Concentration, effect on rate reaction

Concentration effect on reaction rate Temperature effect on reaction rate Surface area effect on reaction rate Chemical equilibrium conditions Simultaneous forward and reverse reaction Rate forward reaction = rate reverse reaction Reaction system is closed ... 

Reaction rate limited (zero-order kinetics). In this case, the biofilm concentration has no effect on reaction rate, and the biodegradation breakthrough curve is linear. 

When the gold surface is completely covered with HI molecules, increasing the concentration of HI(g) has no effect on reaction rate. 

Combining volumes, law of, 26, 236 Combustion, heat of hydrogen, 40 Complex ions, 392 amphoteric, 396 bonding in, 395 formation, 413 geometry of. 393 in nature, 396 isomers, 394 linear, 395 octahedral, 393 significance of, 395 square planar, 395 tetrahedral, 394 weak acids, 396 Compound, 28 bonding in, 306 Concentration and equilibrium, 148 and E zero s, 213 and Le Chatelier s Principle, 149 effect on reaction rate, 126, 128 molar, 72... 

What effect does concentration have on reaction rate ... 

It is easy to understand the lower reactivity of non-ionic nucleophiles in micelles as compared with water. Micelles have a lower polarity than water and reactions of non-ionic nucleophiles are typically inhibited by solvents of low polarity. Thus, micelles behave as a submicroscopic solvent which has less ability than water, or a polar organic solvent, to interact with a polar transition state. Micellar medium effects on reaction rate, like kinetic solvent effects, depend on differences in free energy between initial and transition states, and a favorable distribution of reactants from water into a micellar pseudophase means that reactants have a lower free energy in micelles than in water. This factor, of itself, will inhibit reaction, but it may be offset by favorable interactions with the transition state and, for bimolecular reactions, by the concentration of reactants into the small volume of the micellar pseudophase. 

The high ionic concentration at the micellar surface may result in an ionic strength effect on reaction rate. Salt effects in water, however, are generally smaller for ion-molecule reactions than for reactions which involve an increase or decrease of charge, and they should be approximately zero in the... 

Substrate concentration is yet another variable that must be clearly defined. The hyperbolic relationship between substrate concentration ([S ) and reaction velocity, for simple enzyme-based systems, is well known (Figure C1.1.1). At very low substrate concentrations ([S] ATm), there is a linear first-order dependence of reaction velocity on substrate concentration. At very high substrate concentrations ([S] A m), the reaction velocity is essentially independent of substrate concentration. Reaction velocities at intermediate substrate concentrations ([S] A"m) are mixed-order with respect to the concentration of substrate. If an assay is based on initial velocity measurements, then the defined substrate concentration may fall within any of these ranges and still provide a quantitative estimate of total enzyme activity (see Equation Cl. 1.5). The essential point is that a single substrate concentration must be used for all calibration and test-sample assays. In most cases, assays are designed such that [S] A m, where small deviations in substrate concentration will have a minimal effect on reaction rate, and where accurate initial velocity measurements are typically easier to obtain. 

Matrix effects can be complex and difficult to predict because most co-solutes may compete with the reactant of interest for reactions with radicals, becoming effective scavengers that reduce the sonochemical efficiency. Taylor et al. [30] have observed a significant inhibition of the sonolysis of polycyclic aromatic hydrocarbons (PAHs) in the presence of dissolved organic matter. Substrate concentration effects on the rate constants have also been reported. When the target molecules are volatile, they partition between... 

Since phosphates and sulfates with long chain alkyl substituents form micelles at concentrations above their CMC, the hydrolysis of these esters can be subject to micellar catalysis thereby providing a simplified system in which micelle formation and structure are not alfected by the presence of a foreign solubilizate. The hydrolysis of such surfactants must be considered, however, in investigations of their effects on reaction rates. Fortunately, the rate constants for the neutral hydrolysis of esters such as sodium dodecyl sulfate are extremely slow at 90° = 296 days at pH = 8-63), and the acid-catalyzed hydrolysis of the same ester is some three orders of magnitude faster and thus is still negligible in most cases (Kurz, 1962). 

Our knowledge of these factors influencing reaction rates is quite elementary in many respects. Direct study is difficult in many instances, because of the complex nature of the hydrous metal oxide surface. Much of our current understanding comes from using indirect methods. One useful approach is to make small changes in reactant structure, then examine the effect on reaction rate. Another approach is to systematically examine how reactant concentration, medium composition (pH and ionic strength), and the presence of other adsorbing solutes influence reaction rate. 

Temperature often has a major effect on reaction rate. As Figure 16.8A shows for a common organic reaction—hydrolysis, or reaction with water, of an ester—when reactant concentrations are held constant, the rate nearly doubles with each rise in temperature of 10 K (or 10°C). In fact, for many reactions near room temperature, an increase of 10°C causes a doubling or tripling of the rate. 

The aspartate-histidine-serine combination, referred to as the catalytic triad, is an example of cooperative interactions between amino acid residues in the active site. The strong nucleophilic attacking group created by this charge-relay system has the same general effect on reaction rate as increasing the concentration of hydroxyl ions available for collision in the uncatalyzed reaction. 

Inorganic salt hydrates can be used to maintain controlled water activities in the enzyme support and in the fluid phase. Chaudhary et al. used sodium pyrophosphate (Na4P207 X IOH2O) in fluoroform to adjust the water activity and to maximize the enzyme activity. They put the salt hydrate inside the batch reactor together with substrates and enzyme. They observed that the salt concentration had an effect on reaction rates, and therefore had to be optimized [49]. 

Most reactions that have been investigated using PTC in supercritical fluids have been solid-SCF systems, not liquid-SCF. The first published example of PTC in an SCF is the displacement reaction of benzyl chloride 1 with potassium bromide in supercritical carbon dioxide (SCCO2) with 5 mol % acetone, in the presence of tetraheptylammonium bromide (THAB) [19-20] (Scheme 4.10-1) to yield benzyl bromide 2. The effects on reaction rate of traditional PTC parameters, such as agitation, catalyst type, temperature, pressure, and catalyst concentration were investigated. The experimental technique is described below. PTC appeared to occur between an SCF phase and a solid salt phase, and in the absence of a catalyst the reaction did not occur. With an excess of inorganic salt, the reaction was shown to follow pseudo-first order kinetics. 

It is to be noted that at high steam concentrations the rate is approximately first order in propylene as well as in oxygen. Water vapor has an inhibiting effect on reaction rate, but it is relatively greater on the COg production, and therefore the selectivity is improved—as has been known for some time from patents. Consecutive oxidation of acrolein... 

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