Static-bomb calorimetry

The energy of the process occurring in a combustion bomb is not identical to the energy of combustion required for thermodynamic calculations, in 

Premier Rapport de la Commission Permanente de Thermochimie, Union Internationale de Chimie, Paris, 1934. 

A semi-micro bomb has been used in conjunction with an isothermal phase-change calorimeter (diphenyl ether) and a standard error of 0.01 per cent has been obtained in the combustion of 150 mg samples of benzoic acid.  

Many other compounds have been burnt in static-bomb calorimeters with some success, but the knowledge concerning the final state is frequently inadequate and the result therefore uncertain. Thus, for example, boron trialkyls and carboranes can be burnt to yield CO2, HgO, and H3BO3, with only traces of side reactions or of incomplete combustion, but it has to be assumed that a saturated aqueous solution of boric acid is produced 

One of the chief difficulties associated with moving-bomb methods is that many of the physical properties necessary for rigorous evaluation of the Washburn correction to standard states are unknown. The relatively large volume of solution used in the bomb (10 to 60 cm ) means that the energy of solution of carbon dioxide is appreciable, thus in the combustion of organofluorine compounds in the presence of 10 cm of water it is typically 

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Because of the controversy surrounding the use of static-bomb calorimetry for determining enthalpies of formation of organogermanium compounds1,2, the reliability of most data in Table 1 cannot be fully assessed. It is, however, possible to discuss generally some of the results. 

Thermochemical parameters of some unstable nitrile oxides were evaluated using corresponding data for stable molecules. Thus, for 2,4,6-trimethylbenzo-nitrile N-oxide and 2,4,6-trimethoxybenzonitrile N-oxide, the standard molar enthalpies of combustion and sublimation at 298.15 K were measured by static-bomb calorimetry and by microcalorimetry, respectively, this made it possible to derive the molar dissociation enthalpies of the N—O bonds, D(N—O) (17). 

How can we assess the thermochemical data presented in Table 1 Many were obtained by static-bomb calorimetry. Regrettably, this technique is clearly unsuitable to deal with these substances due to the ill-defined composition of the combustion products (see the discussion in References 13 and 28). The formation of nonstoichiometric oxides upon combustion all but precludes the experimental rigor demanded of the combustion calorimetrist. This fact, by itself, allows us to question the reliability of the values shown for all of the trialkyl compounds and for triphenylantimony. Although the results for triphenylbismuth found by static and rotating-bomb calorimetry overlap within their error bars, this has been suggested to be fortuitous ... 

Enthalpies of formation have been determined for about 70 organotin compounds, principally by static bomb calorimetry, and are listed in the reviews by Pilcher and Skinner,77 Tel noi and Rabinovich,78 Harrison,79 and Simoes, Libman, and Slayden.80-81 The enthalpies of formation of the radicals of Mc, Sn Et3Sn , and BusSn" have been measured to be AH° (g) = 130 17, 99.7 17.6, and -36 kJ mol-1, respectively,80 (that for Bu3Sn by photoacoustic calorimetry) and from these values and the enthalpies of formation of the organotin compounds, bond dissociation enthalpies, D(M-L), for the reaction 2-6 can be derived from equation 2-7. 

Davies et al. 37) studied the combustion of tin tetraalkyls by static bomb calorimetry, and found that virtually complete combustion can be attained. Analysis of the bomb gases after combustion showed that combustion of the carbon content was from 99.8-100% complete, and the solid combustion product was shown to be Sn02, only small amounts of unburned tin remaining admixed with it. Davies et al. obtained the results given in the table. 

Long and Sackman (107) investigated the combustion of MeaP by static bomb calorimetry, and found that the main product is phosphoric acid, only small quantities of phosphorous acid being formed. After correction for the latter. Long and Sackman obtained AH° = —763.2+1.1 kcal/mole... 

The heat of combustion by static bomb calorimetry has been measured by Bedford and Mortimer (6), and also by Birr (12), who obtained = — 2463.3 2.3 kcal/mole and — 2461.3 3.6 kcal/mole, respectively. Bedford and Mortimer measured the amount of CO2 produced on combustion, and corrected for incomplete combustion. Accepting their result as the more reliable, the derived heat of formation is... 

Long and Sackman 106) investigated the combustion of Mc3As by static bomb calorimetry, and reported that the combustion products are a complex... 

Birr 12) measured the heat of combustion by static bomb calorimetry his results give AH°= -2392.5 2.5 kcal/mole (formation of Sb204), leading to... 

Combustion or bomb calorimetry is used primary to derive enthalpy of fonuation values and measurements are usually made at 298.15 K. Bomb calorimeters can be subdivided into tluee types (1) static, where the bomb or entire calorimeter (together with the bomb) remains motionless during the experiment (2) rotating-... 

IMR = ion-molecule reactions RB = rotating-bomb combustion calorimetry RC = reaction calorimetry SB = static-bomb combustion calorimetry. 

There is general agreement that static-bomb combustion calorimetry is inherently unsatisfactory to determine enthalpies of formation of organolead compounds2,3. Unfortunately, as shown in Table 6 only three substances have been studied by the rotating-bomb method. The experimentally measured enthalpies of formation of the remaining compounds in Table 6 were determined by reaction-solution calorimetry and all rely on AH/(PbPh4, c). 

Static-bomb combustion calorimetry is particularly suited to obtaining enthalpies of combustion and formation of solid and liquid compounds containing only the elements C, H, O, and N. The origins of the method can be traced back to the work of Berthelot in the late nineteenth century [18,19]. 

Flame combustion calorimetry in oxygen is used to measure the enthalpies of combustion of gases and volatile liquids at constant pressure [54,90]. Some highly volatile liquids (e.g., n-pentane [91]) have also been successfully studied by static-bomb combustion calorimetry. In general, however, the latter technique is much more difficult to apply to these substances than flame combustion calorimetry. In bomb combustion calorimetry, the sample is burned in the liquid state and must be enclosed in a container prior to combustion. Encapsulation may be difficult, because it is necessary to minimize the amount of vaporized compound inside the container as much as possible. In addition, volatile liquids tend to burn violently under a pressure of 3.04 MPa of oxygen, which leads to incomplete combustion. These problems are avoided in flame combustion calorimetry, where the sample is carried to the combustion zone as a vapor and burned under controlled conditions at atmospheric pressure. 

Accurate experimental enthalpies of formation of iV-suhstituted imidazoles were measured using static bomb combustion calorimetry, the vacuum suhlimation drop method, and the Knudsen-effusion method <1999PCA9336>. 

The so-derived enthalpy of formation of gaseous triphenylarsine oxide, 261 18 kcalmol , just overlaps the value obtained from rotating bomb calorimetry, 227.6 +15.6 kJ mol . While related success arises in the comparison of the values for triphenylphosphine oxide we admit our discomfort with the large error bars accompanying all of these values. As such, while we derive an enthalpy of formation of triphenylstibine oxide using the static bomb results for stibine—and thus enter this value into Table 1—we regrettably consider it pointless even to compare the E—O bond enthalpies for the three triphenyl compounds. 

To the best of our knowledge, PhC=CAg is the only other silver acetylide for which there is a measured enthalpy of formation. Indeed, it is the only other classical silver organometalhc compound for which the standard enthalpy of formation has become available in this century Using static-bomb combustion calorimetry, Bykova and her coworkers11 determined this value to be 346.3 2.0 kJ mol-1. 

Bostic et al. (113) reported on a series of PCT fabrics treated with selected phosphorus- and halogen-containing flame retardants which were studied by static oxygen bomb calorimetry. The amount of heat evolved when these fabrics were burned in the open atmosphere was determined indirectly using calculations based on Hess law of summation. The heat evolution, when corrected for contributions due to burning of the flame retardant, appeared to correlate with the efficiency of the flame retardant treatment and was interpretable in terms of mechanisms of flame retardant action. 

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