Enthalpy thermodynamic parameter

The minimization of the free energy in accordance with White-Johnson-Dantzig allows the determination of the composition of the detonation products in equilibrium state. The thermodynamic parameters (enthalpy, entropy, free enthalpy, free energy) of the detonation products can be calculated using functions based on the enthalpy //°-//°. The coefficients c0,. .. c4 can be found in literature J. Chem. Phys 1958, 28, 751 755 Prop., Expl. Pyrotech. 1985,10, 47-52] ... 

As examples for temperature-dependent enantiomer-selective binding of chiral guests to chiral hosts evaluated by determining thermodynamic parameters (enthalpy, entropy) ... 

To obtain a quantitative measure of cation binding to the gramicidin channel, one must determine the enthalpy and entropy for the binding process not just an equilibrium constant at a single temperature. These thermodynamic parameters (enthalpy and entropy) for the binding of cations to the channel entrance have been obtained by using the T1 NMR-competitive binding method. Briefly, this method involves the measurement of the... 

Although the log values for first complexations of lns(l,4,5)P3 with (5,5)-and [(R,R)-35f were nearly identical, the differences in thermodynamic parameters (enthalpy and entropy changes) suggest different binding modes for the two combinations. These results provide important information about the design and synthesis of chemical receptors, sensors, and inhibitors for lns(l,4,5)P3 and related compounds such as Ptdlns(4,5)P2, and for the design of supramolecular complexes using phosphate-metal coordination bonds. 

Thermodynamic parameters (enthalpy, entropy, thermodynamic potential) allows describing various physical, chemical and other processes and explicitly assess the possibility of their flow without vividly using physical models. The application of reliable values of formation enthalpies is required for searching new perspective materials and compounds, assessment of molecule kinetic properties, analysis mechanisms of rocket propellant combustion, etc. [1,2,3],... 

In order to compare the thermodynamic parameters of different reactions, it is convenient to define a standard state. For solutes in a solution, the standard state is normally unit activity (often simplified to 1 M concentration). Enthalpy, internal energy, and other thermodynamic quantities are often given or determined for standard-state conditions and are then denoted by a superscript degree sign ( ° ), as in API", AE°, and so on. 

The results were simple and clear-cut Only the two terms ofa° and Emin were involved for the a-cyclodextrin systems, and the two terms of k and Emin, for (S-cyclodextrin systems. This means that the stabilities of the inclusion complexes are mainly governed by the electronic and steric interactions in a-cyclodextrin systems and by the hydro-phobic and steric interactions in (i-cyclodextrin systems, regardless of the position of the substituents in the phenols. These observations agree well with those by Harata23), who showed that there is no appreciable difference in thermodynamic parameters between cyclodextrin complexes of m- and p-di substituted benzenes and that the contribution of the enthalpy term to the complexation is more significant in a-cyclodextrin systems than in P-cyclodextrin systems, where the inhibitory effect... 

As already mentioned, the enthalpy change A//° involved in an elementary propagation step corresponds to the equilibrium constant S. The parameter a, however, is purely entropically influenced mainly due to the steric restrictions during the formation of a helical nucleus. The determination of a, since it is related to the same power (3n - 2) of s, requires the consideration of the dependence of the thermodynamic parameters on the chain length (Eq. (9 a)). 

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. 

It is now be pertinent to move on to chemical reactions which, as mentioned earlier, are central to the subject of thermochemistry. Metallurgical processes are mostly carried out at constant pressure and, therefore, enthalpy assumes the role of a very important thermodynamic parameter in metallurgical thermochemistry. 

The magnitudes of the thermodynamic parameters, A77 and AS sometimes provide evidence supporting proposed mechanisms of drug decomposition. The enthalpy of activation is a measure of the energy barrier that must be overcome by the reacting molecules before a reaction can occur. As can be seen from Eq. (28), its numerical value is less than the Arrhenius... 

Isoperibolic calorimetry measurements on the n-butanol/water and n-butoxyethanol/water systems have demonstrated the accuracy and convenience of this technique for measuring consolute phase compositions in amphiphile/water systems. Additional advantages of calorimetry over conventional phase diagram methods are that (1) calorimetry yields other useful thermodynamic parameters, such as excess enthalpies (2) calorimetry can be used for dark and opaque samples and (3) calorimetry does not depend on the bulk separation of conjugate fluids. Together, the present study and studies in the literature encompass all of the classes of compounds of the amphiphile/CO ydrocarbon/water systems that are encountered in... 

Papisov et al. (1974) performed calorimetric and potentiometric experiments to determine the thermodynamic parameters of the complex formation of PMAA and PAA with PEG. They investigated how temperature and the nature of the solvent affected the complex stability. They found that in aqueous media the enthalpy and entropy associated with the formation of the PMAA/PEG complex are positive while in an aqueous mixture of methanol both of the thermodynamic quantities become negative. The exact values are shown in Table II. The viscosities of aqueous solutions containing complexes of PMAA and PEG increase with decreasing temperature as a result of a breakdown of the complexes. 

Table 6.1 summarizes the thermodynamic parameters relating to the macrocyclic effect for the high-spin Ni(n) complexes of four tetraaza-macrocyclic ligands and their open-chain analogues (the open-chain derivative which yields the most stable nickel complex was used in each case) (Micheloni, Paoletti Sabatini, 1983). Clearly, the enthalpy and entropy terms make substantially different contributions to complex stability along the series. Thus, the small macrocyclic effect which occurs for the first complex results from a favourable entropy term which overrides an unfavourable enthalpy term. Similar trends are apparent for the next two systems but, for these, entropy terms are larger and a more pronounced macrocyclic effect is evident. For the fourth (cyclam) system, the considerable macrocyclic effect is a reflection of both a favourable entropy term and a favourable enthalpy term. 

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. 

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