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The rate for a bimolecular gas-phase reaction, A + B → product, predicted by collision theory is [6] = = ()where: k is the rate constant in units of (number of molecules) −1 ⋅s −1 ⋅m 3.
It offers a concrete interpretation of the pre-exponential factor A in the Arrhenius equation; for a unimolecular, single-step process, the rough equivalence A = (k B T/h) exp(1 + ΔS ‡ /R) (or A = (k B T/h) exp(2 + ΔS ‡ /R) for bimolecular gas-phase reactions) holds. For a unimolecular process, a negative value indicates a more ordered ...
the reaction rate is described by = [] [], where is a bimolecular rate constant. Bimolecular rate constants have an upper limit that is determined by how frequently molecules can collide, and the fastest such processes are limited by diffusion. Thus, in general, a bimolecular rate constant has an upper limit of k 2 ≤ ~10 10 M −1 s −1. For ...
Depending on how many molecules come together, a reaction can be unimolecular, bimolecular or even trimolecular. The kinetic order of any elementary reaction or reaction step is equal to its molecularity, and the rate equation of an elementary reaction can therefore be determined by inspection, from the molecularity. [1]
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:
while for bimolecular gas reactions A = (e 2 k B T/h) (RT/p) exp(ΔS ‡ /R). In these equations e is the base of natural logarithms, h is the Planck constant, k B is the Boltzmann constant and T the absolute temperature. R′ is the ideal gas constant. The factor is needed because of the pressure dependence of the reaction rate.
The Eyring equation (occasionally also known as Eyring–Polanyi equation) is an equation used in chemical kinetics to describe changes in the rate of a chemical reaction against temperature. It was developed almost simultaneously in 1935 by Henry Eyring , Meredith Gwynne Evans and Michael Polanyi .
Reactions on surfaces are reactions in which at least one of the steps of the reaction mechanism is the adsorption of one or more reactants. The mechanisms for these reactions, and the rate equations are of extreme importance for heterogeneous catalysis .