Calorimetry principle

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. 

Most reaction calorimeters work according to heat-flow calorimetry principles. The heat of reaction evolved from a reaction mixture running at under isothermal conditions is transferred to the fluid in the cooling jacket according to the equation... 

Brown, M.E., Ed., Differential thermal analysis and differential scanning calorimetry, in Handbook of Thermal Analysis and Calorimetry Principles and Practice, Vol. 1, Haines, P.J., Reading, M., and Wilburn, F.W., Elsevier, Amsterdam, 1998, chap. 5. 

M. E. Brown, ed.. Handbook of Thermal Analysis Calorimetry Principles and Practice, Elsevier, Amsterdam, 1999. 

Mullens J. (1998), Evolved gas analysis, In Handbook of Thermal Analysis and Calorimetry Principles and Practice, Elsevier Science, pp. 509-546. 

Calorimetry is the basic experimental method employed in thennochemistry and thennal physics which enables the measurement of the difference in the energy U or enthalpy //of a system as a result of some process being done on the system. The instrument that is used to measure this energy or enthalpy difference (At/ or AH) is called a calorimeter. In the first section the relationships between the thennodynamic fiinctions and calorunetry are established. The second section gives a general classification of calorimeters in tenns of the principle of operation. The third section describes selected calorimeters used to measure thennodynamic properties such as heat capacity, enthalpies of phase change, reaction, solution and adsorption. 

The basic principle of heat-flow calorimetry is certainly to be found in the linear equations of Onsager which relate the temperature or potential gradients across the thermoelements to the resulting flux of heat or electricity (16). Experimental verifications have been made (89-41) and they have shown that the Calvet microcalorimeter, for instance, behaves, within 0.2%, as a linear system at 25°C (41)-A. heat-flow calorimeter may be therefore considered as a transducer which produces the linear transformation of any function of time f(t), the input, i.e., the thermal phenomenon under investigation]] into another function of time ig(t), the response, i.e., the thermogram]. The problem is evidently to define the corresponding linear operator. 

In this chapter, we describe how time-resolved photoacoustic calorimetry (PAC) can be used to obtain both the energetics and kinetics of carbenes in solution.7-9 PAC measures the magnitude and temporal profile of volume changes in solution following deposition of energy. These time-resolved volume changes can be directly related to carbene reaction enthalpies. We will first discuss the principles of this photoacoustic technique and then how it has been... 

Differential scanning calorimetry (DSC) is a technique which aims to study the same thermal phenomena as DTA, but does so on a rather different principle. Hence, although the data obtained are very similar, they may differ in detail. Typical DSC equipment will operate over the temperature range from ambient to ca. 700°C. However, as with DTA, specially modified equipment can extend this substantially in both directions. 

Heat capacities at high temperatures, T > 1000 K, are most accurately determined by drop calorimetry [23, 24], Here a sample is heated to a known temperature and is then dropped into a receiving calorimeter, which is usually operated around room temperature. The calorimeter measures the heat evolved in cooling the sample to the calorimeter temperature. The main sources of error relate to temperature measurement and the attainment of equilibrium in the furnace, to evaluation of heat losses during drop, to the measurements of the heat release in the calorimeter, and to the reproducibility of the initial and final states of the sample. This type of calorimeter is in principle unsurpassed for enthalpy increment determinations of substances with negligible intrinsic or extrinsic defect concentrations... 

The basic principle of solution calorimetry is simple. In one experiment the enthalpy of solution of, for example, LaA103(s) [32] is measured in a particular solvent. In order to convert this enthalpy of solution to an enthalpy of formation, a thermodynamic cycle, which gives the formation reaction... 

Conventional combustion calorimeters operate on a macro scale, that is, they require samples of 0.5-1.0 g per experiment. Unfortunately, many interesting compounds are available only in much smaller amounts. In the case of oxygen combustion calorimetry, however, several combustion microcalori-meters that only demand 2-50 mg samples have been developed in recent years. The achievements and trends in this area through 1999 have been reviewed [7-10], and interested readers are directed to these publications. Since then, a few new apparatus have been reported [11-17], Nevertheless, it should be pointed out that the general principles and techniques used to study compounds at the micro scale are not greatly different from those used in macro combustion calorimetry. 

The principles of titration calorimetry will now be introduced using isoperibol continuous titration calorimetry as an example. These principles, with slight modifications, can be adapted to the incremental method and to techniques based on other types of calorimeters, such as heat flow isothermal titration calorimetry. This method, which has gained increasing importance, is covered in section 11.2. 

As mentioned above, titration methods have also been adapted to calorimeters whose working principle relies on the detection of a heat flow to or from the calorimetric vessel, as a result of the phenomenon under study [195-196,206], Heat flow calorimetry was discussed in chapter 9, where two general modes of operation were presented. In some instruments, the heat flow rate between the calorimetric vessel and a heat sink is measured by use of thermopiles. Others, such as the calorimeter in figure 11.1, are based on a power compensation mechanism that enables operation under isothermal conditions. 

S. Sunner. Basic Principles of Combustion Calorimetry. In Experimental Chemical Thermodynamics, vol. 1 Combustion Calorimetry S. Sunner, M. Mansson, Eds. IUPAC-Pergamon Press Oxford, 1979 chapter 2. 

P. J. Haines, M. Reading, F. W. Wilburn. Differential Thermal Analysis and Differential Scanning Calorimetry. InHandbookofThermal Analysis and Calorimetry, vol 1 Principles and Practice M. E. Brown, Ed. Elsevier Amsterdam, 1998 chapter 5. 

Isotopic methods Indirect calorimetry is limited by the need to measure the gases, which means that it cannot be used for free-living studies. Consequently, methods involving the administration of isotopically labelled compounds have been devised. These are based on the principle of isotopic dilution, a widely employed method for estimating concentrations, particularly of hormones and other proteins in the blood (Appendix 2.6). The requirements for these methods are ... 

However, the determination of affinity does not necessarily have to rely on labeled ligands. It is also possible with native ligands when using suitable detection methods, as for example nuclear magnetic resonance (NMR), surface plasmon resonance (SPR), acoustic biosensors or calorimetry [48, 49]. A particularly versatile and sensitive detection principle for the investigation of interactions between targets and native ligands is mass spectrometry [50]. 

With a somewhat stiffer monomer, 1,6-hexanediol diacrylate, (HDDA) we have previously observed that the ultimate conversion as measured with differential scanning calorimetry (DSC) also depends on light intensity. This has been attributed to the experimentally observed delay of shrinkage with respect to chemical conversion (7). In principle, such a dependence of conversion on intensity should show up in the mechanical properties as well. However, these are difficult to measure with thin samples of HDDA. 

Another method to obtain enthalpies of formation of compounds is by solute-solvent drop calorimetry. This method was pioneered by Tickner and Bever (1952) where the heat formation of a compound could be measured by dissolving it in liquid Sn. The principle of the method is as follows. If the heat evolved in the dissolution of compound AB is measured, and the equivalent heat evolved in the dissolution of the equivalent amount of pure A and B is known or measured, the difference provides the enthalpy of formation of the compound AB. Kleppa (1962) used this method for determining enthalpies of formation of a number of Cu-, Ag- and Au-based binaries and further extended the use of the method to high-melting-point materials with a more generalised method. 

An apparatus with high sensitivity is the heat-flow microcalorimeter originally developed by Calvet and Prat [139] based on the design of Tian [140]. Several Tian-Calvet type microcalorimeters have been designed [141-144]. In the Calvet microcalorimeter, heat flow is measured between the system and the heat block itself. The principles and theory of heat-flow microcalorimetry, the analysis of calorimetric data, as well as the merits and limitations of the various applications of adsorption calorimetry to the study of heterogeneous catalysis have been discussed in several reviews [61,118,134,135,141,145]. The Tian-Calvet type calorimeters are preferred because they have been shown to be reliable, can be used with a wide variety of solids, can follow both slow and fast processes, and can be operated over a reasonably broad temperature range [118,135]. The apparatus is composed by an experimental vessel, where the system is located, which is contained into a calorimetric block (Figure 13.3 [146]). 

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