Arrhenius Equation and the Pre-Exponential Factor (A)
We already discussed that A is known as the pre-exponential factor in the Arrhenius equation. This factor deals with intermolecular collisions and can be thought of as the frequency of precisely aligned collisions between molecules with sufficient energy to initiate a chemical reaction.
A = ρZ
where
Z represents the frequency factor
ρ represents the steric factor
The value of A has different values for different reactions and must be determined experimentally. It also depends on the temperature at which the reaction takes place. The units of A depend on the order of reactions. For example, the units of ‘A’ for the second order rate constant are Lmol-1s-1 whereas the units of the first order rate constant are s-1.
Arrhenius Equation
The Arrhenius equation establishes a link between a chemical reaction’s rate constant and absolute temperature, incorporating the A factor, or pre-exponential factor. This factor represents the frequency of reactant particles colliding in the correct orientation. The equation highlights how reaction rates are influenced by changes in temperature, illustrating the temperature dependency of chemical processes. Let us look at the Arrhenius equation in detail in this article.