transition structures that present the barriers to the interconversion of the two equilibrium structures. The structures with the acid interacting at the C=O group have the greater binding energies. Since the barriers to convert the structures with interaction occurring at the O–H group are small, only the isomers with interaction occurring at the C=O group could be experimentally observed, even at low temperatures. Charge-transfer energies were computed for equilibrium structures, and EOM-CCSD spin–spin coupling constants 2hJ(O–O), 1hJ(H–O), and 1J(O–H) were computed for equilibrium and transition structures. These coupling constants exhibit a second-order dependence on the corresponding distances, with very high correlation coefficients. 相似文献
15.
Properties of Chalcogene-Chalcogene Bonds. XII. Reversible Telluration of Tetraisopropyldiphosphane, Stabilisation of Tellurobis(diisopropylphosphane) as Tetracarbonylchromium Complex Tetraisopropyldiphosphane 1 reacts with elemental tellurium by tellurium atom insertion to give tellurobis(diisopropylphosphane) 2. 2 is also available from sodium telluride with chlorodiisopropyl phosphane. lH, l3C, 3lP and l25Te n.m.r. spectra confirm that in solution 2 is in an equilibrium with the educt 1 and elemental tellurium. Reaction of this equilibrium mixture with tetracarbonyl(norbornadiene)chromium(0) provides tetracarbonyl[tellurobis(diisopropylphosphane)]-chromium(0) 3. 3 was isolated in pure state as stable compound; different from 2,3 does not suffer from loss of tellurium at room temperature. 相似文献
16.
The equilibrium Xe + 2Ar has been investigated in the temperature range 150–300 K using a selected ion flow tube appratus. From the temperature variation of the equilibrium constant the standrad enthalpy change for the reaction is determined to be −25 ± 5 kj mol−1 and the dissociation energy of XeAr+ is estimated to be 24 ±5 kj mol−1 (0.25 ± 0.05 eV). At ≈ 150 K the approach to equilibrium is consistent with a rate coefficent of (5 ± 3) × 10−21 cm 6 s−1 for the forward three-body association reaction. 相似文献
17.
Dr. Suranjan De Dr. Hugo E. Gottlieb Prof. Shmaryahu Hoz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(30):6846-6850
The method developed and introduced here enables for the first time (to the authors’ knowledge), a quantitative assessment of the interaction of SmI2 with substrates prior to the electron transfer stage. As a proof of concept, equilibrium constants for some model substrates including carbonyl compounds and aromatic nuclei are reported here. In addition, the first equilibrium constants with some common ligands were also determined. The equilibrium constants range from approximately 0.07 m −1 for diisopropyl ketone to 2500 m −1 for hexamethylphosphoramide (HMPA). It is shown that the data acquired by this method, which is based on the concept of shift reagents, can shed light on the most intimate details of the reaction mechanism, and this method is a useful tool for planning a synthetic process. 相似文献
18.
Tests are described for differentiation between neutral, basic, and acidic amino acids based on the formation of nickel dimethylglyoxime precipitate from an equilibrium mixture containing Ni2+, dimethylglyoxime and Ni2+, dimethylglyoxime-glycine. A highly sensitive and specific test for lysine is described, based on the formation of nickel dimethylglyoxime precipitate in a drop of the equilibrium mixture, by the reaction of the volatile amino aldehyde, produced by the oxidative deamination-decarboxylation of lysine. Other basic amino acids, i.e., arginine and histidine do not interfere, and the test can be applied for lysine in a mixture with other amino acids. 相似文献
19.
The equilibrium of the reaction Cu2++Cu?2 Cu+ has been investigated in cone. solutions of Ca(ClO4)2. The apparent equilibrium constants of this reaction and the formal potentials of the Cu2+/Cu+, Cu2+/Cu and Cu+/Cu redox systems were determined. From these data the hydration numbers of the Cu2+ and Cu+ ions were estimated and the scheme of the reaction studied was proposed and discussed. In addition the equilibrium constants of the reaction Cu2++Cu(Hg)?2 Cu+ were calculated and discussed. 相似文献
20.
I. G. Vasil’eva 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(11):1842-1847
A new methodology is proposed and the phase equilibrium is investigated in the Ln2S3-LnS2 systems, in which the low-temperature behavior of nonstoichiometric phases is controlled by the kinetics of the ordering of defects. It is shown that, under equilibrium conditions, the phase equilibrium in the systems is represented not only by a polysulfide with a wide homogeneity region, but also by several (or one) phases of constant irrational compositions combined in the homologous series LnnS2n?1 (n = 3, 4, 7, 8, and 10). The formation of sulfur vacancies and isolated [S2]2? ions (which compensate the charge) in the anionic S2? layer is the basic mechanism of changing the composition of the members of the series. On the basis of structural data, the possible mechanisms of the ordering of defective LnS2?x polysulfides are examined and it is shown that the formation of stable or metastable phases is a kinetics-controlled process. The role of p s-T-x diagrams in the interpretations of complex structures of metastable phases from the point of view of attainment of the equilibrium state is discussed. 相似文献