PbO2 apparently requires four stages of decomposition to reach normalPbO . Based on thermogravimetric studies the intermediate products appear to be 5PbO2·4normalPbO , 4PbO2·5normalPbO , and Pb3O4 . Although the first three stages seem irreversible, they too come to a steady state in decomposition, but no recombination takes place. normalΔH° and normalΔS° values have been calculated for the four stages.

Although earlier investigators showed the dissociation of Ag2O to be reversible and equilibrium points had been obtained, there was a range from 191° to 203°that had not been studied. This region has now been studied. From all the data available and heat capacity data normalΔH°298 , normalΔS°298 , and normalΔG°298 have been calculated to be 14.69 kcal, 31.92 kcal, and 5.17 kcal per mol O2respectively, for the dissociation reaction 2Ag2O→4normalAg+O2 .

Oxygen pressures of the pyrolusite form of MnO2 have been determined in a temperature range of 441°–642°C. The dissociation reaction 4MnO2false(normalcfalse)⇄2Mn2O3false(normalcfalse)+O2false(normalgfalse) has been found to reach a steady state in the forward direction; reaction in the reverse direction was exceedingly slow and did not reach a steady state. normalΔH° and normalΔS° for the reaction at 813°K are 37.87 kcal and 51.28 cal/deg, respectively. With little error these values can be used in the equation −4.5756logpO2 false(normalatmfalse)=37,870/T−51.28 to calculate the pressure for any temperature in the above mentioned range. Conversion to 298.15°K resulted in normalΔH°298=38.8 normalkcal and normalΔS°298=52.8 normalcal/normaldeg for the dissociation. The limits of uncertainties are not given here because equilibria were not attained by recombination.

The equilibrium represented by the equation 6Mn203(c) ~ 4Mn804(c, a) O2 has been studied by measuring the equilibrium pressures of oxygen over Mn203-Mn~O4. From the data obtained in the 1132~176 range studied AH ~ and AS ~ were calculated for the reaction at 1200~ to be 41.2 ___ 1.2 kcal and 32.9 • 1.0 cal/deg, respectively. These constants can be used in the equation --4.5758 log pO2 (atm) ----41,200/T-32.9to relate log poe and temperature of the system in the above-mentioned range with no appreciable additional error. A slight extrapolation showed poe ~ 1 arm at 1252~ The above hH and aS values were converted to 298. 15~ and compared with those in the literature. A new entropy 8~ ~ 36.8 cal/deg for Mn304 and a new heat of formation • z --228.7 kcal for Mn203 are indicated from analysis of data in the literature and the present data. This value of entropy of Mn304 is higher by 1.3 cal/deg (roughly Rln2) than the value taken from the literature. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 157.182.150.22