Rotating-bomb calorimeter

For substances containing elements additional to C, H, O and N a rotating bomb calorimeter is generally used. A typical rotating bomb calorimeter system is shown in figure B 1.27.4. With tiiis calorimeter considerably more water is added to the combustion bomb and the continuous rotation of the bomb both about the cylindrical axis and end over... 

Figure Bl.27.4. Rotating bomb isoperibole calorimeter. A, stainless steel bomb, platinum lined B, heater C, thermostat can D, thennostat iimer wall E, themiostat water G, sleeve for temperature sensor H, motor for bomb rotation J, motor for calorimeter stirrer K, coimection to cooling or heating unit for thennostat L, circulation pump.

Figure 7.7 Scheme of an isoperibol macro rotating-bomb combustion calorimeter. A calorimeter proper B bomb C thermostatic bath D motors for rotation of the bomb E drive shaft F stirrer of the calorimeter proper G motor that drives the stirrer F H motor that drives the stirrer of the thermostatic bath I miter gear J gas outlet valve K gas inlet valve L crucible. 

Figure 7.8 Scheme of a micro rotating-bomb aneroid combustion calorimeter [75,76]. 

Other calorimeters include heat-leak calorimeters", such as of Thomas Parks (Ref 25,p 545), "automatic calorimeters such as of Andrews, Berl Stull (Ref 25,p 551) "vacum-walled calorimeter (Ref 3,p 153) "aneriod (unstirred) calorimeters" (Ref 3,pp 23,160-7), "rotating bomb calorimeters", such as of Popov, Shirokikh and of Hubbard (Ref 25,p 594) liquid-phase calorimeter" of Kistiakowsky (Ref 25,p 636), "gas calorimeter of Cutler- Hammer (Ref 18a), calorimeter for gaseous heat capacities of Waddington (Ref 15,p 802), "flow calorimeter of Junkers (Ref 15,p 805)," flow calorimeter of Osborne et al (Ref 25,p 565), "flow calorimeter of Pitzer (Ref 25,p 566), "flow calorimeter of Bennewitz Schulze (Ref 25,p 567) and "fiame calorimeter of Rossini" (Ref 25,pp 600--2). An apparatus for detn of heats of vaporization is described in Ref 25,p 615 and an "adsorption calorimeter in Ref 25,p 618... 

Chemists always need to know bond energies, often for unusual combinations of elements, for which bomb combustion calorimetry experiments have never been done, partly because the appetite of conventional bomb combustion calorimeters for large samples is not easily met for rare compounds. Thus there is a need for future micro rotating-bomb calorimeters. 

We begin with fluorophenols. Disappointingly, the data are old , and because the calorimeter was not a rotating bomb and the products were not analyzed, the results are not particularly to be trusted . In any case, the enthalpies of formation are only for the condensed phase. That the enthalpy of fusion is always endothermic means the enthalpy of formation of a liquid must be less negative than the corresponding solid. 

The enthalpy of formation of Se02(cr) is obtained from the three accepted measurements of the heat of combustion of Se(trigonal) listed in Table V-22 (references to earlier experimental results or selected values in compilations can be found in [62GAT]). Selenium reacts only partly with oxygen in the bomb calorimeter unless mixed with a combustion aid. Benzoic acid was used for this purpose and the heat evolved by the combustion aid was about 50% in the static bomb and about 90% in the rotating bomb experiments. 

Because high-precision combustion calorimeters equipped with rotating macrobombs are not commercially available, a new rotating-bomb combustion calorimeter has recently been re-designed [187] and has yielded good results in combustion experiments with the reference compound thianthrene. 

Mortimer and Sellers 123) used a rotating-bomb calorimeter to measure the heat of reaction of Me3Al with acetic acid, in toluene solution... 

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-... 

The energy produced in the calorimeter proper as a result of friction in the rotating mechanism and stirring of the calorimetric liquid by the rotation of the bomb may be substantial. Yet provided that this effect is constant, its contribution to the energy of the calorimetric process can be accurately subtracted. If the bomb is rotated during the calibration and the sample runs, and if the rotation is started and ended at the same instants of the respective main periods, then the energy... 

The corrections due to the bomb rotation can also be eliminated by using a dynamic calorimeter, in which the whole calorimeter is rotated and the rotation mechanism is outside the calorimeter proper. An example of such instrument is the aneroid calorimeter developed by Adams, Carson, and Laye [77], shown in figure 7.9. 

Figure 7.9 Scheme of the aneroid dynamic combustion calorimeter designed by Adams, Carson, and Laye [77], A jacket B jacket lid C motor that drives the rotation of calorimetric system D rotation system E bomb (which is also the calorimeter proper) F channels to accommodate the temperature sensor, which is a copper wire resistance wound around the bomb G crucible H electrode I gas valve. Adapted from [77]. 

Sunner doubts whether the technique of Huffman and Ellis 4 of putting no water in the bomb originally is sufficient to ensure a uniform concentration of sulphuric acid in the products, and prefers to use a moving bomb calorimeter in which the bomb is rotated so that the liquid initially placed in the bomb washes the whole internal surface of the bomb after the ignition. This certainly achieves the object of a uniform concentration, but leads to considerable mechanical difficulties. These difficulties have been surmounted and a test of the accuracy of the moving bomb calorimeter using paraffin oil has shown that it is possible to reproduce values of heats of combustion in two different calorimeters to within 0 01 per cent. This accuracy is comparable with the best attainable in stationary calorimeters Sunner 6 compared his results for cystin and cystein with those of Huffman and Ellis 234 d found those of the latter to be 0 4 per cent low. It is not certain whether the difference between the two sets of results is due to the differences in calorimetric technique or to differences in purity of the samples. 

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