Define the following terms:
$(1)$ Fraction of molecules
$(2)$ Frequency factor

(N/A) $(1)$ Fraction of molecules: It is defined as the ratio of the number of molecules having energy equal to or greater than the activation energy $(E_a)$ to the total number of molecules present in the system. It is given by the expression $f = e^{-E_a/RT}$.
$(2)$ Frequency factor: Also known as the pre-exponential factor $(A)$,it represents the frequency of collisions between reactant molecules. It is a constant specific to a particular reaction and is related to the total number of collisions per unit volume per unit time.