Effect of Chemical Forces on Physical Properties

Now how curiously our ideas expand by watching these conditions of the attraction of cohesion — how many new phenomena it gives us beyond those of the attraction of gravitation  

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Effect of Chemical Forces on Physical Properties Table 4.3 Continued... 

Beside the chemical composition, the crystalline structure of the mineral has an important effect on the adsorption ability of its surface. This is due to the fact that lattice bindings are usually not equivalent and space disproportions occur, so that fission surface areas have specific properties. Typical examples are layer lattices of graphite or talc where the main valences proceed in the layer plains whereas these are interconnected with feeble valences. Fission areas of such minerals are hydrophobic. The effect of the structure on adsorption properties of a mineral surface increases with increasing adsorption density and with decreasing force of the adsorption binding of the solid phase5. A crystalline lattice contains structural defects (which include physical and chemical surface imperfections and deficiencies in the volume phase) which can influence the chemical reactivity of a crystal surface. 

Molecular simulation techniques can obtain the microscopic information that cannot be detected by current experimental conditions, but the conventional simulation methods stiU have inherent limitations with special mesoscopic scales of various complex forces and complex structure. It is necessary to establish a new mesoscale method that considers the chemical reaction and transport to the larger system at the same time. The roughness and chemical properties of catalyst supporting interface have great influence on chemical and physical adsorption stability of clusters. The problem is that the system is too large for traditional simulation in nano-/micro-/mesoscale. We need a new mesoscale method to study the effect of interface roughness on physical/chemistry phenomena. 

In a recent article [5] dealing with the properties of adsorbed water layers and the effect of adsorbed layers on interparticle forces, it was clearly stated that even under common room conditions (relative humidity in the region 40-60%), two or three adsorbed monolayers of water are often present on particles, dominating the interactions, and therefore the physical characteristics of the material. For a two-phase equilibrium system containing hydrophilic silica plates (surface of a-quartz covered by silanol groups) and water molecules, a molecular dynamic simulation expected at least one adsorbed monolayer to be present. Quite different behavior would be expected for less hydrophilic surfaces. The material character and chemical properties of solid materials are of crucial importance in the hydration interaction. Therefore, some common adsorbents which are Irequently used in aqueous electrolyte solutions are discussed separately. 

Substitution of fluorine for hydrogen in an organic compound has a profound influence on the compound s chemical and physical properties. Several factors that are characteristic of fluorine and that underHe the observed effects are the large electronegativity of fluorine, its small size, the low degree of polarizabiHty of the carbon—fluorine bond and the weak intermolecular forces. These effects are illustrated by the comparisons of properties of fluorocarbons to chlorocarbons and hydrocarbons in Tables 1 and 2. 

Inter- and intramolecular forces (imf) are of vital importance in the quantitative description of structural effects on bioactivities and chemical properties. They can make a significant contribution to chemical reactivities and some physical properties as well. Types of intermolecular forces and their present parameterization are listed in Table 750. 

There can be, however, no doubt that in catalytic processes, purely physical factors play an important role, in addition to the chemical valence forces. This is particularly true for the solid catalysts of heterogeneous reactions for which the properties of surfaces, as the seats of catalytic action are of prime importance. The total surface areas, the fine structure of the surfaces, the transport of reactants to and from surfaces, and the adsorption of the reactants on the surfaces, can all be considered as processes of a predominantly physical nature which contribute to the catalytic overall effect. Any attempt, however, to draw too sharp a line between chemical and physical processes would be futile. This is illustrated clearly by the fact that the adsorption of gases on surfaces can be described either as a mere physical condensation of the gas molecules on top of the solid surface, as well as the result of chemical affinities between adsorbate and adsorbent. Every single case of adsorption may lie closer to either one of the hypothetical extremes of a purely physcial or of a purely chemical adsorption, and it would be misleading to maintain an artificial differentiation between physical and chemical factors. 

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