The Profound Unravelling of Equilibrium Thermodynamics and Arrhenius First-Order Kinetics in Relation to Metal Hydride Desorption Reactions

<div> <p>Approaching the entanglement problem of kinetics with thermodynamics in reversible metal hydride desorption reactions by means of a hyperbola template such as the Michaelis-Menten curve renders a closed solution for their unravelling possible, revealing profound insight of general significance into both, the structure of the rate-limiting thermodynamic factor and the nature of experiment-specific first-order Arrhenius kinetics. As by-product an alternate method of extreme simplicity for modelling transient behaviour of reversible metal hydride tanks is obtained. This paper concludes a series of works concerned with objectively approaching metal hydride soprtion reaction kinetics.</p></div>

The Profound Unravelling of Equilibrium Thermodynamics and Arrhenius First-Order Kinetics in Relation to Metal Hydride Desorption Reactions

<div> <p>Approaching the entanglement problem of kinetics with thermodynamics in reversible metal hydride desorption reactions by means of a hyperbola template such as the Michaelis-Menten curve renders a closed solution for their unravelling possible, revealing profound insight of general significance into both, the structure of the rate-limiting thermodynamic factor and the nature of experiment-specific first-order Arrhenius kinetics. As by-product an alternate method of extreme simplicity for modelling transient behaviour of reversible metal hydride tanks is obtained. This paper concludes a series of works concerned with objectively approaching metal hydride soprtion reaction kinetics.</p></div>

Single-Route Linear Catalytic Mechanism: A New, Kinetico-Thermodynamic Form of the Complex Reaction Rate

For a complex catalytic reaction with a single-route linear mechanism, a new, kinetico-thermodynamic form of the steady-state reaction rate is obtained, and we show how its symmetries in terms of the kinetic and thermodynamic parameters allow better discerning their influence on the result. Its reciprocal is equal to the sum of n terms (n is the number of complex reaction steps), each of which is the product of a kinetic factor multiplied by a thermodynamic factor. The kinetic factor is the reciprocal apparent kinetic coefficient of the i-th step. The thermodynamic factor is a function of the apparent equilibrium constants of the i-th equilibrium subsystem, which includes the (n−1) other steps. This kinetico-thermodynamic form separates the kinetic and thermodynamic factors. The result is extended to the case of a buffer substance. It is promising for distinguishing the influence of kinetic and thermodynamic factors in the complex reaction rate. The developed theory is illustrated by examples taken from heterogeneous catalysis.

THERMODYNAMICS OF QUERCETIN SOLVATION IN WATER-DIMETHYLSULFOXIDE SOLVENT

The distribution coefficients of quercetin (QCT) in water-dimethylsulfoxide solvents with a content of dimethylsulfoxide from 0.0 to 0.5 mol. fr. were determined by the method of interfacial distribution of the substance between two immiscible phases: aqueous or water-dimethylsulfoxide solution and n-hexane at 298.2 K. The distribution coefficients are less than one, which indicates a better solvation of quercetin in water and a water-dimethylsulfoxide solvent than in hexane. Changes in the distribution coefficients of quercetin are not correlated with a gradual increase in the content of dimethylsulfoxide (DMSO) in the solvent. Using the obtained values of the distribution coefficients, we calculated the changes in the Gibbs energy of re-solvation of quercetin in water-dimethylsulfoxide solvents. The dependence of the Gibbs energy of QCT re-solvation on the solvent composition has an extreme form with a minimum in the range of DMSO concentrations corresponding to 0.3 mol. fr. A comparative analysis of the effect of a water-dimethylsulfoxide solvent on the change in Gibbs energy of re-solvation of quercetin, nicotinamide and nicotinic acid was carried out. In the case of both nicotinamide and nicotinic acid, an extreme change is observed in the Gibbs energy of re-solvation of particles with a maximum in the region with a low content of non-aqueous component XDMSO ≈ 0.1 mol. fr. The main contribution to the weakening of the solvation of nicotinamide and nicotinic acid is due to the enthalpy component, and with increasing concentration of dimethylsulfoxide there is an increase in the contribution of entropy to the change in the Gibbs energy transfer. An extreme change in the Gibbs energy transfer of quercetin suggests that the minimum on the dependence ∆trGº(QCT) = F(χDMSO) is also a consequence of a change in the prevailing thermodynamic factor in the solvate state of quercetin.

Diffusion in Binary Aqueous Solutions of Alcohols by Molecular Simulation

Based on the molecular dynamics method, the calculations for diffusion coefficients were carried out in binary aqueous solutions of three alcohols: ethanol, isopropanol, and tert-butanol. The intermolecular potential TIP4P/2005 was used for water; and five force fields were analyzed for the alcohols. The force fields providing the best accuracy of calculation were identified based on a comparison of the calculated self-diffusion coefficients of pure alcohols with the experimental data for internal (Einstein) diffusion coefficients of alcohols in solutions. The temperature and concentration dependences of the interdiffusion coefficients were determined using Darken’s Equation. Transport (Fickian) diffusion coefficients were calculated using a thermodynamic factor determined by the non-random two-liquid (NRTL) and Willson models. It was demonstrated that for adequate reproduction of the experimental data when calculating the transport diffusion coefficients, the thermodynamic factor has to be 0.64. Simple approximations were obtained, providing satisfactory accuracy in calculating the concentration and temperature dependences of the transport diffusion coefficients in the studied mixtures.