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.

Electrochemical Investigation of the Lithium‐Gallium System

Abstract: The thermodynamic properties of the lithium‐gallium binary system have been investigated by the use of electrochemical methods, with special attention being given to the phase . Measurements have also been made of the mass transport parameters in , including the determination of the composition dependence of the chemical diffusion coefficient, the self‐diffusion coefficient, and the enhancement factor. The data on emf vs. composition, obtained by use of the coulometric titration technique at 415°C, show that all three intermediate phases, whose nominal compositions are , , and, have appreciable ranges of stoichiometry. The existence of these three phases was further substantiated by x‐ray diffraction analysis. At 415°C, the constant emf values in the two‐phase regions are 565, 122, 91, and 20 mV with respect to pure liquid lithium, in the order of increasing lithium concentration. Measurements are reported on the temperature dependence of the most gallium‐rich plateau, leading to values of the partial molar entropy and enthalpy of lithium in that two‐phase region. The lithium activity has been found to follow Henry's law in liquid lithium‐gallium alloys and electrochemical measurements of the temperature dependence of the solubility of lithium in liquid gallium confirmed earlier results. The activity of lithium in the vario‐stoichiometric phase lies between and 0.126 at 415°C over a composition range from 44.8 to 56.0 a/o Li. The Gibbs free energy of mixing was determined as a function of composition across the phase and found to have a minimum value of −25.8 kJ/mol at 47.6 a/o Li. The standard Gibbs free energy of formation of all three intermediate phases was evaluated at their nominal stoichiometric compositions; the values are −51, −115, and −62 kJ/mol, respectively. The chemical diffusion coefficient within the phase varies from . On the lithium‐rich side of , the chemical diffusion coefficient increases slightly with increasing lithium concentration. On the lithium‐deficient side of the ideal stoichiometry, the chemical diffusion coefficient increases rapidly as lithium is deleted. After reaching a maximum value at 47.6 a/o Li, it gradually decreases again with further decrease in lithium content. The enhancement factor, which relates the chemical and self‐diffusion coefficients, is also composition dependent. It reaches a maximum value of 56 at the same composition as the peak in the chemical diffusion coefficient and the minimum in the Gibbs free energy of mixing.

Heat Capacity, Transformations, and Thermal Disorder in the Solid Electrolyte RbAg4I5

Abstract: The heat capacity of RbAg4I5 has been measured in an adiabatic calorimeter between 5 and 340°K. The compound undergoes transformations at 121.8 and at 209°K and exhibits a very sizable configurational heat capacity. The latent heat and entropy changes of the apparently first‐order transformation at 121.8°K are 190.9 ± 0.8 cal mole− 1 and 1.568 ± 0.007 cal deg− 1·mole− 1, respectively. The second transformation appears to be of the lambda type. Upper limits to the heat and entropy changes are 225 cal deg− 1 and 1.0 cal deg− 1·mole− 1, respectively. The configurational entropy is 10.81 cal deg− 1·mole− 1 at 300°K. A residual entropy of 2.25 ± 1.6 cal deg− 1·mole− 1 was found. The standard entropy for the compound is 147.07 cal deg− 1·mole− 1. The ΔS°, ΔH°, and ΔG° of formation are 20.55 ± 2.2 cal deg− 1·mole− 1, − 136.2 ± 0.5 kcal mole− 1, and − 142.3 ± 0.1 kcal mole− 1, respectively. The heat capacity is exceptionally high at all temperatures above ∼50°K. This is attributed to a continuously increasing dis...