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.