Showing papers on "Standard molar entropy published in 1983"

Heat capacity, relative enthalpy, and calorimetric entropy of silicate minerals; an empirical method of prediction

Abstract: A procedure to estimate the standard molar heat capacity, relative enthalpy, and calorimetric entropy of silicate minerals has been devised and evaluated. These are estimated by summing, in appropriate proportions, fictive molar isobaric heat capacities, relative enthalpies, and entropies evaluated for structural components of the mineral phases such as MgO-4, MgO-6, or MgO-8 where the Mg is in 4-,6-, or 8-fold coordination, respectively. The fictive molar heat capacities and entropies were obtained from a large body of experimental calorimetric data on heat capacity, entropy, and relative enthalpy for minerals. The summation technique has a precision better than2To for heat capacity and relative enthalpy, and 5Vo for entropy, relative to the data base, between 29E and 1500 K. The accuracy of prediction of molar heat capacity and relative enthalpy for mineral phases and specific heat for rocks is expected to be within 3Tousing this technique. The accuracy of prediction of molar calorimetric entropy is expected to be within 5% using this technique. Tables of evaluated coefficients for the structural components of mineral phases are given. Three examples of calculations are given. (1) The estimated heat capacity of an illite is calculated and compared with experimental data which was not used in the evaluation. (2) The estimated relative enthalpy of acmite is calculated and compared with experimental data also not used in the evaluation. (3) The estimated calorimetric molar entropy of an illite is calculated and compared with data not used in the evaluation. In each of these cases, the estimated values deviate less than 2.5Vo from the observed values.

Studies on Aqueous Solutions of Saccharides. I. Activity Coefficients of Monosaccharides in Aqueous Solutions at 25 °C

Abstract: Activity coefficients of isomeric monosaccharides, D-glucose, D-mannose, and D-galactose were determined by isopiestic comparison method at 25 °C Excess partial molar entropy of water (\barSwex) of each monosaccharide solution was negative and the absolute value increased with concentration of solute From the magnitudes of negative \barSwex, it was concluded that the structure making ability among three isomers lies in the order D-glucose>D-mannose>D-galactose

Thermodynamic studies of zeolites; natrolite, mesolite and scolecite

Abstract: Calorimetric measurements have been carried out on specimens of natrolite, mesolite, and scolecite in order to assess the thermodynamic properties of a zeolite series having the same alumino-silicate framework. Low-temperature heat capacity and high-temperature enthalpy increments of natrolite and scolecite were measured by adiabatic and drop-calorimetric techniques. Standard enthalpies of formation at 298.15 K of all three zeolites were determined by solution calorimetry. Thermodynamic functions have been calculated for natrolite to 660 K and for scolecite to 470 K. The heat capacity and standard entropy at 298.15 K have been estimated for mesolite. With reference to zeolitic water, it is concluded that the entropy of water molecules in both natrolite and scolecite is similar to that in ice. A consideration of the X-ray results for the present specimen of natrolite leads to the conclusion that a contribution of about 9.2 J/(mol x K) to the standard entropy is made by the Al-Si disorder in the alumino-silicate framework. The new results allow calculations to be made by which the pressure and temperature effect can be deduced for such equilibria as: natrolite + SiO/sub 2/(aq) = 2 analcime, and natrolite + Ca/sup 2 +/(aq) + H/sub 2/O = mesolite + 2Na/sup +/(aq).more » Results are consistent with observed parageneses in natural occurrences. 21 references, 1 figure, 10 tables.« less

Chemical reactions and the principle of maximal rate of entropy production

Abstract: The author shows that the so-called standard equation of Chemical Kinetics is compatible with the principle of maximal rate of entropy production, but incompatible with Thermodynamics. The principle, on the other hand, is free of this defect and may be used to establish an improved version of the standard equation.

Anodic polarization behaviour of hydride-deuteride electrodes

Abstract: The results of electrochemical measurements performed on hydrogenabsorbing metal electrodes such as LaNi 5− x Al x ( x = 0−1.0), MmNi 4 Al (Mm  misch metal), LaNi 4 Cu and TiNi 0.6 are reported. The equilibrium hydrogen pressure, partial molar enthalpy ΔH and partial molar entropy ΔS of hydride (or deuteride) formation were calculated on the basis of their electrode potentials. The values determined electrochemically agreed very closely with those obtained from the solid-gas equilibrium. The current is strongly governed by the diffusion process at a large anodic polarization of the hydride-deuteride electrodes. The experimental current-overpotential curves are discussed on the basis of electrode and diffusion theory. In the case of hydride electrodes with a small value of − ΔH the diffusion species are mainly the OH − (or OD − ) ions in the electrolyte solution. As the value of − ΔH increases, the activation energy of diffusion becomes larger and the diffusion species become the hydrogen (or deuterium) atoms in the metal.

Monolayers of double long-chain salts on the concentrated sodium chloride solution

Abstract: The surface pressure—area ( π - A ) curves for monolayers of three types of cation-anion double long-chain salts (alkyltrimethylammonium alkanesulfonates, alkyllamonium alkanesulfonates, and alkyllamonium alkanoates) on the concentrated electrolyte solution (i.e., 4.4 M NaCl) were measured at various temperatures by the Langmuir method. Of three types of double long-chain salts, the π - A curves for some of these salts have two transition points. And a marked temperature dependence of the first transition pressure was observed which leads to a large apparent molar entropy change on the phase transition, while a slight temperature dependence was observed for the second transition pressure which leads to a small entropy change on the transition. The apparent molar entropy change on the second transition is lowered by one order in the magnitude compared with the entropy change on the first transition. Judging from the entropy change on the transition, the first transition was assigned to the transition from the expanded state (E phase) to the condensed state (C-I phase) and the second one to the transition from the C-I phase to another condensed state (C-II phase). There exists a triple point on the phase diagram at which three phases (i.e., E, C-I, and C-II) coexist in equilibrium. In this paper, the other transition from the E phase to the C-II phase was observed at the temperature above the triple point. From the data of the apparent molar entropy change, limiting area, and compressibility, the orientation of double long-chain salts in the condensed film was assumed as follows. In the most compressed state of the C-II phase, the double long-chains are probably aligned perpendicular to the water surface. For the C-I phase, in which the limiting area was considerably larger than in the C-II phase, we can imagine the condensed monolayer with the elongated distance between the ionic head groups because of the incorporation of Na + and Cl − ions into the two-dimensional ionic crystal structure with the long chains aligned on the tilt.

Thermodynamic studies on the addition of molecular oxygen to cobalt(II) complexes. Part 1. The cobalt(II)–ethylenediamine–oxygen system in aqueous solution at 25 °C

Abstract: The equilibrium constant for the formation of [Co2(en)4(O2)(OH)]3+(en = ethylenediamine) in 1 mol dm–3 KCI aqueous solution, at 25 °C, has been determined using polarographic oxygen analysis, pH metric, and spectrophotometric techniques. The enthalpy of formation of this complex has been obtained by direct calorimetric measurements. The thermodynamic functions for the addition of O2 to [Co(en)2]2+ in order to form the doubly bridged dicobalt complex [Co2(en)4(O2)(OH)]3+ have been calculated. The enthalpy change is very large, but the stability of the binuclear species with respect to [Co(en)2]2+ is strongly reduced by a large entropy effect which cannot be explained in terms of the value of the partial molar entropy of oxygen in 1 mol dm–3 KCI solution.

Thermal diffusion of lanthanide chlorides

Abstract: The molar entropy (or heat) of transport of aqueous rare earth chlorides at 0.001, 0.01 and 0.1N have been measured by the potentiometric method using the silver, silver chloride thermocell at a mean temperature of 25°C. Our results indicate that the entropy of transport of rare earth chlorides exhibits a two-series, step function type of dependence on ionic radii. Although this is not the usual S-shaped dependence on ionic radii observed in many thermodynamic and transport properties, the Soret data do seem to show that hydration of the heavier rare earth ions may be rather different from the lighter rare earth ions. The concentration dependence of the entropy of transport have also been investigated for LaCl3, SmCl3, and YbCl3. In all cases the experimental limiting slopes agree well with that predicted by theory based on the electrostatic model.

Zeolitic properties of mixed hexacyanoferrates(II): adsorption isotherms and differential heats of adsorption of water vapour

Abstract: The series of mixed hexacyanoferrates M2Zn3[Fe/CN/6]2.xH2O (M=K+, Na+, Cs+) present zeolitic properties. The adsorption water vapour isotherms were determined by TG at 303 K. The differential heats of adsorption of water vapour were measured by microcalorimetry; the molar integral entropy of the sorbed phase was calculated. The data obtained show that (i) the H2O-sorbent interactions are very weak at the beginning of cavity filling, whereas the sorbed molecules exhibit the same mobility as in the vapour phase; (ii) during the filling, the H2O-H2O interactions increase up to a maximum; (iii) close to total filling, the adsorption phenomenon is comparable to a vapour-liquid transition and the sorbed phase has the same molar entropy as that of the liquid phase.

Thermodynamic studies on the addition of molecular oxygen to cobalt(ii) complexes. part 1. the cobalt(ii)-ethylenediamine-oxygen system in aqueous solution at 25°c

Abstract: The equilibrium constant for the formation of [Co2(en)4(O2)(OH)]3+(en = ethylenediamine) in 1 mol dm–3 KCI aqueous solution, at 25 °C, has been determined using polarographic oxygen analysis, pH metric, and spectrophotometric techniques. The enthalpy of formation of this complex has been obtained by direct calorimetric measurements. The thermodynamic functions for the addition of O2 to [Co(en)2]2+ in order to form the doubly bridged dicobalt complex [Co2(en)4(O2)(OH)]3+ have been calculated. The enthalpy change is very large, but the stability of the binuclear species with respect to [Co(en)2]2+ is strongly reduced by a large entropy effect which cannot be explained in terms of the value of the partial molar entropy of oxygen in 1 mol dm–3 KCI solution.