Activation energy of dissociation

The increase in activation energy of the ortho-para equilibration reaction found by Couper and Eley could be due to an increase in activation energy of dissociation. This implies that the rate of adsorption is rate determining, which is only possible if the surface is sparsely covered or if equilibration occurs by a Rideal mechanism (70). 

Table 8 Kinetic recognition of the size of end groups of bola-amphiphiles by a-CD kt[ ss, first order dissociation rate constant AGjiss, Eyring s free activation energy of dissociation...

Table 1. Rate and Equilibrium Constants for the Reversible Dissociation of Polymeric Alkoxyamines and Low Molecular Model Compounds, Frequency Factors, and Activation Energies of Dissociations...

From the data in Table 11.1 the consistency of A is apparent. If we assume a constant A about equal to the DeBroglie A1 and with relative molar responses of similar compounds in the ECD at the same temperature, the activation energy for thermal electron attachment can be obtained from E x /irc - = RT(ln(Rlef/Rx)). This is only applicable to alkyl chlorides, bromides, or iodides. The activation energy of dissociative reactions for alkylfluorides is too large to be observed in the ECD. 

To study the UAG3T UAG3T quadruplexes kinetics, the authors performed different types of experiments. Addition of an excess of the complementary strand induces a time-dependent formation of the duplex, whose kinetics are related to quadruplex unfolding. A single exponential function perfectly fits the data for each form. At temperature below 40°C, the parallel quadruplex unfolds faster than the antiparallel one. As the antiparallel quadruplex has slightly higher activation energy of dissociation (Eob = +43 kcal moN v.s. +34 kcal mol for the parallel form), kinetic stability is reversed above 40°C. At 37°C, the lifetimes of the two quadruplexes are very close, around 2 h. To study their kinetics of... 

Ukraintseva et al. [154] studied the thermal dissociation processes for clathrates [CuPy4(N03>2] 2G (G= THF and CHCI3) by measuring the wepour pressure and mass loss as a function of temperature. The enthalpies of dissociation are 43 and 51 klmof for the THF and CHC13 clathrates, respectively. The activation energy of dissociation of the THF clathrate is 75 kJ mof by the ASTM E 698 method. 

The combination of single-crystal experiments and DFT calculations provides insight into the structure dependence of the catalytic activity of the metal surface. The chemisorption energy is determined by the electtonic structure (the d-band center), which depends on the surface structure. The activation energy of dissociation is proportional to the chemisorption energy and depends on the geometric structure of the hansition state. 

The effective activation energy for dissociative adsorption depends not only on the activation energies of dissociation of the adsorbed molecule but also on the equilibrium constant of molecular adsorption. Consider the case where the molecu-larly adsorbed species is the majority reaction intermediate (man) in the surface reaction from AR to adsorbed atoms. In order to understand the kinetics of dissociative adsorption, it is essential to realize that surface sites, indicated with, play the role of a reactant in the kinetic equations. The scheme of reactions becomes ... 

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