scholarly journals A Transition State Theory Perspective on the Relation of Reversible Metal Hydride First-Order Kinetics to Equilibrium Thermodynamics

2021 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Transition State ◽  
Metal Hydride ◽  
Transition State Theory ◽  
Blind Spot ◽  
State Theory ◽  
Equilibrium Thermodynamics ◽  
Equilibrium Pressure ◽  
First Order ◽  
First Order Kinetics ◽  
System Pressure

In the event of hydrogen desorption from reversible metal hydrides, equilibrium thermodynamics exert a rate-limiting effect: if system pressure reaches equilibrium pressure, the reaction rate becomes zero. This is usually dealt with by an empiric term of either polynomial or logarithmic nature to first-order kinetics. This paper approaches the matter from a transition state theory perspective, combining the classic Eyring-Polanyi equation with insights on reversible metal hydride chemical overpotential for scrutinizing the relation of Arrhenius first-order kinetics to van’t Hoff equilibrium pressure. The outcome, tested for the example of 4 mol % Ti-doped NaAlH<sub>4</sub>, suggests theoretical coherency and provides a method for identifying the factor by which an experiment deviates from ideal first-order kinetics. Adopting Arrhenius-Eyring-Polanyi first-order kinetics as baseline for modelling kinetic behaviour of metal hydride sorption reactions not only covers a blind spot in the Arrhenius approach but creates a standard for result comparability.

scholarly journals A Transition State Theory Perspective on the Relation of Reversible Metal Hydride First-Order Kinetics to Equilibrium Thermodynamics

2021 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Transition State ◽  
Metal Hydride ◽  
Transition State Theory ◽  
Blind Spot ◽  
State Theory ◽  
Equilibrium Thermodynamics ◽  
Equilibrium Pressure ◽  
First Order ◽  
First Order Kinetics ◽  
System Pressure

In the event of hydrogen desorption from reversible metal hydrides, equilibrium thermodynamics exert a rate-limiting effect: if system pressure reaches equilibrium pressure, the reaction rate becomes zero. This is usually dealt with by an empiric term of either polynomial or logarithmic nature to first-order kinetics. This paper approaches the matter from a transition state theory perspective, combining the classic Eyring-Polyani equation with insights on reversible metal hydride chemical overpotential for scrutinizing the relation of Arrhenius first-order kinetics to van’t Hoff equilibrium pressure. The outcome, tested for the example of 4 mol % Ti-doped NaAlH<sub>4</sub>, suggests theoretical coherency and provides a method for identifying the factor by which an experiment deviates from ideal first-order kinetics. Adopting Arrhenius-Eyring-Polyani first-order kinetics as baseline for modelling kinetic behaviour of metal hydride sorption reactions not only covers a blind spot in the Arrhenius approach but creates a standard for result comparability.

scholarly journals A Transition State Theory Perspective on the Relation of Reversible Metal Hydride First-Order Kinetics to Equilibrium Thermodynamics

2021 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Transition State ◽  
Metal Hydride ◽  
Transition State Theory ◽  
Blind Spot ◽  
State Theory ◽  
Equilibrium Thermodynamics ◽  
Equilibrium Pressure ◽  
First Order ◽  
First Order Kinetics ◽  
System Pressure

In the event of hydrogen desorption from reversible metal hydrides, equilibrium thermodynamics exert a rate-limiting effect: if system pressure reaches equilibrium pressure, the reaction rate becomes zero. This is usually dealt with by an empiric term of either polynomial or logarithmic nature to first-order kinetics. This paper approaches the matter from a transition state theory perspective, combining the classic Eyring-Polyani equation with insights on reversible metal hydride chemical overpotential for scrutinizing the relation of Arrhenius first-order kinetics to van’t Hoff equilibrium pressure. The outcome, tested for the example of 4 mol % Ti-doped NaAlH<sub>4</sub>, suggests theoretical coherency and provides a method for identifying the factor by which an experiment deviates from ideal first-order kinetics. Adopting Arrhenius-Eyring-Polyani first-order kinetics as baseline for modelling kinetic behaviour of metal hydride sorption reactions not only covers a blind spot in the Arrhenius approach but creates a standard for result comparability.

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

2021 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Metal Hydride ◽  
Thermodynamic Factor ◽  
Equilibrium Thermodynamics ◽  
Arrhenius Kinetics ◽  
Closed Solution ◽  
Transient Behaviour ◽  
First Order ◽  
First Order Kinetics ◽  
Rate Limiting ◽  
Profound Insight

<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

2021 ◽  
Author(s):  
Roland Hermann Pawelke
Keyword(s):  
Metal Hydride ◽  
Thermodynamic Factor ◽  
Equilibrium Thermodynamics ◽  
Arrhenius Kinetics ◽  
Closed Solution ◽  
Transient Behaviour ◽  
First Order ◽  
First Order Kinetics ◽  
Rate Limiting ◽  
Profound Insight

<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>

Microscopic Interpretation of Arrhenius Parameters

2018 ◽  
Author(s):  
Niels Engholm Henriksen ◽  
Flemming Yssing Hansen
Keyword(s):  
Activation Energy ◽  
Transition State ◽  
Transition State Theory ◽  
Average Energy ◽  
Zero Point ◽  
State Theory ◽  
Exponential Factor ◽  
Quantum Tunnelling ◽  
Microscopic Interpretation ◽  
The Difference

This chapter reviews the microscopic interpretation of the pre-exponential factor and the activation energy in rate constant expressions of the Arrhenius form. The pre-exponential factor of apparent unimolecular reactions is, roughly, expected to be of the order of a vibrational frequency, whereas the pre-exponential factor of bimolecular reactions, roughly, is related to the number of collisions per unit time and per unit volume. The activation energy of an elementary reaction can be interpreted as the average energy of the molecules that react minus the average energy of the reactants. Specializing to conventional transition-state theory, the activation energy is related to the classical barrier height of the potential energy surface plus the difference in zero-point energies and average internal energies between the activated complex and the reactants. When quantum tunnelling is included in transition-state theory, the activation energy is reduced, compared to the interpretation given in conventional transition-state theory.

Bimolecular Reactions, Transition-State Theory

2018 ◽  
Author(s):  
Niels Engholm Henriksen ◽  
Flemming Yssing Hansen
Keyword(s):  
Transition State ◽  
Saddle Point ◽  
Transition State Theory ◽  
Classical Mechanics ◽  
Small Degree ◽  
State Theory ◽  
Reaction Coordinate ◽  
Partition Functions ◽  
Bimolecular Reactions ◽  
Activated Complex

This chapter discusses an approximate approach—transition-state theory—to the calculation of rate constants for bimolecular reactions. A reaction coordinate is identified from a normal-mode coordinate analysis of the activated complex, that is, the supermolecule on the saddle-point of the potential energy surface. Motion along this coordinate is treated by classical mechanics and recrossings of the saddle point from the product to the reactant side are neglected, leading to the result of conventional transition-state theory expressed in terms of relevant partition functions. Various alternative derivations are presented. Corrections that incorporate quantum mechanical tunnelling along the reaction coordinate are described. Tunnelling through an Eckart barrier is discussed and the approximate Wigner tunnelling correction factor is derived in the limit of a small degree of tunnelling. It concludes with applications of transition-state theory to, for example, the F + H2 reaction, and comparisons with results based on quasi-classical mechanics as well as exact quantum mechanics.

Quasiclassical Trajectory and Transition State Theory Studies of the N(4S) + H2↔ NH(X3Σ-) + H Reaction

2002 ◽  
Vol 106 (16) ◽  
pp. 4125-4136 ◽  
Author(s):  
Ronald Z. Pascual ◽  
George C. Schatz ◽  
Gÿorgÿ Lendvay ◽  
Diego Troya
Keyword(s):  
Transition State ◽  
Transition State Theory ◽  
State Theory
Sign in / Sign up

Export Citation Format

Share Document