What is pre-exponential factor formula?
The Arrhenius equation is k = Ae^(-Ea/RT), where A is the frequency or pre-exponential factor and e^(-Ea/RT) represents the fraction of collisions that have enough energy to overcome the activation barrier (i.e., have energy greater than or equal to the activation energy Ea) at temperature T.
How large is the pre-exponential factor?
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.
What is rate exponent in fluent?
Rate Exponent specifies the rate constant for the reactant species in the reaction. Number of Products indicates the number of products in the specified reaction.
Can pre-exponential be negative?
Given that the pre-exponential factor of the Arrhenius equation is always positive (otherwise, you would potentially have a rate constant of 0, meaning the reaction never occurs), the rate constant is never negative.
Can the activation energy be negative?
Negative activation energy is possible even for elementary reactions. In these cases there are attractive forces between reactants, there are no barrier, or the barrier is submerged. This means you must find complexes between the reactants and submerged barrier.
What is eddy dissipation model?
The eddy dissipation model, based on the work of Magnussen and Hjertager, is a turbulent-chemistry reaction model. Most fuels are fast burning and the overall rate of reaction is controlled by turbulence mixing. In this model, the chemical reaction is governed by large eddy mixing time scale.
What is finite rate chemistry?
Finite rate chemistry models assume nothing about the flow or flame but attempt to solve the species equations using models for the low-pass filtered reaction rates.
What does pre-exponential factor depend on?
The units of the pre-exponential factor vary depending on the order of the reaction. In first order reactions, the units of the pre-exponential factor are reciprocal time (e.g., 1/s). Because the pre-exponential factor depends on frequency of collisions, it is related to collision theory and transition state theory.
How do you find the pre-exponential factor in the Arrhenius equation?
The slope of the Arrhenius plot can be used to find the activation energy. The Arrhenius plot can also be used by extrapolating the line back to the y-intercept to obtain the pre-exponential factor, A. This factor is significant because A=p×Z, where p is a steric factor and Z is the collision frequency.