NOTES
2720
more reactive for promoting the decomposition of CzH, and CZH, than was previously observed.' The reason for this is not at present understood. Reactivity for proiiioting hydrocarbon decomposition of these films closely parallels that of rhodium filnis discussed elsewhere. Conclusions Hydrogen did not appear in the gas phase for the system CzHs-Ir (100 ') ; however, it did during the early stages of the reaction of CZH, with Ir (27') only to be consumed by subsequent surface reactions. Methane was the primary decomposition product. Ethylene underwent rapid (time : std. dev.
3 0 1 0 1 1 1 1.0 1.1
imauriticq it is a~s:inicdthat the silicon was present as ~vhrciidid not react with the nitric acid solution, and that the calcium and magnesium mere present as CaO and 1igO 11 ith heats of solution of - 1700 cal., g. anti --2100 cal. g., respectively. Under these assumptions the correction amounts to less than 0.2 cal./g. and is conscyucntlly ignored. Thus, the heats of solution of t h e euiopiuni sesquioxide in 6 34 ” 0 3 are - - i 9 . 3 i 0.4 ltcai. mole for the cubic form and -75.2 + 0.3 lccal inolc for the inolioclinic form. This gives, for t h e rcactioii
by I. Eliezer Radiochemistry Department7 Soreq Research Establishment, Israel Atomic Energy Commission, Rehovoth, Israel (Receized M a r c h $7, 2964)
A polarized-ion model was recently introduced’ in order to explain the observed extra stabilization of many complexes as compared to the binary (parent) complexes (by “extra” is meant stabilization over aiid above that due to statistical reasons). Two kinds of approximations were made in this treatment : the first was the model itself; the second, various siiiiplifications of the force fields and interactions which should exist in such a model. This second step made possible the derivation of fairly simple formulas convenient for frequent use. No doubt an electrostatic niodel can be considered as a much rougher approximation for energy calculations than an appropriate quantum niechanical forniulation, for instance along the lines suggested by Dunita and Orgel. However, coiisideriiig the very great complexity of such quantum niechanical calculations
Th,Ol(rubic) -+Eu20s(monoclinic)
ae
c’zsri
=
(-79 .5
-r
(-73 2 Thc Jozirnal
oj
(1) Y Marcus and I Fheaer, J . P h y s Chem , 6 6 , 1661 (1962)
0 4) .-
1’: 0.5)=
Physzcat Chemistry
-4.3
f
0.6 k c d j m o l e
( 2 ) J D Dumtz and L E. Orgel, A d i a n . Inorg. Chem Radzochem , 2, 34 (1960)
