Diameter of molecules

The influence of interchannel dlffusional limitation may be estimated by a comparison of catalyst para-selectivities to separate product molecules, the diameters of which are different. As is known, the kinetic diameter of molecules increases in the sequence para-XYI para-selectivities to dial-... 

A quantity much used in kinelic theory is the "mean free path." which is the average distance traversed by a molecule between collisions. There are ways of calculating this and also the effective diameters of molecules, and these data lead to many conclusions as to frequency of collisions and rate of diffusion... 

On the first stage of hydrogenation reaction the C/H composition of fulleranes can be approximately determined by XRD from increase of unit cell parameter. The crystal structure of fulleranes powder remains to be fee like in pristine C60 but the cell parameter increases proportionally to the number of attached hydrogen atoms due to increase of van der Waals diameter of molecules. Using chemical analysis on carbon/hydrogen ratio performed on samples hydrogenated at various conditions we constructed the dependence which could be used for approximate evaluation of hydrogen content from known cell parameter determined from powder XRD, see Fig. 5.3... 

The pores of zeolites are of molecular dimensions (Fig. 1). In principle molecules can be excluded from the pores if their diameter is larger than the pore apertures. The zeolite framework is, however, not a rigid structure. Especially at higher temperatures, the pores become more flexible. As a result, molecules with larger diameters than the dimensions of the pores will be able to penetrate the channels. The maximum diameter of molecules that are able to adsorb within the zeolite is called the adsorption cutoff diameter. This diameter is about 0.95 nm for zeolite X and Y [30], 0.65 nm for ZSM-5 [30], and 0.4 nm for zeolite-4 A [1] at 3(X) K. This means that, in principle, all molecules listed in Fig. 1 can permeate through a zeolitic membrane made from zeolite X, Y or ZSM-5, except for the large amines. Complete exclusion of molecules from the pores will therefore occur only when using a zeolite-A membrane. 

A simple two-component relationship for hERG blocking potency was proposed by Aptula and Cronin [37], A set of 150 descriptors were calculated for 19 structurally diverse hERG blockers from the literature. The calculated variables included physicochemical parameters, topological indexes, and quantum chemical descriptors. Multiple linear regression was used to derive a relationship between hERG blocking potency and two descriptors, -log D and Dmax (the maximum diameter of molecules) ... 

Rate of entropy production due to diffusion (Chapter 2) [J/m s K] Characteristic diameter of molecule (Section 4.1) [A]... 

As expected, the constant a depends on the attractive interactions, and b on the diameter of molecules, and thus b is the repulsive contribution to the pair potential (see also Sections 2.6.2 and 2.7). 

Collision diameter of molecule, determined from viscosity... 

Molecular sieves arc aluminum silicate ion exchangers, whose pore size depends on the kind of cation present. Commercial preparations of these materials arc available in particle sizes of 40 to 60 mesh to 00 to 120 mesh. The sieves are classified according to the maximum diameter of molecules that can enter the pores. Commercial molecular sieves come in pore sizes of 4, 5, 10, and 1,1 A, Molecules smaller than Ihese dimensions penetrate into the interior of the panicles where adsorption takes place. For such molecules, the surface area is enormous when compared with the area available to larger molecules. Thus, molecular sieves can be used to separate small molecules from large. For... 

A French physicist, Jean Baptiste Perrin (1870-1942), made the necessary measurements in 1908 and produced the first hard and fast estimate of the diameter of molecules and, therefore, of atoms. Since the Brownian motion was a reasonably direct... 

Knudsen diffusion exists in middle pore diameters (10-1.000 A) where the mass transport happens by collision between the molecules and the wall. Configuration diffusion exists in pores where the diameter of molecules is of the same order of the pore diameter. 

The collision diameter (Xu of binary pair k-l can be estimated as an arithmetic average of collision diameters of molecules as... 

APab Appearance potential of gaseous molecule d Diameter of molecule... 

Let us carry out an imaginary experiment. Consider the very beginning of melting process (in the ideal case) when on the crystal surface, at first, the film with a thickness h of one molecule appears, then of two molecules, of three molecules and so on. Let us put a question at which stage (Le., by which critical thickness lie of a film) do the structural elements of liquid arise We consider, for the simplicity, that the structure elements are only isometric clusters which can be ap>proximated by spheres of a certain diameter dci. It is obvious, that the relation dci>dmoi, where dmoi is the diameter of molecule, take place even for the very small clusters. The clusters cannot arise till the film thickness is smaller of cluster diameter they simply could not get in. Moreover, one must take into account that the formation of three-dimensional structure elements of liquid is a statistical process it is possible only when a certain freedom of the movement of molecules in the all three dimensions takes place. Taking into consideration this condition (dimension factor), we come to the following inequality ... 

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