The Heat of Formation of Nitric Oxide and Phosphorus Trioxide

The heat of formation of nitric oxide has been redetermined by burning samples of red phosphorus in nitric oxide and in an equimolecular mixture of nitrogen and oxygen. A varying fraction of the phosphorus consumed by reaction with nitric oxide was converted to phosphorus trioxide; the remainder being converted to the pentoxide. A value of 21.8 kcal per mole was obtained for the heat of formation of nitric oxide at 25°C. A value of −270 kcal per mole was chosen as the best value for the heat of formation of phosphorus trioxide at 25°C.