Liquid phase calorimetry

Calorimetric techniques, and liquid phase calorimetry in particular, are promising methods to study catalytic reactions [39]. Notably, the use of a differential reaction calorimeter (DRC) makes it possible to determine the most important thermodynamic data such as the heat of reaction and heat capacity of the system [40-42]. 

The study of Garron et al. [43] is one of the first investigations by liquid-phase calorimetry of the mechanism of hydrogen generation by hydrolysis of sodium... 

In solute-solvent calorimetry the compound to be studied is present as a mixture with another element or compound in solid form at room temperature and dropped into a hot calorimeter with resulting formation of a liquid product [35], In order to determine the enthalpy of formation of LaBg, Pt was added in a proportion that gave the composition of a low melting eutectic. The liquid phase formed enhanced the reaction rate and enabled the energetic parameters to be extracted [46],... 

About 30 years ago, an enthalpy of formation was reported for 3,3,4,4-tetramethyl-l,2-dioxetane . Both by direct microcalorimetric combustion measurements of the neat solid and by reaction calorimetry (of the solid itself, and in acetone solution to form acetone), a consensus value was derived. Now, is the enthalpy of formation plausible , notwithstanding the very large error bars Consider reaction 6 for the dioxetane that produces 2,3-dimethyl-2,3-butanediol . The liquid phase enthalpy of reaction is —329 kJmoU. It is remarkable that this value is compatible with that for the dialkyl peroxides, ca —335 kJmoU, despite the ring strain that might be expected. 

The enthalpies of formation of the cycloalkylmagnesium bromides that have been determined by reaction calorimetry are listed in Table 3. As with other functionalized cycloalkanes and the cycloalkanes themselves, there is no regularity to these values with respect to carbon number as there are for their acyclic analogs because of the influence of ring strain on the enthalpies. Unfortunately, there are no enthalpies of formation for the bromocycloalkanes with which to compare these values there are, however, enthalpies of formation for liquid phase cycloalkanes. Figure 3 is a plot of the enthalpies of formation for the cycloalkyl-MgBr vs. those for cycloalkyl-H. There is a linear relationship with... 

Differential Scanning Calorimetry (DSC) is a sensitive way of detecting phase transformations of a bulk material [85,86]. Monitoring the thermal behavior of a crystal or a powder as a function of its conversion to product can give important information. This technique can verify whether a reaction occurs in a purely solid phase or whether there may be liquid phases involved at a given temperature. Melting point depression can be monitored as product appears, and the characteristic melting of a new phase can be detected if one is formed. DSC can reveal whether or not a eutectic transition attributable to a mixture of phases is present. We have also used DSC in our lab to monitor the thermal stability of reactive crystals. 

Nuclear magnetic resonance (NMR) can be used as a rapid alternative to differential scanning calorimetry in the determination of the solid fat content and studies on the melting behaviour. The determination is based on detection of the different populations of protons in solid and liquid phases, which indicates the hardness of the fat. Hernandez and Rutledge (1994b) used low resolution pulse NMR to compare melting curves of roasted and non-roasted cocoa butters from Africa, Indonesia and South America. Discriminant analysis techniques showed... 

In addition to calorimetry, information to establish the mode of adsorption is often obtained spectroscopically. Changes in the optical properties of (groups on) the surface or the adsorptive may be monitored. As an Illustration of the former. Rochester studied adsorption from the gas euid liquid phase on rutile (TiOj) and used infrared spectroscopy to distinguish between attachment at different surface hydroxyls. As an example of an ESR study, McBride investigated the adsorption of fatty acids on amorphous alumina from methanol by labelling them with a spin probe. Relevant information could be... 

The heat capacity of thiazole was determined by adiabatic calorimetry from 5 to 340°K by Goursot and Westrum (295,296). A glass-type transition occurs between 145 and 175 K. Melting occurs at 239.53°K (-33.62°C) with an enthalpy increment of 2292 cal mole" and an entropy increment of 9.57 cal mole" -"K". Table 1-44 summarizes the variations as a function of temperature of the most important thermodynamic properties of thiazole molar heat capacity Cp, standard entropy S°, and Gibbs function -(G°-The variation of Cp for crystalline thiazole between 145 and 175°K reveals a marked inflection that has been attributed to a gain in molecular freedom within the crystal lattice. The heat capacity of the liquid phase varies nearly linearly with temperature to 310°K, at which temperature it rises more rapidly. This thermal behavior, which is not uncommon for nitrogen compounds, has been attributed to weak intermolecular association. The remarkable agreement of the third-law ideal-gas entropy at... 

FIGURE 13.20. Differential scanning calorimetry trace. The heating curve for 1,1,2-trichloro-2,3,3-trifluorocyclobutane. The larger peak is due to the transition from the anisotropic crystalline phase to the plastic crystalline phase the smaller peak is due to the transition from the plastic crystalline pheise to the liquid phase. (Courtesy V. B. Pett and David L. Powell, The College of Wooster, Ohio.)... 

The vibrational assignment is from force-constant calculations of Toyuki and Shimizu (1 ). Pfeiffer s assignment ( 15) is only slightly different and results in negligible change in the thermodynamic functions. Spectral data were summarized by Gillespie and Robinson ( ) in their study of the liquid-phase Raman spectra. Only those frequencies above 500 cm are based on gas-phase spectra. Trautz et al. (1 ) found Cp = 15.4 + 0.3 J K mol by calorimetry at 43 mmHg and 16 to 99 C this Cp is too low, like ( ), and the error is almost 20%. 

Treverton and Margrave (3) also used levitation calorimetry to measure the liquid phase enthalpy of molybdenum in the range... 

Reaction calorimetry provides useful insights here even if direct enthalpy of formation measurements are absent. Liquid phase isomerization of the o- to p-tcrt-butylphenol has been shown to be exothermic hy 16.9 1.6 kJ mol [T. N. Nesterova, S. P. Verevkin, T. N. Malova and V. A. Pil shchikov, Zh. Prikl. Khim., 58, 827 (1985) Chem. Abstr., 103, 159918x (1985)] while the p- to m-isomerization in both the Uquid and gas phase is exothermic by ca 1 kJ mol [cf. V. A. Pil shchikov, T. N. Nesterova and A. M. Rozhnov, J. Appl. Chem. USSR, 54, 1765... 

It is indisputable that ILs can be widely applied to functionalize CNTs due to their excellent dispersing power. Recently, liquid-phase exfoliation of CNTs has been reviewed by Coleman [61] however, the dispersion mechanism for CNTs in ILs is still controversial. A cation-jt interaction between nanotubes and imidazolium ions was first proposed by Fukushima and Aida [55,57] to account for the exfoliation of entangled SWCNTs into smaller bundles, even individuals. On the basis of combined results of differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectrum, and X-ray diffraction (XRD) analysis, Gilman et al. [81] provided the evidence for a cation-Ti interaction in the imidazolium-treated MWCNTs. Some researchers also cited this interpretation to support their cases [82]. 

Bonell [72BON] used levitation calorimetry to measure the heat content of liquid zirconium in the temperature range 2233 to 3048 K, referring to a reference temperature of 2128 K (the melting point of zirconium see Section V. 1.1.1). The data obtained were linear with respect to temperature (Figure V-6) indicating that the heat capacity of the liquid phase is a constant. The value of the heat capacity determined for liquid zirconium from the data of [72BON] is ... 

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