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Iron rusting has a low reaction rate. This process is slow. Wood combustion has a high reaction rate. This process is fast. The reaction rate or rate of reaction is the speed at which a chemical reaction takes place, defined as proportional to the increase in the concentration of a product per unit time and to the decrease in the concentration of a reactant per unit time. [1]
It can increase the rate of reaction by a factor of up to 10 7. [15] In particular, it has been found that enzyme provides an environment which is more polar than water, and that the ionic transition states are stabilized by fixed dipoles.
In practice, if A and B interconvert with overall rate constants k f and k r, then for most practical purposes, the change in composition becomes negligible after t ~ 3.5/(k f + k r), or approximately five half-lives, and the system product ratio can be regarded as the result of thermodynamic control. In general, short reaction times favour ...
Most enzymes have a rate around 10 5 s −1 M −1. The fastest enzymes in the dark box on the right (>10 8 s −1 M −1) are constrained by the diffusion limit. (Data adapted from reference [1]) A diffusion-limited enzyme catalyses a reaction so efficiently that the rate limiting step is that of substrate diffusion into the active site, or ...
Beyond this limit the enzyme is saturated with substrate and the reaction rate ceases to increase. The reaction catalysed by an enzyme uses exactly the same reactants and produces exactly the same products as the uncatalysed reaction. Like other catalysts, enzymes do not alter the position of equilibrium between substrates and products. [1]
At the maximum reaction rate (V max) of the enzyme, all the enzyme active sites are bound to substrate, and the amount of ES complex is the same as the total amount of enzyme. [1]: 8.4 V max is only one of several important kinetic parameters. The amount of substrate needed to achieve a given rate of reaction is also important.
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In this case, experiments have determined that this reaction takes place according to the rate law = []. This form suggests that the rate-determining step is a reaction between two molecules of NO 2. A possible mechanism for the overall reaction that explains the rate law is: 2 NO 2 → NO 3 + NO (slow)