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.

Calorimetric Study of Mg 2 Zn 3

Abstract: The thermodynamic properties of Mg2Zn3 were investigated by calorimetry. The standard entropy of formation at 298 K, DfS � , was determined from measuring the heat capacity, Cp, from near-absolute zero (2 K) to 300 K by the relaxation method. The standard enthalpy of formation at 298 K, DfH � 298 , was determined by solution calorimetry in hydrochloric acid solution. The standard Gibbs energy of formation at 298 K, DfG � , was determined from these data. The results obtained were as follows: DfH �(Mg2Zn3) = – 69.80 ± 20 kJ · mol –1 ; DfS � (Mg2Zn3) = – 10.95 ± 1.80 J · K –1 ·m ol –1 ; DfG � (Mg2Zn3) = – 66.55 ± 20 kJ · mol –1 . The electronic contribution to the heat capacity of Mg2Zn3 was found to be similar to pure magnesium, indicating that the density of states in the vicinity of the Fermi level follows the freeelectron parabolic law.

Kinetics of reduction of (Co(NH3)5N3)Cl2 by iron (II) in CTAB/n-heptane/butanol/water reverse micelles

Abstract: The kinetic study of reduction of pentaammineazidocobalt(III) chloride complex by Mohr's salt (ammonium ferrous sulphate) has been carried out in the water pools of cationic reverse micelles of cetyltrimethylammonium bromide (CTAB). The reaction is first order each in Co(III) complex and iron(II) in all water-to-surfactant molar ratios, i.e. at all W values. The observed pseudo first order rate constant (k obs ) versus W plot shows highest rate at W = 8.33. The kinetics has been accounted for by a mechanism involving bimolecular azido-bridged inner-sphere intermediate complex formation between Co(III) complex and iron(II). The significant increase of rate in reverse micellar media as compared to that in aqueous medium is due to the lower micropolarity of the water pool and bound state of reactants in this reverse micellar media, both facilitating the intermediate formation. The activation parameters (standard enthalpy of activation, ∇ ‡ H° and standard entropy of activation, ∇‡S°) of the reaction at different W values have been calculated which corroborate the kinetics of the reaction.

Solubility of Hydrogen in Palladium-Yttrium-Silver Alloys.

Abstract: Thermodynamic quantities for absorption of hydrogen by Pd95–xYxAg5 solid solution alloys with up to x = 6.3 at.% Y have been determined from measurements of pressure-composition isotherms at temperatures between 273 K and 473 K and hydrogen pressures up to 1000 Torr. The hydrogen absorption characteristics have been compared with those of the previously reported Pd–Ag and Pd–Y binary alloys. The relative partial molar enthalpy, ΔHH0, at infinite dilution of hydrogen in Pd95–xYxAg5 alloys increases in exothermicity with increasing Y content from that of Pd–5.0 at.% Ag, almost parallel to that in Pd–Y binary alloys. The relative partial molar entropy, ΔSH0, at infinite dilution in the ternary alloys decreases with Y content from that of Pd–5.0 at.% Ag alloy. The hydrogen solubility behavior at low hydrogen concentration in the Pd–Y–Ag alloys under a “constant volume” condition can be described as due to mainly the strong H–Y attractive pair interaction in the Pd host lattice. The stability of β-hydride and hydrogen concentration at αmax phase boundary increase following alloying with Y from that of Pd–5.0 at.% Ag alloy, respectively, and the changes in the properties with Y content are similar to that in Pd–Y binary alloys.