Calorimetric determinations

Randzio S L 1994 Calorimetric determination of pressure effects Solution Calorimetry, Experimental Thermodynamics vol IV, ed K N Marsh and PAG O Hare (Oxford Blackwell)... 

D. L. OmeUos, Calorimetric Determination of the Heats and Products of Detonation for Explosives, Lawrence Livermore Lab. (LLL), Livermore, Calif., Apr. 1982. 

See also under Calorimeter, Calorimetry and Calorimetric Determinations in Vol 2, C10-L to C12-R... 

Use of thermal stability tests (DTA s) to determine the heat sensitivity of a given process mixture is desirable. Recent advances in analytical methods permit good calorimetric determination of heat of reaction. Heat of reaction data are critical for exothermic reactor vent sizing. Heat impact from fire is usually small in comparison, but should not be neglected. 

Attree RW, Cabell MJ, Cushing RL, Pieroni JJ (1962) A calorimetric determination of the half-life of thorium-230 and a consequent revision to its neutron capture cross section. Can J Phys 40 194-201 Bateman H (1910) Solution of a system of differential equations occurring in the theory of radioactive transformations. Proc Cambridge Phil Soc 15 423-427 Beattie PD (1993) The generation of uranium series disequilibria by partial melting of spinel peridotite ... 

Two general procedures have been used to obtain AH values. The first involves the measurement of log K values over a range of temperatures the observed variation may be used to derive the required AH value. However, because of the usual errors inherent in log K determinations coupled with the limited temperature range normally possible, AH values obtained in this manner tend to be somewhat unreliable. In contrast, the direct determination of AH using calorimetry commonly results in values which are considerably more accurate. Nevertheless, such calorimetric determinations may still not be easy for particular macrocyclic systems. Difficulties can arise in measuring the total heat evolved for metal complexation when long equilibration times are necessary. To lessen such problems, sensitive calorimeters have been used which are able to integrate the heat released over an extended time. 

Sandell EB (1959) Calorimetric determination of traces of metals. Interscience, New York... 

There seem to be no direct calorimetric determinations of enthalpies of solution of rare-earth tribromides in nonaqueous solvents,3 and very few reports on the temperature variation of solubilities whence solution enthalpies might be roughly estimated. The most detailed set of data concerns cerium tribromide in pyridine (257). In this system there exists a series of solvates (cf. Section IH,C,2), but sufficient solubilities were determined for the estimation of enthalpies of solution of each solvate. These enthalpies are included in Fig. 3, which shows an extraordinary zig-zag variation of solubility with temperature. The actual values of enthalpies of solution cannot be accurate, but at least it is clear that they change sign and magnitude in an eccentric manner. 

I. Tomaszkiewicz, G. A. Hope, C. M. Beck II, P. A. G. O Hare. Thermodynamic Properties of Silicides. VI. Pentamolybdenum Trisilicide (Mo Sf). Fluorine Combustion Calorimetric Determination of the Standard Molar Enthalpy of Formation at the Temperature of 298.15 K. J. Chem. Thermodynamics 1997, 29, 87-98. 

Calorimetric Determination of Enthalpies of Binary and Multicomponent Mixtures of Components Encountered in SNG Processes"... 

Ulbrich and Waldbaum [14] pointed out that calorimetrically determined third law entropies for many geologically important minerals may be in error because site mixing among cations, magnetic spin disorder, and disorder among water molecules in the crystals is frozen in the samples used for calorimetric measurements. They have calculated corrections based on known crystallographic data for several minerals. 

In deahng with solutions, it frequently may be necessary to obtain values of AG for a process in solution for which only thermal data are available. If standard entropy data also could be obtained for solutions, then it would be possible to calculate AG° from a calorimetric determination of AH° and from Equation (7.26) ... 

Hill, J.O., Worsley, EG., and L.G. Hepler. Calorimetric determination of the distribution coefficient and thermodynamic properties of bromine in water and carbon tetrachloride, J. Phys. Chem., 72(10) 3695-3697, 1968. 

The report of Gmndnes and Christian (14) presents another interesting complication from solvent effects. The reported enthalpy of formation of the (CHg)3N—SOg adduct in the gas phase is — 9.1 0.4 k. cal mole i, while that measured in heptane is — 11.03 0.3. The cause of this discrepancy is not understood and before drawing any definite conclusions about the nature of the solvent effects in this system, it would be informative to have a calorimetrically determined enthalpy in... 

We have found a direct calorimetric determination of both K and AH° to be capable of producing much more reliable thermodynamic data than infrared or ultraviolet-visible spectroscopy. Furthermore, things that react extensively have enthalpies but may not have convenient changes in absorption bands. The procedure for the simultaneous determination of K and AH° from calorimetric measurements has been described (20—22). 

Handa, Y.P. (1986b). Calorimetric determinations of the compositions, enthalpies of dissociation, and heat capacities in the range 85 to 270 K for clathrate hydrates of xenon and krypton. J. Chem. Thermodynamics, 18 (9), 891-902. 

In this section a method for the direct calorimetric determination of heats of adsorption on evaporated metal films is described and results for the heals of adsorption of hydrogen on nickel, iron, and tungsten are reported. In all cases the heats of adsorption decrease with the fraction of surface covered in a mode that can satisfactorily be explained by interaction of adsorbed atoms. A criterion for mobility of the adsorbed atoms is developed... 

The idea of calorimetry is based on the chemical reaction characteristic of molecules. The calorimetry method does not allow absolute measurements, as is the case, for example, with volumetric methods. The results given by unknown compounds must be compared with the calibration curve prepared from known amounts of pure standard compounds under the same conditions. In practical laboratory work there are very different applications of this method, because there is no general rule for reporting results of calorimetric determinations. A conventional spectrophotometry is used with a calorimeter. The limitations of many calometric procedures lie in the chemical reactions upon which these procedures are based rather than upon the instruments available . This method was first adapted for quinolizidine alkaloid analysis in 1940 by Prudhomme, and subsequently used and developed by many authors. In particular, a calorimetric microdetermination of lupine and sparteine was developed in 1957. The micromethod depends upon the reaction between the alkaloid bases and methyl range in chloroform. 

Heats of adsorption are usually determined in two ways either by direct calorimetric determination at a chosen temperature, or by calculating the isosteric heats from adsorption isotherms measured at different temperatures and using the Clausius-Clapeyron equation. Thus, isosteric heats of adsorption are calculated from the... 

In the direct calorimetric determination (-AH = f(njj), the amount adsorbed (nj is calculated either from the variations of the gas pressure in a known volume (volumetric determination) or from variations of the weight of the catalyst sample in a static or continuous-flow apparatus (gravimetric determination), or from variations of the intensity of a mass spectrometer signal [151]. 

Fig. 2. Calorimetrically determined molar heats of adorption of ammonia at 623 K on H7 25K2.25-L.

Fig. 5. Comparison of calorimetrically determined heats of adsorption (circles) with the energy level histogram for H7,26K2.25-L.

Kugimiya, M., Donovan, J. W. (1981). Calorimetric determination of the amylose-lysolecithin complex. Journal of Food Science, 46, 765. 

The wide range of results obtained in the apparently straightforward calorimetric determinations of TNT [heat of explosion 689.3 cal/g, gaseous products 960.3 cc/g (Picatinny Arsenal Physico-Chemical Unit Report No 52-HI-595, 4 Mar, 1952) as against heat of explosion 1080 cal/g, gaseous products 730 cc/g [Picatinny Arsenal Technical Report (PATR) 1740, Rev 1(1958), p 31911 suggests the occurrence of two different chemical reactions, possible similar to the following in the two respective cases ... 

Start test at RT and program to 250°C. Ignition temp is interpreted to be the point at which the exothermic degradation begins, point A of Fig Et 19. Peak degradation temp is indicated by point B Note Description of "Calorimeter, Calorimetry Calorimetric Determinations is given in Vol 2 of... 

There is one other report in the literature of a measurement of the enthalpy of formation of an organomagnesium halide. The enthalpy of reaction of magnesium with methyl iodide in ether was calorimetrically determined as —273.6 0.8 kJmoH Using a recent enthalpy of formation for liquid methyl iodide of —13.6 0.5 kJmoU, the enthalpy of formation of methylmagnesium iodide is —287.2 kJmoU. The exchange (equation 8) is thus 11.2 kJmoU endothermic. 

There is a report of calorimetrically-determined enthalpies of reaction of methyl- and ethyhnagnesium bromides with some ketones in ether solution at 15 °C. The reaction shown in equation 13, which results in an exotherm of —202.3 kJmoU, produces an alkoxymagnesium bromide that also appears as a product of a different reaction in Table 4. Using the enthalpy of formation of MeMgBr and the liquid phase enthalpy of formation of acetone, the enthalpy of formation of the f-butoxymagnesium bromide is calculated as —783.5 kJmol . This is within 10 kJmoU of the value reported in Table 4. 

In comparison, too, direct calorimetric determination of heats of adsorption can be less accurate, although less tedious, than heat-of-immersion determinations. Lack of accuracy can occur with poorly conducting, non-metallic adsorbents, where long equilibrium times are required for vapor phase adsorption or where surface sites do not fill in strict accordance with the site energy distribution of the solid surface. Atoms or molecules can be expected to stick to the first part of the surface they strike when strong chemisorption occurs and then molecules are likely not to move freely over... 

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