Carbon monoxide energetics

Let us now consider the reduction of a metal oxide by carbon which is itself oxidised to carbon monoxide. The reaction will become energetically feasible when the free energy change for the combined process is negative (see also Figure i.i). Free energies. 

Reference to Figure 3.4 shows that the reduction is not feasible at 800 K. but is feasible at 1300 K. However, we must remember that energetic feasibility does not necessarily mean a reaction will go kinetic stability must also be considered. Several metals are indeed extracted by reduction with carbon, but in some cases the reduction is brought about by carbon monoxide formed when air, or air-oxygen mixtures, are blown into the furnace. Carbon monoxide is the most effective reducing agent below about 980 K, and carbon is most effective above this temperature. 

For intermediate temperatures from 400-1000°C (Fig. 11), the volatilization of carbon atoms by energetic plasma ions becomes important. As seen in the upper curve of Fig. 11, helium does not have a chemical erosion component of its sputter yield. In currently operating machines the two major contributors to chemical erosion are the ions of hydrogen and oxygen. The typical chemical species which evolve from the surface, as measured by residual gas analysis [37] and optical emission [38], are hydrocarbons, carbon monoxide, and carbon dioxide. 

Energetics are size-reduced and mixed with concentrated nitric acid and silver nitrate to form a slurry. The slurry is mixed with Ag2+ from the electrochemical cells to oxidize the energetic material, forming carbon dioxide, nitrogen oxides, water, inorganic salts, and carbon monoxide. 

The energy required to dissociate the acetone molecule into two methyl radicals and a molecule of carbon monoxide may be calculated from thermocheinical data and amounts to 89 kcal. mol.-1. It would be energetically possible, therefore, for a photodecomposition of type B to occur,... 

The lowest excited triplet states of a-dicarbonyl compounds are considerably less energetic than those of simple carbonyls. For instance the energy of the vibrationally relaxed triplet of glyoxal is 55 kcal,366 as compared to 72 kcal for formaldehyde. Irradiation of glyoxal at 4358 A populates the lowest vibrational levels of the first excited singlet, 30% of which fluoresce and 70% of which cross over to the triplet manifold.388 Almost all of the triplet molecules then decompose to formaldehyde and carbon monoxide, the phosphorescence yield being only 0.1%. 

A second type of cluster emission involves molecular species which can be as simple as carbon monoxide or as complicated as the dodecanucleotide mentioned above. In the first case, the CO bond strength is 11 eV, but the interaction with the surface is only about 1 eV. Calculations indicate that this energy difference is sufficient to allow ejection of CO molecules, although 15 percent of them can be dissociated by the ion beam or by energetic metal atoms (6). For such molecular systems it is easy to infer the original atomic configurations of the molecule and to determine the... 

Solution Carbon monoxide has a small electric dipole moment (approx 0.1 Debye), which gives the molecules an energetically preferred orientation as T — 0. However, this dipole moment is so small that the preference is not appreciable until very low temperatures, and the random orientation of the molecules (the dipole has equal probability of pointing in one direction or its opposite) remains as the temperature is lowered. For a mole of CO, each molecule can point in either of two directions and there are 2Na configurations that are about equally probable. This model predicts a residual entropy of... 

There are many ways in which small metal particles can be created and examined (Section 3.2). When the gold particles are supported, the first step is to determine their mean size and size distribution for this there is no real substitute for transmission electron microscopy (TEM). The various energetic and electronic properties then need to be examined, and the bases of the available experimental techniques will be briefly rehearsed in Section 3.3. Of particular interest is the point at which the change from metallic to nonmetallic behaviour occurs as size is decreased, because this corresponds very roughly to the point at which catalytic activity (at least for oxidation of carbon monoxide) starts to rise dramatically. Relevant experimental results and theoretical speculations are reviewed in Section 3.4. 

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