Ammonia free energy

When carbon forms four covalent bonds with halogen atoms the second quantum level on the carbon is completely filled with electrons. Most of the reactions of the Group IV tetrahalides require initial donation by a Lewis base (p. 91) (e.g. water, ammonia) which attaches initially to the tetrahalide by donation of its electron pair. Hence, although the calculated free energy of a reaction may indicate that the reaction is energetically favourable, the reaction may still not proceed. Thus we find that the tetrahalides of carbon... 

Let us define the respective basicity by — AG in the gas phase and — AG" in aqueous solution. For discussions concerning the relative strength in basicity of a series of methyl-amines, only the relative magnitudes of these quantities are needed. Thus the free energy changes associated with the protonation of the methylamines relative to those of ammonia are defined as... 

The production of ammonia is of historical interest because it represents the first important application of thermodynamics to an industrial process. Considering the synthesis reaction of ammonia from its elements, the calculated reaction heat (AH) and free energy change (AG) at room temperature are approximately -46 and -16.5 KJ/mol, respectively. Although the calculated equilibrium constant = 3.6 X 108 at room temperature is substantially high, no reaction occurs under these conditions, and the rate is practically zero. The ammonia synthesis reaction could be represented as follows ... 

Free energies of formation suggest that ammonia and ammonium nitrate could be produced spontaneously in... 

Table 6.1 Standard free energy of formation data for ammonia synthesis.

Marchi, M. Sprik, M. Klein, M. L., Calculation of the free energy of electron solvation in liquid ammonia using a path integral quantum Monte Carlo simulation, J. Phys. Chem. 1988, 92, 3625-3629... 

Nitrides and Oxynitrides. Crystalline films of NbN and Nb Nj have been prepared. Electron-diffraction studies showed that the former has a NaCl-type structure and the latter is isomorphous with Ti405 and Ta Nj. " The phase 0-TaN, 0 has been prepared by nitriding Ta metal powder with ammonia gas at 850—1200°C. Although it could not be obtained pure, the phase was characterized by X-ray diffraction studies. The free energy of formation of TajNj has been determined as -272 42 kJ mol and that of TaO, 05N0.95 as -396 21 kJ moP. ... 

The standard reaction free energy, AGr°, is —32.90 kj-mol-1, so the reaction is spontaneous when all the gases are at 1 bar. The reaction does produce ammonia rapidly at first. However, eventually the reaction seems to stop (Fig. 9.1). As the graph shows, no matter how long we wait, no more product is formed. The reaction has reached equilibrium. 

Similar data for the two-component system water-ammonia are also available and complete, because of the use of this system in absorption refrigeration. The data of Scatchard and coworkers are the most recent 24), and are unique among such compilations in that the availability function is tabulated as well as the usual enthalpy, entropy, and Gibbs free energy. These data have been converted to graphical form (charts) by Kohloss and Scott 16) and Bulkley and Swartz 4). Older data, but more complete in the low concentration range, are those of Jennings and Shannon 11). 

Because the free-energy change for any process at constant temperature and pressure is AG = AH — TAS, we can calculate the standard free-energy change AG° for a reaction from the standard enthalpy change AH0 and the standard entropy change AS°. Consider again the Haber synthesis of ammonia ... 

Calculate the free-energy change for ammonia synthesis at 25°C (298 K) given the following sets of partial pressures ... 

Thermodynamics. By correlating thermochemical and electrochemical data for liquid ammonia, it has been possible to estimate thermodynamic functions for a wide variety of ionic species in liquid ammonia at 25 ° C. (22,24). The heats and free energies of formation and entropies (relative to H+) for a few species are given in Table I. These values have been calculated from the data of references 6,19, 20, and 24. 

---