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b) The straight portion of the graph for substrate concentration over time is indicative of a zero-order dependence on substrate for most of the reaction, but the curve at low [A] is indicative of a change to (in this case) a first-order dependence on [A].
The rate of enzymatic reaction increases with the increase of the substrate concentration up to a certain level called V max; at V max, increase in substrate concentration does not cause any increase in reaction rate as there is no more enzyme (E) available for reacting with substrate (S).
A reaction can also have an undefined reaction order with respect to a reactant if the rate is not simply proportional to some power of the concentration of that reactant; for example, one cannot talk about reaction order in the rate equation for a bimolecular reaction between adsorbed molecules:
The Michaelis constant has units of concentration, and for a given reaction is equal to the concentration of substrate at which the reaction rate is half of . [6] Biochemical reactions involving a single substrate are often assumed to follow Michaelis–Menten kinetics, without regard to the model's underlying assumptions.
After van 't Hoff, chemical kinetics dealt with the experimental determination of reaction rates from which rate laws and rate constants are derived. Relatively simple rate laws exist for zero order reactions (for which reaction rates are independent of concentration), first order reactions, and second order reactions, and can be derived for ...
As an example, consider the gas-phase reaction NO 2 + CO → NO + CO 2.If this reaction occurred in a single step, its reaction rate (r) would be proportional to the rate of collisions between NO 2 and CO molecules: r = k[NO 2][CO], where k is the reaction rate constant, and square brackets indicate a molar concentration.
[] = [] In order to find the half-life, we have to replace the concentration value for the initial concentration divided by 2: [] / = [] / and isolate the time: / = [] This t ½ formula indicates that the half-life for a zero order reaction depends on the initial concentration and the rate constant.
The steady state approximation, [1] occasionally called the stationary-state approximation or Bodenstein's quasi-steady state approximation, involves setting the rate of change of a reaction intermediate in a reaction mechanism equal to zero so that the kinetic equations can be simplified by setting the rate of formation of the intermediate equal to the rate of its destruction.