Constant Pressure Flame Calorimetry With Fluorine II. The Heat of Formation of Oxygen Difluoride.

The heats of the following reactions were measured directly in an electrically calibrated flame calorimeter operated at one atm pressure and 303 °K. OF 2 ( g ) + 2 H 2 ( g ) + 99 H 2 O ( l ) → 2 [ HF ⋅ 50 H 2 O ] ( l ) F 2 ( g ) + H 2 ( g ) + 100 H 2 O ( 1 ) → 2 [ HF ⋅ 50 H 2 O ] ( l ) 1 2 O 2 ( g ) + H 2 ( g ) → H 2 O ( l ) The reactants and products were analyzed for each of the reactions. From these heats we calculated the corresponding heats of formation, as follows: OF 2 ( g ) Δ H f 298.15 ° = + 24.52 ± 1.59 kJ mol - 1 ( + 5.86 ± 0.38 kcal mol - 1 ) HF ⋅ 50 H 2 O ( l ) Δ H f 298.15 ° = - 320.83 ± 0.38 kJ mol - 1 ( - 76.68 ± 0.09 kcal mol - 1 ) H 2 O ( l ) Δ H f 298.15 ° = - 285.85 ± 0.33 kJ mol - 1 ( - 68.32 ± 0.08 kcal mol - 1 ) The uncertainties indicated are the estimates of the overall experimental errors. The value of the average O - F bond energy in OF2 was calculated to be 191.29 kJ mol-1 (45.72 kcal mol-1).