Question

In a bimolecular reaction, the steric factor P was experimentally determined to be 4. 5. The correct option(s) among the following is(are)

• A. The value of the frequency factor predicted by the Arrhenius equation is higher than that determined experimentally.
• B. The activation energy of the reaction is unaffected by the value of the steric factor.
• C. Since P = 4.5, the reaction will not proceed unless an effective catalyst is used.
• D. The experimentally determined value of the frequency factor is higher than that predicated by the Arrhenius equation.

Answer 1

Answer: (B), (D)

Options B and D

Answer 2

Solution Explanation:

1. The Arrhenius equation is written as
     $k = A \exp\left(\frac{-E_a}{RT}\right)$.
     Here, the activation energy $E_a$ is independent of the steric factor $P$.
2. In collision theory, the frequency factor is given by
     $A_{\text{theo}} = Z$ (from molecular collisions).
     To account for proper molecular orientation and other effects, a steric factor $P$ is introduced so that
     $A_{\text{exp}} = P \cdot Z$.
3. With $P = 4.5$ (i.e. $>1$), the experimental frequency factor $A_{\text{exp}}$ is 4.5 times larger than the basic collision frequency $Z$.
4. Hence, the activation energy is unaffected by $P$ (making Option B true) and the experimentally determined frequency factor is higher than the value predicted by simply using collision frequency (making Option D true).

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Answer: Options B and D