Calorimetric Experiment

The validity of equation (A2.1.70) has sometimes been questioned when enthalpies of reaction detennined from calorimetric experiments fail to agree with those detennined from the temperature dependence of the equilibrium constant. The thennodynamic equation is rigorously correct, so doubters should instead examine the experunental uncertainties and whether the two methods actually relate to exactly the same reaction. 

The elemental compositions of the oxidized oil sands produced from our calorimetric experiments at 285°C have been determined. 

Calorimetric experiments on fixed proteins demonstrate with certainty that the process of fixation both elevates the mean denaturation temperature of... 

Provided that the time-temperature curve obtained from the calorimetric experiments is wholly of first-order, or comprises a first-order section, usually after the inflection point of sigmoid reaction curves, a conventional analysis yields a first-order rate constant ku which is related to the concentration of monomer, m, and the initial concentration of initiator, c0, by the equations... 

In the bomb process, reactants at the initial pressure pi and temperature 7 are converted to products at the final pressure pf and temperature Tf. The primary goal of a combustion calorimetric experiment, however, is to obtain the change of internal energy, Ac//°(7r), associated with the reaction under study, with all reactants and products in their standard states pi = pf = O.IMPa) and under isothermal conditions at a reference temperature 7r (usually 298.15 K). Once AC//°(298.15K) is known, it is possible to derive the standard enthalpy of combustion, AC77°(298.15K), and subsequently calculate the standard enthalpy of formation of the compound of interest from the known standard enthalpies of formation of the products and other reactants. 

The maximum permissible value of Af may vary for different calorimetric experiments. Typically, At < 15 s. 

Titration calorimetry is a method in which one reactant inside a calorimetric vessel is titrated with another delivered from a burette at a controlled rate. This technique has been adapted to a variety of calorimeters, notably of the isoperibol and heat flow types [194-198]. The output of a titration calorimetric experiment is usually a plot of the temperature change or the heat flow associated with the reaction or physical interaction under study as a function of time or the amount of titrant added. 

Figure 11.2 Typical temperature-time curve for an isoperibol continuous titration calorimetric experiment involving an exothermic process.

To our knowledge, the question of the standard state corrections in DSC experiments has never been addressed. These corrections may in general be negligible, because most studies only involve condensed phases and are performed at pressures not too far from atmospheric. This may not be the case if, for example, a decomposition reaction of a solid compound that generates a gas is studied in a hermetically closed crucible, or high pressures are applied to the sample and reference cells. The strategies for the calculation of standard state corrections in calorimetric experiments have been illustrated in chapter 7 for combustion calorimetry. 

R. N. Goldberg, R. L. Nuttall, E. J. Prosen, A. P. Brunetti. Digital Data Acquisition and Computer Computation Applied to Calorimetric Experiments. Nat. Bur. Stand. Report 1971, 10437. 

A great deal of adsorption work has been carried out using titanium dioxide as an adsorbent, following extensive work with this material by Harkins and Jura 169). In one series of accurate calorimetric experiments, the initial temperature of evacuation was 300° C. 96). Any grease present on the rutile before degassing would not have been removed by this treatment. Recent work 170) has shown that it is possible that rutile may be subject to hydrocarbon contamination. 

The observed enthalpy contribution (in units of calories) due to breaking up the BCCI4 complex in a calorimetric experiment would become ... 

The enthalpy of formation of HNF2 is known from a reaction calorimetric experiment to be — 65 6 kJmol. The enthalpy of formation of NH2F remains unknown from experiment but the value has been suggested to be ca —58 kJmol. We must thus content ourselves with the two values of formation of l-aza-2,8-dioxabicyclo[3.3.0]octane, — 10 and +16 kJmol, which, given all of our assumptions, are not that disparate. 

The effect of temperature on ammonia adsorption by ZSM5 samples has been investigated by microcalorimetry, varying the adsorption temperature from 150 to 400°C [235]. The initial heats of adsorption were independent of temperature up to 300°C. When the adsorption temperature increased, there was a competition between the formation of ammonium ions on Brpnsted sites and their decomposition. The total number of titrated sites decreased with increasing adsorption temperature. It appeared that an adsorption temperature between 150 and 300°C is appropriate for these calorimetric experiments. 

Seki and Tirrell [436] studied the pH-dependent complexation of poly(acrylic acid) derivatives with phospholipid vesicle membranes. These authors found that polyfacrylic acid), poly(methacrylic arid) and poly(ethacrylic acid) modify the properties of a phospholipid vesicle membrane. At or below a critical pH the polymers complex with the membrane, resulting in broadening of the melting transition. The value of the critical pH depends on the chemical structure and tacticity of the polymer and increases with polymer hydro-phobicity from approximately 4.6 for poly(acrylic acid) to approximately 8 for poly(ethacrylic acid). Subsequent photophysical and calorimetric experiments [437] and kinetic studies [398] support the hypothesis that these transitions are caused by pH dependent adsorption of hydrophobic polymeric carboxylic acids... 

In order to determine which mechanism actually governs the catalytic reaction, it is necessary to compare the rates of the slowest steps of both mechanisms. As in the case of NiO(200), calorimetric experiments show that adsorption of oxygen and formation of C03"(adS) ions (Interaction 1) are fast processes also on the surface of NiO(250). However, the following interactions are slower processes. 

One possible reason suggested by Flory and Mandelkern (1956) for or contribution to the discrepancies indicated in Table 2 is the inability of the penetrometer method to detect the maximum temperature of melting because of its relative insensitivity and because of the upper "tail to the crystallinity-temperature curve as deduced from the copolymer crystallinity theory of Flory (1955). Dole and Wunderlich (1957, 1959) found, however, that two melting regions each of the quenched 80/20 and 60/40 copolymers could be observed in the calorimetric experiments. The specific heat curves of these two copolyesters are illustrated in... 

BaSi03 (gls.). Tschemobaeff1 reported Q = —41.0 for the reaction, Si02 (c) +BaC03(c) =BaSi03 (gls.) +C02 (g), from calorimetric experiments, and Jander1 calculated Q= —34.0 for the same reaction from equilibrium data. These data yield, for BaSi03 (gls.), Qf—359 and 366. See also Marchal.1... 

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