Chemical Kinetics — Chemistry STD 12 Science — Question
Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryChemical Kinetics3 Marks
Question
What is a frequency factor or pre-exponential factor?
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Answer
In Arrhenius equation, $k=A \times e^{-E_3 / R T}$ the factor $A$ is called frequency factor and since it is a coefficient of exponential expression, $e \sim Ea / RT$ it is also called a pre-exponential factor.
In the above equation $k$ is a rate constant at temperature $T, E_a$ is the energy of activation and $R$ is a gas constant.
A is related to frequency of collisions $(Z)$ or rate of collisions. It is represented as, $A=P \times Z$ where $P$ is the probability of collisions with proper orientations and $Z$ is the frequency of collisions of reacting molecules.
The units of $A$ are same as that of $k$.
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