Solid decomposition pressure, calculation

All the partial pressures calculated from the equilibrium constants assume unit activity for the condensed-phase components. This assumption is good when they are solid. Above the melting points of the salts, however, continued decomposition of the salt will result in a solution containing dissolved oxide and the partial pressures will depend on the melt composition, and will therefore change as the decomposition proceeds. Because of the form of Kt, the partial pressure calculation will be worst for small oxide concentrations. An examination of the various tables shows that 02 and NO are the major products of nitrate decomposition, the concentration of N02 being rather minor. This results from the fact that the equilibrium 2 N02 = 2 NO + 02 lies to the right for low pressures. 

AjH (WCl, cr, 298.15 K) -105.9 kcal mol" is calculated from A H (298.15 K) - 58.9 kcal mol" for 3 WCl (cr) - WClgCcr) Clg(g). The value of A H (298,15 K) is calculated by the 3rd law method from decomposition pressure data in the temperature range from 354 C to 436 C reported by Shchukarev et al. (1,). The 2nd law, A H (298.15 K) - 73.6+7.9 kcal mol" and the 3rd law drift is -24 12 cal mol" which would correspond to a total entropy discrepancy of -8 4 cal K mol" per mole of WCl. This entropy discrepancy is probably within the combined uncertainty of the data and the estimated entropies for the three species. Shchukarev et al. (2) have shown that decomposition pressures are essentially independent of the composition in the solid phase until WCl (cr) is almost completely decomposed to WClgCcr). This is consistent with the assumption of solid phase activities of unity which we have used In the equilibrium analysis. 

The heat of decomposition (238.4 kJ/mol, 3.92 kJ/g) has been calculated to give an adiabatic product temperature of 2150°C accompanied by a 24-fold pressure increase in a closed vessel [9], Dining research into the Friedel-Crafts acylation reaction of aromatic compounds (components unspecified) in nitrobenzene as solvent, it was decided to use nitromethane in place of nitrobenzene because of the lower toxicity of the former. However, because of the lower boiling point of nitromethane (101°C, against 210°C for nitrobenzene), the reactions were run in an autoclave so that the same maximum reaction temperature of 155°C could be used, but at a maximum pressure of 10 bar. The reaction mixture was heated to 150°C and maintained there for 10 minutes, when a rapidly accelerating increase in temperature was noticed, and at 160°C the lid of the autoclave was blown off as decomposition accelerated to explosion [10], Impurities present in the commercial solvent are listed, and a recommended purification procedure is described [11]. The thermal decomposition of nitromethane under supercritical conditions has been studied [12], The effects of very high pressure and of temperature on the physical properties, chemical reactivity and thermal decomposition of nitromethane have been studied, and a mechanism for the bimolecular decomposition (to ammonium formate and water) identified [13], Solid nitromethane apparently has different susceptibility to detonation according to the orientation of the crystal, a theoretical model is advanced [14], Nitromethane actually finds employment as an explosive [15],... 

The explosive decomposition of the solid has been studied in detail [6], The effect of moisture upon ignitibility and explosive behaviour under confinement was studied. A moisture content of 3% allowed slow burning only, and at 5% ignition did not occur [7], Thermal instability was studied using a pressure vessel test, ignition delay time, TGA and DSC, and decomposition products were identified [8], The presence of acyl chlorides renders dibenzoyl peroxide impact-sensitive [9], There is a further report of a violent explosion during purification of the peroxide by Soxhlet extraction with hot chloroform [10], Residual traces of the peroxide in a polythene feed pipe exploded when it was cut with a handsaw [11]. The heat of decomposition has been determined as 1.39 kJ/g. The recently calculated value of 69° C for critical ignition temperature coincides with that previously recorded. 

To our knowledge, the question of the standard state corrections in DSC experiments has never been addressed. These corrections may in general be negligible, because most studies only involve condensed phases and are performed at pressures not too far from atmospheric. This may not be the case if, for example, a decomposition reaction of a solid compound that generates a gas is studied in a hermetically closed crucible, or high pressures are applied to the sample and reference cells. The strategies for the calculation of standard state corrections in calorimetric experiments have been illustrated in chapter 7 for combustion calorimetry. 

Figure 11.19 Axiai pressure profiie for the barrier screw. Sections of the screw at zero pressure are partiaiiy fiiied with resin and are a iocation for the decomposition of the resin. The solid line in this figure was caicuiated using the methods described previousiy, and the dashed line represents the expected pressure profile and was not calculated...

Two violent pressure-explosions occurred during preparations of dimethylsulfinyl anion on 3—4 g mol scale by reaction of sodium hydride with excess solvent. In each case, the explosion occurred soon after separation of a solid. The first reaction involved addition of 4.5 g mol of hydride to 18.4 g mol of sulfoxide, heated to 70°C [1], and the second 3.27 and 19.5 g mol respectively, heated to 50°C [2]. A smaller scale reaction at the original lower hydride concentration [3], did not explode, but methylation was incomplete. Explosions and fire occurred when the reaction mixture was overheated (above 70°C) [4]. Reaction of 1 g mol of hydride with 0.5 1 of sulfoxide at 80°C led to an exotherm to 90°C with explosive decomposition [5]. These and similar incidents are explicable in terms of exothermic polymerisation of formaldehyde produced from sulfoxide by reaction with the hydride base [6]. The heat of reaction was calculated and determined experimentally. Thermal decomposition of the solution of hydride is not very violent, but begins at low temperatures, with gas evolution [7]. 

Equilibrium constants for (1), (3), and (4) have been listed. Ag20 is quite unstable above 400 K and hence reactions (1) and (4) are not in equilibrium for reasonable pressures of 02. Below 500 K, P(02) is fixed by reaction (4). P(N02) and P(NO) can then be calculated from Kh K3, and K4. Qualitatively, decomposition is negligible in the solid state, but becomes appreciable at 30 to 40°C above the melting point.110... 

A sample of solid ammonium chloride was placed in an evacuated container and then heated so that it decomposed to ammonia gas and hydrogen chloride gas. After heating, the total pressure in the container was found to be 4.4 atm. Calculate Kp at this temperature for the decomposition reaction... 

AH° for this reaction is 79.14 kj/mol in the temperature range of 25°C-125°C. Given that the partial pressure of carbon dioxide in equilibrium with pure solid silver carbonate is 6.23 X 10 3 torr at 25°C, calculate the partial pressure of C02 necessary to prevent decomposition of Ag2C03 at 110.°C. 

At a certain elevated temperature the total pressure of the gases NH3, CO2, and H2O generated by the decomposition of, and at equilibrium with, pure solid ammonium carbonate is 0.400 atm. Calculate the equilibrium constant for the reaction considered. What would happen to PnHj and Pcoj if PhiO were adjusted by external means to be 0.200 atm without changing the relative amounts of NH3(g) and COzlg) and with (NH4)2C03(s) still being present ... 

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