Calorimetric measure

The error attributed to the determination of the NHV (calorimetric measurement, determination of hydrogen content, and final calculation) is satisfactory with a repeatability of 0.3% and a reproducibility of 0.4%. 

There are numerous references in the literature to irreversible adsorption from solution. Irreversible adsorption is defined as the lack of desotption from an adsoibed layer equilibrated with pure solvent. Often there is no evidence of strong surface-adsorbate bond formation, either in terms of the chemistry of the system or from direct calorimetric measurements of the heat of adsorption. It is also typical that if a better solvent is used, or a strongly competitive adsorbate, then desorption is rapid and complete. Adsorption irreversibility occurs quite frequently in polymers [4] and proteins [121-123] but has also been observed in small molecules and surfactants [124-128]. Each of these cases has a different explanation and discussion. 

Other properties of association colloids that have been studied include calorimetric measurements of the heat of micelle formation (about 6 kcal/mol for a nonionic species, see Ref. 188) and the effect of high pressure (which decreases the aggregation number [189], but may raise the CMC [190]). Fast relaxation methods (rapid flow mixing, pressure-jump, temperature-jump) tend to reveal two relaxation times t and f2, the interpretation of which has been subject to much disagreement—see Ref. 191. A fast process of fi - 1 msec may represent the rate of addition to or dissociation from a micelle of individual monomer units, and a slow process of ti < 100 msec may represent the rate of total dissociation of a micelle (192 see also Refs. 193-195). 

As seen in previous sections, the standard entropy AS of a chemical reaction can be detemiined from the equilibrium constant K and its temperature derivative, or equivalently from the temperature derivative of the standard emf of a reversible electrochemical cell. As in the previous case, calorimetric measurements on the separate reactants and products, plus the usual extrapolation, will... 

Hansen L D, Eatough D J, Lewis E A and Bergstrom R G 1990 Calorimetric measurements on materials undergoing autocatalytic decomposition Can. J. Chem. 68 2111-14... 

The calorimetrically measured AH is usually assigned to the fonnation and breaking of chemical bonds. The equation... 

An independent measurement of the energy difference between secondary and tertiary cations in solution is available from calorimetric measurement of the enthalpy... 

Eventually one can also estimate the change in specific heat when correlations are accounted for. Specific heat offers a possibility of experimental calorimetric measurement of the typical scission energy J. Eq. (13), along with (16), yields Cy oc S/ct)° )[J/ k-QT)f Qxp[-S/ k-QT)]. Thus Cy attains its maximum now at /max/( B ) = 2/ which shifts slightly to higher values at lower densities (from 4 above / to 4.4 below). 

Similar measurements were made for the heat of precipitation of silver iodide,5 which is even less soluble in water than silver chloride. As shown in Table 33 in Sec. 102, a saturated solution of Agl at 25°C contains only 9.08 X 10-9 molcs/liter, as compared with 1.34 X 10-6 for AgCl. By calorimetric measurement the heat of precipitation of Agl at 25°C was found to be 1.16 electron-volts per ion pair, or 20,710 cal/mole. 

Since the saturated solutions of AgT and AgCl are both very dilute, it is of interest to examine their partial molal entropies, to see whether we can make a comparison between the values of the unitary terms. As mentioned above, the heat of precipitation of silver iodide was found by calorimetric measurement to be 1.16 electron-volts per ion pair, or 26,710 cal/mole. Dividing this by the temperature, we find for the entropy of solution of the crystal in the saturated solution the value... 

The equation just written is basic to calorimetric measurements. It allows you to calculate the amount of heat absorbed or evolved in a reaction if you know the heat capacity, Ccd, and the temperature change, At, of the calorimeter. 

Suppose reactants are mixed in a calorimeter at 25°C and the reaction heat causes the temperature of the products and calorimeter to rise to 35°C. The resultant determination of AH applies to what temperature Explain why it is desirable to keep the final temperature close to the initial temperature in a calorimetric measurement. 

This model does not say anything about the mechanism of triple-helix formation, because even in the case of an AON mechanism, nucleation may take place at many positions of the chains and may lead to products the chains of which are staggered. The AON model is based on the assumption that these products are too instable to exist in measurable concentration. As already mentioned, Weidner and Engel142 succeeded in proving by relaxation measurements of al CB2 that the kinetics of in vitro triple-helix formation is governed by more than one relaxation time. This rules out an AON mechanism, but the fitting to the experimentally found equilibrium transition curves nevertheless showed good accommodation and AH° computed from these curves could be confirmed by calorimetric measurement. 

Based on calorimetrically measured values given in Ref 7. We have arbitrarily used 1.00 kcal/g as the heat of detonation of TNT. For highly confmed TNT A = 1,09kcal/g and 1.03kcal/g for partially confmed TNT... 

They used electrochemical cell measurements to determine AmixGm, and solution calorimetric measurements to determine Am x//m. The results they obtained at T = 298.15 K are AmjXGm = 1060 J-mol 1 and Amjx//m = 340 J mol 1. 

Other methods can be used to obtain L and L2 from calorimetric measurements. For example, the derivation that lead to equations (5.33) and (5.34) in Chapter 5 for calculating V and V2 can be applied to give... 

P. A. G. O Hare, "Thermochemistry of Uranium Compounds XV. Calorimetric Measurements on UCI4, UOiCl . and UCFF . and the Standard Molar Enthalpy of Formation at 298.15 K of UC14", J. Chem. Thermodyn.. 17. 611-622 (1985). 

The electronic contribution is generally only a relatively small part of the total heat capacity in solids. In a few compounds like PrfOHE with excited electronic states just a few wavenumbers above the ground state, the Schottky anomaly occurs at such a low temperature that other contributions to the total heat capacity are still small, and hence, the Schottky anomaly shows up. Even in compounds like Eu(OH)i where the excited electronic states are only several hundred wavenumbers above the ground state, the Schottky maximum occurs at temperatures where the total heat capacity curve is dominated by the vibrational modes of the solid, and a peak is not apparent in the measured heat capacity. In compounds where the electronic and lattice heat capacity contributions can be separated, calorimetric measurements of the heat capacity can provide a useful check on the accuracy of spectroscopic measurements of electronic energy levels. 

The thermochemical data for the sulfoxides, sulfones, sulfites and sulfates, derived from calorimetric measurements, are given in Tables 1-5. All entries in the tables were checked by examination of the original sources. Where available, data are given for the gas phase and either the liquid (lq) or solid (c) phase. Preference was given to gas and liquid phase data. 

Moreover, in many cases, a shift of Tg to lower values of temperature has been detected, but in these cases the quality of adhesion between phases may be the main reason for the reversing of this attitude 11,14). If calorimetric measurements are executed in the neighbourhood of the glass transition zone, it is easy to show that jumps of energies appear in this neighbourhood. These jumps are very sensitive to the amount of filler added to the matrix polymer and they were used for the evaluation of the boundary layers developed around fillers. 

A is the manufacturer s rated activity based on calorimetric measurement of the heat evolved by the source. Since one 3-m.e.v. alpha particle produces 3 X 104 ion pairs in air of 1 mg. sq. cm. 1 density we calculate 7, the number of ion pairs produced per second above the leak in 1 cc. air at p torr pressure as ... 

It should be pointed out that a finite residual entropy calculated for a substance from experimental data obtained at temperatures extending down to a certain temperature, with extrapolation below that point, may arise either from failure of the experimenter to obtain thermodynamic equilibrium in his calorimetric measurements or from error in the extrapolation. Measurements made under ideal conditions and extended to sufficiently... 

Dynamic calorimetric measurements were made on 10 mg samples in sealed aluminum pans over the temperature range 50°C to 220°C at 10°C/min using a Mettler thermoanalytical system consisting of a DSC, model 20 and processor, model TC-lOA, which performed the data handling. 

A new acidity scale has been developed based on calorimetric measurement of A-methylimidazole and A-methylpyrrole in bulk solvents. A revised version of this method was shown to give better results in some cases. Another scale of solvent acidities was developed based on the hydrogen-bond donor acidities in aqueous DMSO. ... 

Calorimetry is an important technique in biology as well as in chemistry. The inventor of the calorimeter was Antoine Lavoisier, who is shown in the illustration. Lavoisier was a founder of modem chemistry, but he also carried out calorimetric measurements on biological materials. Lavoisier and Pierre Laplace reported in 1783 that respiration is a very slow form of combustion. Thus, calorimetry has been applied to biology virtually from its invention. 

Despite Lavoisier s early work on the link between energy and life, calorimetric measurements played a relatively minor role in biology until recent years, primarily because of practical obstacles. Every organism must take in and give off matter as part of its normal function, and it is very difficult to make accurate heat-flow measurements when matter is transferred. Moreover, the sizes of many organisms are poorly matched to the sizes of calorimeters. Although a chemist can adjust the amount of a substance on which to carry out calorimetry, a biologist often cannot. 

These are just some of the ways in which calorimetry is used in contemporary biological research. Our examples highlight studies at the cellular level, but ecologists also use calorimetry to explore the energy balances In ecosystems, and whole-organism biologists have found ways to carry out calorimetric measurements on fish, birds, reptiles, and mammals. Including humans. 

Equation can also be used to calculate the standard enthalpy of formation of a substance whose formation reaction does not proceed cleanly and rapidly. The enthalpy change for some other chemical reaction involving the substance can be determined by calorimetric measurements. Then Equation can be used to calculate the unknown standard enthalpy of formation. Example shows how to do this using experimental data from a constant-volume calorimetry experiment combined with standard heats of formation. 

On the other hand, Arnett and his coworkers have reported both the enthalpies of the protonation (AHJ and the hydrogen bond (AHf) for acid-base reactions. They calculated Hj by measuring the association constants for the proton transfer (ionization) in a number of bases by using FSO3H as the acid and determined Ai/j by calorimetric measurements of the heat of dissolution of P-FC6H4OH in various hydrogen bond acceptors, including sulphoxides, in They have also tried to correlate and... 

The worst hazard scenarios (excessive temperature and pressure rise accompanied by emission of toxic substances) must be worked out based upon calorimetric measurements (e.g. means to reduce hazards by using the inherent safety concept or Differential Scanning Calorimetry, DSC) and protection measures must be considered. If handling hazardous materials is considered too risky, procedures for generation of the hazardous reactants in situ in the reactor might be developed. Micro-reactor technology could also be an option. Completeness of the data on flammability, explosivity, (auto)ignition, static electricity, safe levels of exposure, environmental protection, transportation, etc. must be checked. Incompatibility of materials to be treated in a plant must be determined. 

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