Calorimetry bomb

With most non-isothemial calorimeters, it is necessary to relate the temperature rise to the quantity of energy released in the process by determining the calorimeter constant, which is the amount of energy required to increase the temperature of the calorimeter by one degree. This value can be detemiined by electrical calibration using a resistance heater or by measurements on well-defined reference materials [1], For example, in bomb calorimetry, the calorimeter constant is often detemiined from the temperature rise that occurs when a known mass of a highly pure standard sample of, for example, benzoic acid is burnt in oxygen. 

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-... 

In recent years, fluorine bomb calorimetry has been used effectively. A number of substances that will not burn in oxygen will burn in fluorine gas. The heat resulting from this fluorine reaction can be used to calculate AfH°m. For example, Murray and 0 Hare have reacted GeS2 with fluorine and measured ArH°. The reaction is... 

A number of compounds react with F2(g) in this manner, and fluorine bomb calorimetry can be used to measure their A //°r... 

Bomb calorimetry Use of oxygen and an inert gas enables the heat of combustion and the heat of decomposition to be evaluated respectively. 

The parent 1,2,4-triazole has been investigated as a potential reference compound for use in combustion experiments of compounds that contain nitrogen atoms using a micro-bomb calorimetry experiment. Urea was used previously as a standard but the chemical and physical stability of 1,2,4-triazole lends itself to such a role <2000MI949>. 

The desired enthalpy of formation of fulvene and of its 6-methyl derivative were determined by Roth by measurement of the appropriate enthalpy of hydrogenation. The facile polymerization of this compound precludes conventional bomb calorimetry. 

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). 

The heat of formation of solid GeF2 has very recently been determined by fluorine bomb calorimetry 105 The value of AHp(GeF2, c, 298.15 °K) = -157.3 ... 

Although most of the fluorine calorimetry has been done with the elements, it has been used to burn oxides, carbides, nitrides, and chal-cogenides and hence determine their heats of formation. In some instances it has proved superior to oxygen bomb calorimetry. Thus the oxidation of boron tends to be incomplete because of oxide coating, whereas fluorination produces gaseous boron trifluoride without surface inhibition. A summary of modem fluorine calorimetry results is assembled in Table III. 

Equilibrium constants involving each compound were evaluated using the partial pressures by the third law method. Accepting the heats of formation of WF5 and WF obtained from bomb calorimetry, the values for WF (n = 1 to 4) could be extracted by iterative fitting to partial pressure data. The W/02/F2 and W/S/F2 systems were also examined to give heats of formation of tungsten oxo- and thiofluorides. This experimentally simple technique yields thermodynamic data on high-temperature species inaccessible to conventional calorimetry. 

In flame calorimetry, it is not easy to measure directly with good accuracy the mass of reactants consumed in the combustion. Therefore, the results are always based on the quantitative analysis of the products and the stoichiometry of the combustion process. In the case of reaction 7.73, the H20 produced was determined from the increase in mass of absorption tubes such as M, containing anhydrous magnesium perchlorate and phosphorus pentoxide [54,99], When organic compounds are studied by flame combustion calorimetry, the mass of C02 formed is also determined. As in bomb calorimetry, this is done by using absorption tubes containing Ascarite [54,90]. 

There have been far more thermochemical experiments carried out in fluorine than in any other halogen atmosphere, the large majority of them by fluorine bomb calorimetry [110-116]. Thus, only fluorine combustion calorimetry will be covered in this section with a strong emphasis on bomb calorimetry. Note, however, that many technical details and safety precautions mentioned here for fluorine combustion calorimetry also apply to combustion in other halogens. 

The first reported attempt to use fluorine in calorimetric measurements is probably Berthelot and Moissan s study of the reaction between K.2SC>3(aq) and F2(g), in 1891 [ 19,120]. Modem fluorine bomb calorimetry, however, was started in the 1960s by Hubbard and co-workers [110,111,121], while in the same period Jessup and Armstrong and their colleagues [ 109,115-117] developed the method of fluorine flame calorimetry to a high degree of accuracy and precision. 

Fluorine bomb calorimetry is in many aspects similar to oxygen bomb calorimetry. The experiments are carried out in isoperibol instruments, which, except for the bomb, are basically identical to those described in sections 7.1 and 7.2. The procedure used to calculate Acf/°(298.15 K) from the experimental results is also analogous to that discussed for oxygen bomb calorimetry in section 7.1. Thus, a temperature-time curve, such as the one in figure 7.2, is first acquired, and the corresponding adiabatic temperature rise, A Tad, is derived. 

Much of the discussion of oxygen flame calorimetry presented in section 7.3 is directly applicable to fluorine flame calorimetry. As in the case of bomb calorimetry, however, the special properties of fluorine combustion systems and problems associated with handling fluorine require a somewhat different experimental method [109,115,116]. Thus, for example, a metal burner should be used. Also, the fact that the mixing of many gases with F2 may lead to spontaneous ignition hinders the use of a premixed flame. Fluorine combustion calorimetry has been used to study the thermochemistry of important reactions, such as... 

S. N. Hajiev. Bomb Calorimetry. In Thermochemistry and Equilibria of Organic Compounds, book 1 M. Frenkel, Ed. VCH Publishers New York, 1993 chapter 6. 

W. D. Good, D. M. Fairbrother, G. Waddington. Manganese Carbonyl Heat of Formation by Rotating-Bomb Calorimetry. J. Phys. Chem. 1958, 62, 853-856. 

M. E. Minas da Piedade, L. Shaofeng, G. Pilcher. Enthalpy of Formation of Dycyclopentadienyltungsten Dichloride by Rotating-Bomb Calorimetry. 1 Chem. Thermodynamics 1987,19, 195-199. 

P. A. G. O Hare. The Nuts and Bolts and Results of Fluorine Bomb Calorimetry. In Energetics of Stable Molecules and Reactive Intermediates M. E. Minas da Piedade, Ed. NATO ASI Series C, Kluwer Dordrecht, 1999 55-75. 

E. Greenberg, W. N. Hubbard. Fluorine Bomb Calorimetry. XXIII. The Enthalpy of Formation of Carbon Tetrafluoride. J. Phys. Chem. 1968, 72, 222-227. 

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