Mercury thermochemical data

The available kinetic and thermochemical data are summarized in Table 7. Based on the approximate equality of E and D1+D2 and on the magnitude of the frequency factor, Billinge and Gowenlock98 would place dimethyl mercury, di-B-propyl mercury, di-isopropyl mercury (above 230 °C) and (on the basis of the frequency factor only, since thermochemical data are not available) di-n-butyl mercury in class II (simultaneous rupture into mercury and two alkyl radicals). If the high frequency factors are simply due to a general softening of the vibrations in the activated state, then in the case of di-isopropyl mercury D2 — 0, while for dimethyl and di-B-propyl mercury D2 is small but finite (2-3 kcal.mole" ). However, within the limits of experimental error all of these alkyls for which thermochemical data are available may have E = Dl+D2, and thus all may belong to class II. At the same time it must be noted that some metal alkyls which are... 

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... 

The physical properties of bismuth, summarized ia Table 1, are characterized by a low melting poiat, a high density, and expansion on solidification. Thermochemical and thermodynamic data are summarized ia Table 2. The soHd metal floats on the Hquid metal as ice floating on water. GaUium and antimony are the only other metals that expand on solidification. Bismuth is the most diamagnetic of the metals, and it is a poor electrical conductor. The thermal conductivity of bismuth is lower than that of any other metal except mercury. 

Relatively few rate constants are available for the alkyl homolysis reactions mainly because clean sources of the alkyl radical have proved difficult to find. Consequently, the data are not always reliable, but some check is available [64, 65] from thermochemical and kinetic data for the reverse reaction. Direct photolysis of azo-compounds and mercury-photosensitized decomposition of alkanes have so far provided the most reliable (although old) data [64]. For good results, the method depended on precise product analysis in the early stages of reaction, with equation (1.9) used to determine where Rabs and Rr r are the initial rates of formation... 

The thermodynamics of this reaction can be calculated using standard enthalpy and entropy of formation data in M.W. Chase, Jr., MST-JANAF Thermochemical Tables, fourth edition. Journal of Physical and Chemical Reference Data, Mono aph 9, 1998 (see also the NIST Website at http //nist.gov). For a metal having weaker affinity for oxygen, such as in mercury(II) oxide, both enthalpy and entropy favor this reaction. For a metal having somewhat stronger affinity, as in copper(ll) oxide, enthalpy disfavors the reaction but is overwhelmed by entropy. 

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