Cuprous oxide dissociation

It must be borne in mind that the equations (11), etc., hold good only when the condensed phases are chemically homogeneous. Thus Foote and Smith, who determined the dissociation pressure of cuprous oxide ... 

Cupric oxide occurs as the hexagonal tenorite, and also as the rhombic or monoclinic melaconite. According to Slade and Farrow,13 the oxide melts above 1148° C., with partial decomposition into cuprous oxide but Smyth and Roberts14 state that it does not melt with dissociation below 1283° C. Its density is 6-82 to 6-48.15 Its mean specific heat is 0-1420 between 12° and 98° C.,16 and its heat of formation 37-16 Cal.17... 

Cupric oxide dissociates into cuprous oxide and oxygen. Two independent components, cuprous oxide and oxygen, form the system, which] bdow a certain temperature is divided among three phases, solid cupric oxide, solid cuprous oxide, oxygen gas. The system is monovariant, admitting a curve of dissociation tensions. 

Thus, in the same monovariant S3rstem formed of cupric oxide, cuprous oxide, and oxygen, and under the same pressure, two inverse reactions may be observed at a certain temperature, oxidation of curpous oxide at a higher temperature, the dissociation of cupric oxide the dissociation of cupric oxide absorbs heat, the oxidation of cuprous oxide liberates heat. 

Copper is not expected to follow Cabrera-Mott inverse logaridimic kinetics since its oxide is a modifier according to Table 1. In fact, copper follows direct logarithmic kinetics. This was emphasized by results (Table 2) from die analysis of experimental data [5e,9] including the results shown in Figure 2. No attempt is made here to apply the Fehlner-Mott direct logarithmic expression, Eq. (5) above. This is because the evidenee for oxide recrystallization with time is very complex. Onay [39] reported on the formation of multiphase, multilayer scales on copper at 300°C. He foimd that they result from the dissociation of compact cuprous oxide scale that has lost contact with the copper substrate. 

Vaporization of Cuprous Oxide and Other Dissociating Oxides... 

The behavior of dissociating oxides at high temperatures is briefly reviewed. At low pressures the composition of the oxide will correspond to an equilibrium oxygen pressure quite different from the ambient oxygen pressure. Evaporation rate studies on cuprous oxide in various atmospheres show that this oxide dissociates according to CuiO (solid) — 2Cu (gas) + iOi (gas). 

Answer Not in the case of cuprous oxide. There has been surprisingly little done with the simpler transition metal oxides, but those that have been studied have largely been found to dissociate. Oxides such as zinc oxide and stannic oxide dissociate on evaporation to give oxygen, and in the case of stannic oxide a lower oxide of tin. It should be remarked that we were particularly interested in the steady-state evaporation in different ambient atmospheres and this is rather difficult to study mass-spectrometrically. 

The stabilities of the triammino-cuprous halides are almost identical, and the dissociation pressures of the ammino-cupric halides lie very near together.6 The stabilities of hexammino-copper halides is also almost identical the compounds are very readily decomposed by water, and hence do not seem to be formed in aqueous solution. Ammino-derivatives of cupric carbonate, cupric acetate, cupric oxide, and cuprous cyanide and thiocyanate are known. These have the general characteristics of the ammines already described. 

Exactly the same result was obtained when the homopolymers were oxidized at — 25°C with a N,N,N, N -tetraethylethylenediamine-cuprous chloride catalyst, conditions which have been reported to cause coupling of DMP homopolymers solely by rearrangement (14). The NMR spectrum of this polymer is shown in Figure 3, together with the spectra of a mixture of homopolymers and of a random copolymer formed by simultaneous oxidation of the monomers. Apparently, dissociation and redistribution occur often enough to determine the structure of the product in this system, even under conditions that favor coupling of polymer molecules by the rearrangement mechanism. 

In water, the cuprous ion, Cu+, may not exist in appreciable quantities, for it disproportionates (dismutates) into the cupric ion, Cu2+, and copper metal. Certain very slightly dissociated complexes of univalent copper (for example, Cu(CN)J3 and CuClJ") are stable in aqueous solutions and relatively insoluble cuprous compounds (for example, CuCl, and CU2O) may survive in the presence of water if strong oxidizing agents are not also present. The iodide, Cul, and sulfide, Cu2S, are particularly stable. Aside from the instability of the hydrated Cu+ ion, the chemistry of univalent copper is quite similar to that of univalent silver. 

---