The heats of formation of free CN and free CH 2 , and the relationship between D (CO), D (CN) and D (N 2 )

Abstract

The heats of formation of CN and CH 2 have been calculated by a number of independent methods and shown to have the approximate values —92·5 and —70 kcal. respectively. The former value, which is independent of any data on cyanogen, receives close support from a recent estimate of the lattice energies of sodium and potassium cyanides, and corresponds to ~114 kcal. for the heat of dissociation of C 2 N 2 into two CN radicals. The information provided by the heat of formation of CH 2 regarding the energies involved in the stepwise dissociation of methane furnishes an indication of the true values for the heat of atomization of graphite and the dissociation energy of carbon monoxide. The relation linking D (CO), D (CN) and D (N 2 ) has been recalculated from the derived value for the heat of formation of CN and utilized as far as possible for deciding on the correct dissociation energies. Of the four values which have been proposed for D (CO) and the three values for D (N 2 ), it is possible to eliminate two of the former and one of the latter.