= Pre-exponential factor
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= Arrhenius prefactor
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{synonym}
= Frequency factor
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The <pre-exponential factor> multiplies the <exponential function> in the <Arrhenius equation>. It has the same units as the <rate constant>, so for a <first-order reaction> both have units $\mathrm{s^{-1}}$. Its physical interpretation depends on the <reaction mechanism>; an assumed constant $A$ should not be identified with a universal collision frequency. Comparing <activation energies> alone does not rank absolute <rate constants> when the <pre-exponential factors> differ. See the <IUPAC Compendium of Chemical Terminology (Gold Book) by International Union of Pure and Applied Chemistry/pre-exponential factor>.
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