Gases quantitative studies

Computer simulation techniques offer the ability to study the potential energy surfaces of chemical reactions to a high degree of quantitative accuracy [4]. Theoretical studies of chemical reactions in the gas phase are a major field and can provide detailed insights into a variety of processes of fundamental interest in atmospheric and combustion chemistry. In the past decade theoretical methods were extended to the study of reaction processes in mesoscopic systems such as enzymatic reactions in solution, albeit to a more approximate level than the most accurate gas-phase studies. 

The choice of a particular type of gas discharge for quantitative studies of ion-molecule reactions is essential if useful information is to be obtained from ion abundance measurements. Generally, two types of systems have been used to study ion-molecule reactions. The pulsed afterglow technique has been used successfully by Fite et al. (3) and Sayers et al. (1) to obtain information on several exothermic reactions including simple charge transfer processes important in upper atmosphere chemistry. The use of a continuous d.c. discharge was initiated in our laboratories and has been successful in both exothermic and endothermic ion-molecule reactions which occur widely within these systems. 

Boyle also observed that heating a gas causes it to expand in volume, but more than a century passed before Jacques-Alexandre-Cesar Charles reported the first quantitative studies of gas volume as a function of temperature. Charles found that for a fixed amount of gas, a graph of gas volume vs. temperature gives a straight line, as shown in Figure 5. In other words, the volume of a gas is directly proportional to its temperature ... 

K. D. R. Setchell, J. A. Ives, G. C. Cashmore and A. M. Lawson, On the homogeneity of stools with respect to bile-acid composition and normal day-to-day variations A detailed qualitative and quantitative study using capillary column gas chromatography-mass spectrometry, Clin. Chim. Acta, 1987, 162, 257. 

The study of the interactions between organic compounds and aUtali-metal cations, in the gas phase, is related to many topics such as ion solvation, catalysis and molecular recognition. Furthermore, mass spectrometry has been used for the analyses of organolithium compounds and supramolecular assemblies that contain lithium cations. Alkali cationization is an important ionization technique, implemented for the analyses of a wide range of organic compounds. Finally, gas-phase studies are also useful for the quantitative determination of lithium cation affinity. The interaction between lithium cation and organic substances is thus related to different aspects of gas-phase chemistry and mass spectrometry. 

Rowe, P.N., Nienow, A.W. and Agbim, A.J., A preliminary quantitative study of particle segregation in gas fluidised beds binary systems of near-spherical particles, Trans. Inst. Chem. Engrs., 50 (1972b) 324-333. 

The field emission microscope offers a very clear-cut and basically simple method of determining the mobility of adsorbates quantitatively. If it were possible to evaporate the gas under study from a suitable source (e.g., a heatable CuO filament for oxygen) in such a way that only a portion of the tip became contaminated, one could determine how, and at what temperatures of the tip, migration occurred. If one attempted to evaporate from a gas emitter placed on one side of the tip while the microscope tube was at room temperature, gas rebounding from the walls would instantly contaminate the whole tip and the experiment would fail. 

Quantitative studies of radiolytic and hydrolytic degradations of the malonamide-alkane-nitric acid system by potentiometric or gas chromatographic titrations gave the following results (48) ... 

Campo, E., Ferreira, V., Escudero, A., Marques, J. C., and Cacho, J. (2006). Quantitative gas chromatography-olfactometry and chemical quantitative study of the aroma of four Madeira wines. Anal. Chim. Acta 563,180-187. 

From the earliest days of quantitative inquiry, scientists have sought to uncover the mathematical relationships that describe natural phenomena, including the properties of gases. Because there are four fundamental properties of a gas, namely, P, T, V, and n, discovering the relationship between any two requires that the other two properties be kept constant. Some of the earliest quantitative studies of gases were reported in the mid-1600s by British chemist Robert Boyle, who found that for a fixed amount of a gas at a specific temperature (i.e., constant n and T), the volume was inversely proportional to the applied pressure. This V-P relationship, known as Boyle s law, is represented as... 

Oxygen and tungsten reacted in a totally different manner. A minute pressure of oxygen formed an adsorbed film over the whole surface of the filament. The presence of this film was shown in three different ways it was found to diminish the thermionic emission of electrons from the heated wire at 1,500° K. it was found to inhibit the dissociation of hydrogen at the surface of the wire and it was shown by quantitative studies that the rate of reaction of the filament covered by adsorbed oxygen, with further supplies of the gas, was so great as to require the presence of a monatomic film of adsorbed oxygen, already combined with the surface of the filament for, p. 1150). 

Rowe, P. N., Nienow, A. W., and Agbim, A. J., A Preliminary Quantitative Study of Particle Segregation in Gas Fluidized Beds—Binary Systems of Near-Spherical Particles, Trans, lnstn. Chem. Engrs. 50,324 (1972b). 

Quantitative study of gas diffusion process from a single bubble under the action of capillary pressure is a more complex task. Bubble sizes at which diffusion rate would be sufficiently high and when it is possible to observe the decrease in their size, are very small (R < 0.1 cm). The only reliable method for determination of the thickness of films of such bubbles is the optical one. However, it should be kept in mind that the film thickness of... 

Fumed silica acts as a highly reinforcing filler in silicone elastomers. Its activity results fi-om its highly dispersed particle structure, high surface area and surface energy. To better understand the interplay of these properties first studies on gas adsorption of hexamethylsiloxane on hydrophilic and silylated silica have been conducted. The shape of the adsorption isotherm revels the existence of low- and high-energy adsorption sites, the latter qualitatively seem to be related to reinforcement of the silicone elastomer. Further quantitative studies in this field are needed. 

The main problem in the design of tubular reactors for quantitative studies of homogeneous reactions is to confine the reaction sharply to the reactor itself. This requires rapid mixing of the reactants at the entry, and equally excellent quenching of the exiting fluid. Both are easier to achieve for liquid-phase than for gas-phase reactions. Tubular reactors are not suited for gas-liquid reactions because gas sparging would disrupt the flow pattern. 

For quantitative studies, a tubular reactor, like a CSTR, must be operated at a constant and accurately known flow rate, requiring respective equipment. Also, as a rule, the evaluation presumes negligible pressure drop and ideal plug flow. The first of these rarely poses problems, except for gas-phase reactions at very low pressures. The second is an idealization and calls for a reasonably large reactor diameter. 

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