Bomb combustion calorimetry

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). 

The energy change associated with the process under study induces an energy change of the calorimeter proper, which can be determined by monitoring a corresponding temperature change or heat flux. In some calorimeters the reaction occurs in a closed vessel whose volume does not vary in the course of the experiment. This happens, for example, in bomb combustion calorimetry, where the reaction takes place inside a pressure vessel called the bomb, and in... 

As referred to in the previous chapter, in bomb combustion calorimetry the reaction proceeds inside a pressure vessel—the bomb—at constant volume, and in this case the derived quantity is Ac U°. In flame calorimetry the reaction occurs in a combustion chamber, which is in communication with the atmosphere, and the measurements lead to ACH°. The methods of combustion calorimetry will be described in the following paragraphs. 

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. 

The experimental data and the calculations involved in the determination of a reaction enthalpy by isoperibol flame combustion calorimetry are in many aspects similar to those described for bomb combustion calorimetry (see section 7.1) It is necessary to obtain the adiabatic temperature rise, A Tad, from a temperaturetime curve such as that in figure 7.2, to determine the energy equivalent of the calorimeter in an separate experiment and to compute the enthalpy of the isothermal calorimetric process, AI/icp, by an analogous scheme to that used in the case of equations 7.17-7.19 and A /ibp. The corrections to the standard state are, however, much less important because the pressure inside the burner vessel is very close to 0.1 MPa. 

M. Mansson. Miniaturization of Bomb Combustion Calorimetry. In Experimental Chemical Thermodynamics, vol. 1 Combustion Calorimetry-, S. Sirnner, M. Mansson, Eds. IUPAC-Pergamon Press Oxford, 1979 chapter 17. 

M. E. Minas da Piedade. Oxygen Bomb Combustion Calorimetry Principles and Applications to Organic and Organometallic Compounds. In Energetics of Stable Molecules and Reactive Intermediates, M. E. Minas da Piedade, Ed. NATO ASI Series C, Kluwer Dordrecht, 1999. 

R. C. Santos, H. P. Diogo, M. E. Minas daPiedade. The Determination of the Standard Molar Enthalpy of Formation of 4-Chlorobenzoic Acid by Micro Rotating-Bomb Combustion Calorimetry.J. Chem. Thermodynamics 1999, 31, 1417-1427. 

A. T. Hu, G. C. Sinke, M. Mansson, B. Ringner. Test Substancesfor Bomb Combustion Calorimetry. p-Chlorobenzoic Acid. J. Chem. Thermodynamics 1972, 4, 283-299. 

Bomb" combustion calorimetry or constant-volume calorimetry is a technique that dates back to Lavoisier178 (Fig. 11.76), is now mostly relegated to undergraduate teaching laboratories and is in bad need of a renaissance. It measures the internal energy of combustion AEc, which is easily converted to AHc, and then converted to standard enthalpies of formation AHf s.is- In a typical "macro" experiment, with commercially available equipment, a very carefully measured mass m (-2.0 g) of a sample of molar mass M g/mol and... 

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. 

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>. 

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. 

These authors measured the enthalpies of combustion of thorium and plutonium carbides by oxygen bomb combustion calorimetry. 

For comparison, a value measured by static bomb combustion calorimetry has been reported as 33.1 kJ/mol, a difference of 6.0%. 

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