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.

Topological Research on Standard Absolute Entropies, S⊖298, for Binary Inorganic Compounds

Abstract: For predicting the standard entropy of a binary inorganic compound, two novel connectivity indexesmQ,mG and their converse indexesmQ',mG' based on adjacency matrix of molecular graphs and ionic parameters gi, qi were proposed. The qi and giare defined as qi=(1.1+Zi1.1)/(1.7+ni), gi=(1.4+Zi)/(0.9+ri+ri−1), where Zi, ni, ri are the charge numbers, the outer electronic shell primary quantum numbers, and the radii of ionic i respectively. The good Quantitative Structure-Property Relationship (QSPR) models for the standard entropies of binary inorganic compound can be constructed from 0Q, 0Q', 1G, and 1G', by using a multivariate linear regression (MLR) method and an artificial neural network (NN) method. The correlation coefficient r, the standard error s, and the average absolute deviation of the MLR model and the NN model are 0.9905, 8.29 J·K−1·mol−1 and 6.48 J·K−1·mol−1, and 0.9960, 5.37 J·K−1·mol−1 and 3.90 J·K−1·mol−1, respectively, for 371 binary inorganic compounds (training set). The cross-validation by using the leave-one-out method demonstrates that the MLR model is highly reliable from the point of view of statistics. The correlation coefficients, standard deviations and average absolute deviations of predicted values of the standard entropies of other 185 binary inorganic compounds (test set) are 0.9897, 8.64 J·K−1· mol−1 and 6.84 J·K−1·mol−1, and 0.9957, 5.63 J·K−1·mol−1 and 4.18 J·K−1·mol−1 for the MLR model and the NN model, respectively. The results show that the current method is more effective than literature methods for estimating the standard entropy of a binary inorganic compound. Both MLR and NN methods can provide acceptable models for the prediction of the standard entropies of binary inorganic compounds. The NN model for the standard entropies appears to be more reliable than the MLR model.

The formation of silicon nitride from trisilylamine and ammonia

Abstract: Silane gas has been used for three decades as a precursor for plasma enhanced chemical vapour deposition processes but is unsustainable in the longer term due to the extremely hazardous nature of the compound. Alternative precursor materials have been proposed but have proved to be largely incompatible with the chemistry of the deposition process or the requirements of semiconductor process technology. One compound with the chemical and technological potential as a precursor for silicon nitride deposition is trisilylamine. Calculation of the Gibbs free energy change for the formation of silicon nitride from the reaction of trisilylamine and ammonia demonstrates that the reaction IS thermodynamically feasible as is the reaction involving silane with ammonia. The standard molar enthalpy of formation for trisilylamine was obtained from a semiempirical molecular orbital calculation while the standard molar entropy of formation was determined from spectroscopic data in the absence of a calorimetric value. Thermodynamic properties have been calculated for a range of aminated species using semi-empirical methods and entropy vs. molecular weight equations. These species are potential intermediates in a plasma discharge of trisilylamine and ammonia, with their successive combination leading to the deposition of a film of silicon nitride. Thermodynamic values for reactions involving the formation, propagation and termination of radical species of trisily lamine and ammonia have been determined and a mechanism is proposed for the deposition of silicon nitride films by plasma enhanced chemical vapour deposition. These results indicate that there is no thermodynamic barrier to the use of trisilylamine as a precursor with ammonia gas for the plasma enhanced deposition of silicon nitride films.

Thermodynamic properties of NaZr2(AsO4)3

Abstract: The heat capacity C p 0 of crystalline NaZr2(AsO4)3 has been measured in the range 7–650 K using precision adiabatic calorimetry and differential scanning calorimetry. The experimental data have been used to calculate the standard thermodynamic functions of the arsenate: C p 0 , enthalpy H 0(T) − H 0(0), entropy S 0(T), and Gibbs function G 0(T) − H 0(0) from T → 0 to 650 K. The standard entropy of its formation from elements is Δf S 0(NaZr2(AsO4)3, cr, 298.15 K) = −1087 ± 1 J/(mol K).

The standard entropy of transport of potassium chloride in the water methanol system at 298 K

Abstract: Standard entropies of transport, SKCl*0, and transported entropies of the chloride ion, SCl-0, in H2O–CH3OH mixtures at 298 K have been determined from the measurements of initial and steady-state (final) thermoelectric powers of the silver/silver chloride thermocell in the 0.002–0.040 mol kg-1 concentration range. The variations of SKCl*0 and SCl-0 with the composition of the solvent system are discussed in terms of ion–solvent interaction and ion transport across a temperature gradient.