Thermodynamic parameters for reactions

For several reversible reactions, the thermodynamic parameters for reaction in the quasi-free state are given in Table 10.6 using Eq. (10.16) and the reaction scheme (I). Experimental data for AX°(X = G, H, or S) are taken from Holroyd et al., (1975, 1979) and Holroyd (1977), while Table 10.5A provides data on AX r°, except for TMS (vide supra). The chief uncertainty in these calculations is the experimental determination of V0. It is remarkable that all thermodynamic parameters of reaction in the quasi-free state are negative in the same way as for the overall reaction. In particular, the entropy change is relatively large and probably for the same reason as for the overall reaction (Holroyd, 1977). 

The thermodynamic parameters for Reaction (8.2) in the gas phase, as calculated from the JANAF Thermochemical Tables [359aa], are detailed in Table 8.1, and illustrated in Figures 8.3 and 8.4 [1825a]. Further details of this dissociation reaction are given in Sections 5.1.2 and 6.1.4. 

The columns in Table I A AH,A/, and AAG refer to the thermodynamic parameters for reaction (15). In view of the fact that in molecular H2 complexes, the hydrogen molecule is known to undergo relatively free rotation (1) it was initially considered that the small entropy of binding of hydrogen might be due to less restricted motion of the bound molecule. A simpler explanation is that H2, due to its small mass and moment of inertia has less entropy to lose on complexation than does N2. Thus the entropy of reaction (15) is describe by eqn.(16) below ... 

Table 7 Rate and thermodynamic parameters for reaction of halogen-oxygen compounds with metal ions at 25 °C...

TaUe 4 Rate and thermodynamic parameters for reactions of metal-andno-pofy, carboxylate ions with halogens... 

Table 2.1. Rate Constants and Thermodynamic Parameters for Reactions between Metal Ion Complexes at 25°C ...

Z7. The cotr arison of activation parameters for reactions in two different solvents requires consideration of differences in solvation of both the reactants and the transition states. This can be done using a potential energy diagram such as that illustrated below, where A and B refer to two different solvents. By thermodynamic methods, it is possible to establish values which correspond to the enthalpy... 

Kinetic investigation of the reaction of cotarnine and a few aromatic aldehydes (iV-methylcotarnine, m-nitrobenzaldehyde) with hydrogen eyanide in anhydrous tetrahydrofuran showed such differences in the kinetic and thermodynamic parameters for cotarnine compared to those for the aldehydes, and also in the effect of catalysts, so that the possibility that cotarnine was reacting in the hypothetical amino-aldehyde form could be completely eliminated. Even if the amino-aldehyde form is present in concentrations under the limit of spectroscopic detection, then it still certainly plays no pfi,rt in the chemical reactions. This is also expected by Kabachnik s conclusions for the reactions of tautomeric systems where the equilibrium is very predominantly on one side. 

The physical nature of the sulfate complexes formed by plutonium(III) and plutonium(IV) in 1 M acid 2 M ionic strength perchlorate media has been inferred from thermodynamic parameters for complexation reactions and acid dependence of stability constants. The stability constants of 1 1 and 1 2 complexes were determined by solvent extraction and ion-exchange techniques, and the thermodynamic parameters calculated from the temperature dependence of the stability constants. The data are consistent with the formation of complexes of the form PuSOi,(n-2)+ for the 1 1 complexes of both plutonium(III) and plutonium(IV). The second HSO4 ligand appears to be added without deprotonation in both systems to form complexes of the form PuSOifHSOit(n"3) +. ... 

In contrast to the situation observed in the trivalent lanthanide and actinide sulfates, the enthalpies and entropies of complexation for the 1 1 complexes are not constant across this series of tetravalent actinide sulfates. In order to compare these results, the thermodynamic parameters for the reaction between the tetravalent actinide ions and HSOIJ were corrected for the ionization of HSOi as was done above in the discussion of the trivalent complexes. The corrected results are tabulated in Table V. The enthalpies are found to vary from +9.8 to+41.7 kj/m and the entropies from +101 to +213 J/m°K. Both the enthalpy and entropy increase from ll1 "1" to Pu1 with the ThSOfj parameters being similar to those of NpS0 +. Complex stability is derived from a very favorable entropy contribution implying (not surprisingly) that these complexes are inner sphere in nature. 

There is also substantial stabilization of [4+] by electron delocalization from the cyclic a-vinyl group. This is shown by a comparison of the thermodynamic driving force (p Tr lies between —7.8 and —8.5) and absolute rate constant (ks = 1 -6 x 107 s 1) for the reaction of [4+] in 25% acetonitrile in water with the corresponding parameters for reaction of the resonance-stabilized l-(4-methoxyphenyl)ethyl carbocation in water (p Tr = — 9.4and s= 1 x 108 s Table 5). 

The hydrogens within the octahedral olefin-dihydride intermediate are transferred consecutively with overall cis addition, and the rate-determining step (k9) is olefin insertion to give the alkyl- hydride. Kinetic and thermodynamic parameters for nearly all the steps of Fig. 1 have been estimated for the cyclohexene system. Because the insertion reaction is generally believed to require a cis disposition of the hydride and olefin... 

Table 5 lists equilibrium data for a new hypothetical gas-phase cyclisation series, for which the required thermodynamic quantities are available from either direct calorimetric measurements or statistical mechanical calculations. Compounds whose tabulated data were obtained by means of methods involving group contributions were not considered. Calculations were carried out by using S%g8 values based on a 1 M standard state. These were obtained by subtracting 6.35 e.u. from tabulated S g-values, which are based on a 1 Atm standard state. Equilibrium constants and thermodynamic parameters for these hypothetical reactions are not meaningful as such. More significant are the EM-values, and the corresponding contributions from the enthalpy and entropy terms. 

The thermodynamic parameters for the alkane dehydrogenation reaction are calculated for both the pincer and anthraphos iridium(III) complexes. The mechanism of the transfer reaction, and the associative, dissociative and interchange mechanisms for the acceptorless reactions are discussed and compared. As these reactions typically occur at conditions very different from STP, important corrections for high temperature, high reactant (alkane) concentration and low product (H2, olefin) concentration are important. 

It has been suggested that an increase in the coordination number of vanadium from 4 to 5 already takes place in the second protonation step, i.e. when [H2V04] is formed (21). For reactions (1) and (2), however, the protonation constants and thermodynamic parameters are comparable with those reported for P04 and As04 , providing firm evidence that reaction (2) is not accompanied by incorporation of water in the vanadate ion (15, 17). Further, the estimated thermodynamic quantities for reaction (6), AH° = -39 kJ/mol and AS0 = —51 J/(mol K), obtained by extrapolation from the experimental values for reactions (1) and (2) and those for the three protonation steps of P04 and As04 , are not typical of a simple protonation reaction (17). For such a reaction the entropy change is normally a positive quantity often amounting to 100 50 J/(mol K) and the enthalpy... 

From the temperature variation of the equilibrium constant, thermodynamic parameters for the reaction were also obtained. The extent of formation of [Mo(CO)5l]" was found to be cation-dependent, and while equilibrium constants of 39 and 21 atm L moF were obtained for Bu4P and pyH+, none of the anionic iodide complex was observed for Na. Despite this variation, there seemed to be no correlation between the concentration of [Mo(CO)5l]" and the rate of the catalytic carbonylation reaction. It was proposed that [Mo(CO)5] and [Mo(CO)5l] are spectator species, with the catalysis being initiated by [Mo(CO)5]. Based on the in situ spectroscopic results and kinetic data, a catalytic mechanism was suggested, involving radicals formed by inner sphere electron transfer between EtI and [Mo(CO)5]. 

For CFD modeling a detailed chemical mechanism for the relevant gas phase and surface reaction steps is necessary. Due to the difficulty involved in determining kinetic and thermodynamic parameters for the elementary steps, these are often based on empiricism and even guessing. Here, theoretical first-principles methods can be very helpful. 

The kinetic parameters of Zn(II)/Zn(Hg) electrode reaction in aqueous solution containing perchlorate, nitrate, chloride, and bromide ions were measured at different temperatures (5-50°C) [35]. The Arrhenius activation energy and thermodynamic parameters for the Zn(II)/Zn(Hg) system... 

The tonic compound caesium chloride, Cs + CI-, dissolves readily in water to give a solution containing the individually hydrated Cs+ (aq) and Cl-(aq) ions. The thermodynamic parameters for the formation reaction of Cs hCl and for the reaction of its solution in water are ... 

Each group then rotates through all the experiments developed by the class. The course is on thermodynamics and kinetics so the assigned projects cover these topics. A typical set of projects is free energy relationships, activation energy for a reaction, calorimetry, determination of reaction order for a complex reaction, and determination of the thermodynamic parameters for a charge transfer reaction. 

The table demonstrates a good agreement between the thermodynamic parameters of the complexing reactions inside both the model and the real systems. Moreover, the absolute values of the thermodynamic parameters for the corresponding complex-... 

Kinetic and Thermodynamic Parameters for the Reaction of Trisidiiminei Metal(IH)... 

Table 105 Thermodynamic Parameters for the Reaction [NiLopen]2+ + Lcyd [NiLcyol]2+ + (values in kJ mol-1)2714...

Another approach to the study of proteins has been the reaction of silver ions with simpler model compounds, for example di- and tri-peptides.416 The reaction with glycylglycine was first studied in 1951 and the formation constants for 1 1 and 1 2 complexes were determined.403 Thermodynamic parameters for these reactions have since been measured (log 0i = 2.90, logp2 = 5.65, AHfo = -56.9 0.8kjmol"1, ASj32 = -80.5 3 JK"1 mol"1).416... 

The formation of 1 1 complexes between ethylenediamine-N, N1 -diacetic acid (edda) and Zn11 or Cd11 have been studied by calorimetric (AH) and potentiometric techniques.389 Earlier studies had omitted to allow for protonation reactions of the ethanoato groups in the ligand. Thermodynamic parameters for edda lie between those of nitrilotriacetate and triethylenetetra-mine. Edda appears to undergo a slow metal-ion-catalyzed hydrolysis in aqueous acid solution. 

Thermodynamic parameters for many reactions have been evaluated and tabulated in this way. Nevertheless, there has been a quite natural desire to obtain thermodynamic information about single half-reactions, in particular the reaction occurring at the working electrode. In the strictest sense, it is impossible to separate the thermodynamic parameters for a cell reaction into those of its component half reactions" Nevertheless, a procedure has been advanced and evaluated that accomplishes this separation with negligible errors [1]. 

Some interesting conclusions can be drawn from the thermodynamic parameters for base hydrolysis of the MA+ complexes (Table 19). The rate enhancements in the metal ion-promoted reactions arise from more positive values of AS41 and, in general, lower enthalpies of activation. In addition, there is a close correspondence between values of log XMA+ and AG (Figure 5). The general trends in AH and AS in the metal-promoted reactions can be rationalized in terms... 

Thermodynamic parameters for the benzene oxide-oxepine system are calculated at MP4(SDQ)/6-31+G //HF/ 6-31G level of theory. The effect of solvent polarity on the above equilibrium is studied using the isodensity polarized continuum method. Low polar solvents favor the oxepine formation, whereas medium to high polar solvents lead to benzene oxide formation. The transition state for the tautomerization is fully characterized and the activation energies for the forward and reverse reaction are estimated to be ca. 9.5 and 11.0 kcal mol-1, respectively. The solvent polarity exerts a reasonable effect decreasing the activation energies up to 4 kcal mol-1 <2001MI471>. 

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