Composition and heat of combination of a double oxide of chromium and sodium

Abstract
The reactions of sodium oxide and sodium vapour with chromium and chromium sesquioxide are studied at 500–600 °C. The only double oxide stable in contact with chromium and liquid sodium is NaCrO2. X-Ray powder photographs of this compound are analysed. The standard enthalpy of combination of NaCrO2 from its constituent oxides is found by direct measurement: ΔH°298=–24·24 ± 0·24 kcal mol–1(–101·4 ± 1·0 kJ mol–1). Calorimetric solution measurements in hydrochloric acid at 110° C on a sample containing this double oxide with metallic chromium lead to a similar value.

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