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A first order reaction depends on the concentration of only one reactant (a unimolecular reaction). Other reactants can be present, but their concentration has no effect on the rate. The rate law for a first order reaction is [] = [], The unit of k is s −1. [14]
The lowest-order contribution comes from the first nontrivial term e −S F X in the Taylor expansion of the action. Wick's theorem requires that the momenta in the X half-lines, the φ ( k ) factors in X , should match up with the momenta of the external half-lines in pairs.
Since the reaction rate determines the reaction timescale, the exact formula for the Damköhler number varies according to the rate law equation. For a general chemical reaction A → B following the Power law kinetics of n-th order, the Damköhler number for a convective flow system is defined as:
The units of the pre-exponential factor A are identical to those of the rate constant and will vary depending on the order of the reaction. For a first-order reaction, it has units of s −1. For that reason, it is often called frequency factor.
The hypothesis that reaction rate is proportional to reactant concentrations is, strictly speaking, only true for elementary reactions (reactions with a single mechanistic step), but the empirical rate expression = [] [] is also applicable to second order reactions that may not be concerted reactions. Guldberg and Waage were fortunate in that ...
For the NO 2 –CO reaction above, the rate depends on [NO 2] 2, so that the activated complex has composition N 2 O 4, with 2 NO 2 entering the reaction before the transition state, and CO reacting after the transition state. A multistep example is the reaction between oxalic acid and chlorine in aqueous solution: H 2 C 2 O 4 + Cl 2 → 2 CO 2 ...
Chemical kinetics, also known as reaction kinetics, is the branch of physical chemistry that is concerned with understanding the rates of chemical reactions. It is different from chemical thermodynamics, which deals with the direction in which a reaction occurs but in itself tells nothing about its rate.
The Lindemann mechanism is used to model gas phase decomposition or isomerization reactions. Although the net formula for decomposition or isomerization appears to be unimolecular and suggests first-order kinetics in the reactant, the Lindemann mechanism shows that the unimolecular reaction step is preceded by a bimolecular activation step so ...