Standard molar entropy

About: Standard molar entropy is a research topic. Over the lifetime, 1586 publications have been published within this topic receiving 29886 citations.

Theoretical and experimental study on the effects of particle size and temperature on the reaction kinetics of cubic nano-Cu 2 O

Abstract: The activities, selectivities, and stabilities of nanoparticles in heterogeneous reactions are size-dependent. In order to investigate the influencing laws of particle size and temperature on kinetic parameters in heterogeneous reactions, cubic nano-Cu2O particles of four different sizes in the range of 40–120 nm have been controllably synthesized. In situ microcalorimetry has been used to attain thermodynamic data on the reaction of Cu2O with aqueous HNO3 and, combined with thermodynamic principles and kinetic transition-state theory, the relevant reaction kinetic parameters have been evaluated. The size dependences of the kinetic parameters are discussed in terms of the established kinetic model and the experimental results. It was found that the reaction rate constants increased with decreasing particle size. Accordingly, the apparent activation energy, pre-exponential factor, activation enthalpy, activation entropy, and activation Gibbs energy decreased with decreasing particle size. The reaction rate constants and activation Gibbs energies increased with increasing temperature. Moreover, the logarithms of the apparent activation energies, pre-exponential factors, and rate constants were found to be linearly related to the reciprocal of particle size, consistent with the kinetic models. The influence of particle size on these reaction kinetic parameters may be explained as follows: the apparent activation energy is affected by the partial molar enthalpy, the pre-exponential factor is affected by the partial molar entropy, and the reaction rate constant is affected by the partial molar Gibbs energy.

THE EQUILIBRIUM 2/3Bi(l) + 1/3BiI$sub 3$(g) = BiI(g)

Abstract: S>The equilibrium 2/3 Bi(l) + 1/3 BiI/sub 3/(g) = BiI(g) was studied by a transpirat ion technique over the temperature range 545 to 735 deg and the pressure range 0.1 to 50 mm. The enthalpy change for the reaction was 21 kcal and the standard entropy 16 eu at mid-temperature. An excess pressure of reduced Bi species in the higher pressure range was interpreted as due to the formation of a polymer, Bi/sub n/I/sub n/. (auth)

The magnetothermal properties of substituted (tetraazoporphynato)manganese(III) in aqueous suspension

Abstract: The magnetocaloric effect (MCE), heat capacity, and enthalpy and entropy of magnetization of the high-spin (acetato)(2,3,7,8,12,13,17,18-octa-para-tert-butylphenyltetraazaporphynato)manganese(III) complex in a 6% aqueous suspension were determined microcalorimetrically at 298 K in magnetic fields of 0.1–1.0 T, that is, under the conditions comparable with those used with (2,3,7,8,12,13,17,18-octaethylporphynato)chloromagnanese(III) studied earlier. High-dispersity complex particles were found to have paramagnetic properties. Positive MCE values were obtained. These values grew as magnetic field induction increased. MCE sensitivity to the nature and electronic structure of the aromatic macroring was studied. The presence of aza groups in the structure of the complex decreases the MCE value compared with the porphyrin complex. The specific heat capacity of the complex strongly depended on the magnetic field value; field dependences had a maximum close to 0.3 T. Changes in the ΔSm(H, T) molar entropy part were also extremal and had maxima at 0.3–0.4 T. Prospects for the use of magnetothermal properties in the quantitative determination of thermodynamic characteristics and for revealing trends of changes in the magnetic activity of porphyrin complexes are discussed.