STUART R. GUNN
1386
The Heats of Formation at 25" of the Crystalline Hydrides and Aqueous Hydroxides of Rubidium and Cesium1
by Stuart R. G u n Lawrence Radiation Laboratory, Univesity of Calijornia, Livermore, California (Received October 1 1 , 1966)
The heats of reaction of rubidium and cesium metals and hydrides with water at 25" have been measured. The values determined, in kilocalories per mole, are: M(c) 3001 HzO(1) = RiIOH.3000H20 '/zHz(g), AHoRb = -46.615 0.016, AH"c8 = -48.297 f 0.010; MH(c) 3001HzO(1) MOH.3000HzO Hz(g), AH"Rb = -34.115 f 0.026, AH"cs = -35.382 f 0.022. Slightly revised values for lithium, sodium, and potassium, recalculated from earlier work, are presented.
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The values for the standard heats of formation of the aqueous hydroxides and aqueous ions of rubidium and cesium given in the National Bureau of Standards compilation2 are based on measurements of the heats of hydrolysis of the metals done around the turn of the century. The only modern determination appears to be that of Vorob'yev, Ibragin, and Skuratov13 whose recently reported values are, however, in substantial disagreement with the present work. For the hydrides there is only one calorimetric determination, of CsH4 at rather low precision, although there are several investigations of dissociation pres~ures,s-~for both RbH and CsH, from which heats of formation of varying reliability may be derived. In the present work, the heats of reaction of rubidium and cesium and their hydrides with water have been measured at 25.00" to derive improved thermochemical values for these systems. Apparatus and procedures were similar to those earlier employed in measurements of the heats of hydrolysis of the metals, hydrides, and deuterides of lithium, sodium, and potassium.*
Experimental Section Materials. Cesium, nominally 99.97% pure, was obtained from the Dow Chemical Co., and rubidium, nominally 99.95% pure, from United Mineral and Chemical Corp. Spectrographic analyses of one specimen of cesium indicated
