Manganese Carbonyl: Heat of Formation by Rotating-Bomb Calorimetry

The heat of formation of dimanganese decacarbonyl (Mn/sub 2/(CO)/sub 10/) was determined by combustion calorimetry. A rotating-bomb method was employed, and a solution of nitric acid and hydrogen peroxide was used in the bomb to convert all manganese-containing products of combustion to Mn/sup + +/ ion. The combustion reaction was referred by suitable comparison experiments to an aqueous solution of composition Mn(NO/sub 3/)/sub 2/ . 10.309H/sub 2/O as a product. This procedure also minimized errors in reduction of the data to standard states. The results of the calorimetric experiments gave for the reaction Mn/sub 2/(CO)/sub 10/(c) + 4HNO/sub 2/ (in 16H/sub 2/O) + 6O/sub 2/(g) = 2Mn(NO/sub 3/)/sub 3/ (in 10.309H/sub 2/O) + 10CO/sub 2/(g) + 2H/sub 2/O(liq) the value ..delta..H/sup 0//sub 296.16/ = -777.0 +- 0.8 kcal. The derived value for the heat of formation of solid manganese carbonyl from graphite, oxygen gas and manganese metal, ..delta..Hf/sup 0//sub 296.16/, is -400.9 kcal. mole/sup -1/.