THE FREE ENERGY OF NITROGEN COMPOUNDS
Journal of the American Chemical Society
No other forms of elementary nitrogen are known to exist except the gas N2 and its liquid and solid modifications. As in the case of oxygen and hydrogen, we shall postpone, for the present, the calculation of the free energy of liquid and solid nitrogen. Undoubtedly, a t very high temperature, nitrogen would dissociate into the monoatomic gas, but it has been shown by Langmuir' that a t 3500' A, a temperature a t which hydrogen is largely monoatomic, nitrogen a t atmospheric pressure shows no
... pressure shows no sign of dissociation, although dissociaton to the extent of 5% would have been noticeable. Concerning a large number of the important compounds of nitrogen, we have information which enables us to calculate their free energies. Of the oxides there is only one, NzO, which enters into no known reversible reaction which permits the calculation of its free energy. In the case of N203 and Nz05 equilibria are known which would permit the calculation of the free energy, but these have not yet been sufficiently studied. Of the compounds of hydrogen and nitrogen only one has been sufficiently investigated, namely, ammonia. Ammonia. 3/2H2 + ' /2Nz = NH3(g).-The equilibrium between ammonia and its elements has been fully studied, chiefly in the laboratories of Haber and of Nernst. The most recent and reliable investigations are those of JQst2 and of Haber and Le Ro~signol.~ The data obtained,by these investigators will be considered after we have obtained the general free energy equation. From the specific heat formulae given by Lewis and Randallj4 H2; C, = 6.50 + 0.00ogT N2; C, = 6.50 + o . o o~o T NH3; C, = 7.5 4o.oo42T AI? = -5 . 5 + 0.00235T In this case the same heat of reaction was found by Thomsen and by Berthelot, namely, AH291 = -12200 cal.; hence AHo = -10700, and AI?" = -10700 + 5 . g T I n T -o . o o 1 1 7 g T~ + IT. The results of the equilibrium measurements of Jost and of Haber and Of the latter measurements Le Rossignol are given in Tables I and 11.