Thermochemical data at

To be consistent the value of E2 should be corrected to constant pressure so that it represents AH for the process involved (flow system studies and static system work with excess inhibitor are essentially constant pressure experiments). Then D < E < D+RT. In the present work a reasonable estimate gives D — E—0J = 57.0 kcal.mole-1. Similarly, D2+D2 should be corrected to 0 °K, giving an estimated value of 59.0 kcal.mole-1. This gives D2 = 2.0 kcal.mole-1. Such corrections are normally within the limits of experimental error, so that experimental values of E are associated directly with dissociation energies, and thermochemical data at 25 °C are used. 

The mean bond dissociation energies (E ) given in Table 12 are based on thermochemical data at 25 C19. Unless previously discussed, the heat of formation of the metal alkyl used is that given by Long60. The higher values of E and D2 for dimethyl mercury are obtained when Long s recommended value for the heat... 

These results follow from thermochemical data at 350-370 K given in Ref. 277. 

Table 6.8. Thermochemical data at 1473K relative to the Cu/NiO system (Eustathopoulos and Drevet 1994).

The molecule methylamine (CH3NH2) can act as a monoden-tate ligand. The following are equilibrium reactions and the thermochemical data at 298 K for reactions of methylamine and en with Cd " (aq) ... 

Fig. 57. Stilbite, heulandite, laumontite. p-T diagram of stilbite, heulandite, and laumontite [01K2]. The solid curve represents the equilibrium stilbite = heulandite + H2O calculated from thermochemical data at/ totai = P-n o Dashed lines represent pressures at 1 and 2 kbar. The thin line represents the reaction heulandite = laumontite + 3 quartz determined by [87C1] the metastable extension is depicted as a dashed curve. The solid curve with symbols stands for the equilibrium stilbite = laumiontite + 3 quartz + H2O [71L1]. The invariant point is indicated [87C1].

Thermochemical Data. Equilibrium considerations significantly limit alcohol yield at low pressures in the vapor-phase process (116). Consequently, conditions controlling equilibrium constants have been determined and give the following relation, where Tis in K (116,117) ... 

Boron Monoxide and Dioxide. High temperature vapor phases of BO, B2O3, and BO2 have been the subject of a number of spectroscopic and mass spectrometric studies aimed at developiag theories of bonding, electronic stmctures, and thermochemical data (1,34). Values for the principal thermodynamic functions have been calculated and compiled for these gases (35). 

Thermodynamic calculations for reactions forming carbon disulfide from the elements are compHcated by the existence of several known molecular species of sulfur vapor (23,24). Thermochemical data have been reported (12). Although carbon disulfide is thermodynamically unstable at room temperature, the equiHbtium constant of formation increases with temperature and reaches a maximum corresponding to 91% conversion to carbon disulfide at about 700°C. Carbon disulfide decomposes extremely slowly at room temperature in the absence of oxidizing agents. 

The absorption wavelengtlrs quoted here are for the complete dissociation of these molecules to the atoms in their ground state. The thermochemical data also show that a temperature of nearly 4000 K is requhed before the atomic oxygen concentration is equal to that of molecular oxygen, and almost 7000 K for the nitrogen atom population to be equal to the molecular nitrogen concentration, at one atmosphere pressure. 

Don t be overly alarmed by the large maximum errors for many model chemistr and the rather poor results in general. It is not surprising that these methods are ve inaccurate at predicting thermochemical data. It is because of the knov shortcomings of existing methods that the compound methods to be discussed in t next section were developed. 

Standard-State Enthalpy Changes (AH°). To expedite calculations, thermochemical data are ordinarily presented in the form of standard-state enthalpy changes of the system AH°(T,P), with the requirement that materials start and end at the same temperature (T) and pressure (P) and in their standard states of aggregation, i.e.,... 

Almost all of the directly measured thermochemical data for the sulfoxides, sulfones, sulfites and sulfates are due to the work of Busfield and Mackle and their coworkers at the University of Leeds and The Queens University, Belfast1-14. This work involved measurement of enthalpies of combustion, fusion and vaporization. It is the basis of the subsequent compilations of Benson and coworkers15, Cox and Pilcher16 and Pedley, Naylor and Kirby11. The data given by the latter are used as the basic data set in the present work. Corrections and omissions are noted in the next section. Data on additional compounds were sought by searching the IUPAC Bulletin of Thermochemistry and Thermodynamics for the years 1980 198318, and by searches of Chemical Abstracts. 

Most thermochemical data are reported for 25°C (more precisely, for 298.15 I<). Temperature is not part of the definition of standard states we can have a standard state at any temperature 298.15 K is simply the most common temperature used in tables of data. All reaction enthalpies used in this text are for 298.15 K unless another temperature is indicated. 

The variations in Fe and Mg contents of the 14 A Fe-chlorite-14 A Mg-chlorite solid solution are considered here. However, structural formulae for chlorite are not as simple as those considered here. As mentioned by Walshe and Solomon (1981), Stoesell (1984), Cathelineau and Nieva (1985) and Walshe (1986), chlorite solid solution may be represented by six components, and accurate thermochemical data on each end-member component at the hydrothermal conditions of concern are necessary to provide a far more rigorous calculation of the equilibrium between chlorite and hydrothermal solution. However, the above argument demonstrates that the composition of chlorite is a highly useful indicator of physicochemical conditions of hydrothermal solution and extent of water-rock interaction. 

From (1-79) it is clear that the Hg content of electrum is related to /sj and A l-vg. Using the thermochemical data for reaction (1-78) by Barton and Skinner (1979), isoactivity lines for Hg in electrum may be drawn on a log/sj-temperature diagram (Fig. 1.175). At a given temperature, the activity of Hg in electrum increases with a decrease in /sj. Therefore, the /sj for the mercurian gold of the Tsugu deposit is inferred to be relatively low. 

The relationship between the iron content of stannite in equilibrium with sphalerite and pyrite or with sphalerite and pyrrhotite was derived based on thermochemical data by Scott and Barnes (1971), Barton and Skinner (1979) and Nakamura and Shima (1982). These types of deposits are skam-type polymetallic (Sn, W, Cu, Zn, Pb, Au, Ag) vein-type and Sn-W vein-type deposits. As shown in Fig. 1.181, the /s -temperature range for each type of deposits is different at a given temperature, /sj increases from Sn-W vein-type through skam-type to polymetallic vein-type deposits. It is interesting to note... 

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