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Lubricants for the Disk Drive Industry
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
Development of new base oil with low viscosity for improved engine efficiency and low vapor pressure for reduced evaporation loss can benefit from the methodology presented in Section 50.3.3.1. Arrhenius plots are generated for the viscosity and vapor pressure of each oil measured as a function of temperature. The slope and intercept of the Arrhenius provide the activation entropy and activation energy. The goal is to design a base oil with an increased flow-activation entropy without increasing the vaporization and flow-activation energies, and minimal change in the vaporization entropy. This can be accomplished experimentally by measuring these thermodynamic properties for series of base oil structures and compositions to see if the design is going in the right direction. Molecular dynamics simulation would be a nice complement to guide the design of the new molecular structures, but that would be pushing the state of the art. See, for example, Morriss and Evans (2007) and Suarez, Diaz, and Suarez (2011).
Some Generalities on the Kinetics of Chemical Reactions
Published in Jean-Louis Burgot, Thermodynamics in Bioenergetics, 2019
Since the first parameters to consider in the transition state theory are the Gibbs energies of activation ∆G*, these ones (by definition of the Gibbs energy) can be decomposed into an enthalpy of activation ∆H* and into an entropy of activation ∆S* (whatever the direction of the reaction is) that is to say; ΔG* = ΔH* − TΔS* and the relation between a Gibbs energy of activation and the corresponding rate constant k becomes: k = Bexp[ − ΔH*/RT]exp[ΔS*/R]
Chemistry and Kinetics of Polyimide Formation
Published in Malay K. Ghosh, K. L. Mittal, Polyimides Fundamentals and Applications, 2018
James M. Sonnett, Thomas P. Gannett
Cyclization kinetics has been most widely studied for thermal imidization of poly(amic acid) films. In a pioneering study, Kreuz and co-workers [25] described the isothermal cyclization of DMAc-based films of PMDA/ODA poly(amic acid) using two different first-order rate equations. The second equation was used in the region above 45% conversion and featured a lower rate constant (k1/k2 ~ 5.4), which reflects the slowing of the reaction due to lower molecular mobility. Through multiple isothermal experiments, the activation energies of the fast and slow portions of the reaction were found to be essentially identical at 26 and 23 kcal/mol. The smaller rate constant is attributed to a smaller entropy of activation. Model amic acids followed first-order reaction kinetics in DMAc to greater than 75 % conversion. A paradox is that other investigators have observed reductions in the cyclization rates of films and powders of polymeric and monomeric amic acids with increasing conversion [75].
Photodegradation and Box-Behnken design optimization for methomyl using Fenton process based on synthesized CuO nanocrystals via facile wet chemical technique
Published in Chemical Engineering Communications, 2021
Maha A. Tony, Patrick J. Purcell, Shehab A. Mansour
Solving Equations (22) and (23) gives the activation enthalpy, ΔH’ = Ea − RT, and the entropy of activation, ΔS’ = (ΔH’−ΔG’)/T, where kB is Boltzmann constant and h is Planck’s constant. The thermodynamic parameters for methomyl oxidation have been estimated accordingly and are shown in Table 5. Examination of Table 5 shows that the positive values of ΔH’ across the temperature range investigated indicate that reaction is exothermic. Moreover, ΔG’ exhibited positive values, which means the process is non-spontaneous at high temperature. This finding could be due to the formation of a well-solvated structure between the methomyl molecules and hydroxyl radicals that is also supported by a negative entropy of activation (Xu and Li 2013).
Pyrolysis kinetics of regional agro-industrial wastes using isoconversional methods
Published in Biofuels, 2019
Alejandra Saffe, Anabel Fernandez, Marcelo Echegaray, Germán Mazza, Rosa Rodriguez
Considering the ∆S values obtained during degradation of the different components present in all of the studied solid wastes, negative values were obtained for most components, except for those contained in the sawdust and stalk (Table 3). The ΔS values varied between −0.24 and 0.06 kJ mol−1 K−1, presenting the lowest value for the decomposition of the lignin in the sawdust, and the highest value for the degradation of cellulose contained in the same waste. ΔS < 0 indicates that the formed activated complex is more structured or ‘organized’ than the initial molecules, so its formation is accompanied by a decrease in the entropy of activation. When ΔS < 0, the process can be characterized as ‘slow’; the material has just passed through some kind of physical or chemical aging process, bringing it to a state near its own thermodynamic equilibrium. In this situation, the material shows little reactivity, increasing the time taken to form the activated complex.
The role of 8-quinolinyl moieties in tuning the reactivity of palladium(II) complexes: a kinetic and mechanistic study
Published in Journal of Coordination Chemistry, 2019
Daniel O. Onunga, Deogratius Jaganyi, Allen Mambanda
From the temperature dependence of k2, Eyring plots of lnversus were constructed. The enthalpy of activation (ΔH≠) and entropy of activation (ΔS≠) were calculated from the slopes and y-intercepts, respectively, from the plots according to Eyring Equation (2) [59], where T and R represent temperature and gas constant, respectively. Representative Eyring plots for the reactions of 4 are presented in Figure 3; similar plots for the reactions of other complexes are shown in Figures S19–S21 while the values of with their respective are summarized in Tables S6–S9 in the Supporting Information (ESI‡). In addition, the calculated activation parameter values are summarized in Table 3.