Question

According to various authentic sources, the rate law for elementary reactions is equal to the molecularity of the reaction. For instance, for the elementary reaction (aA + bB \rightarrow cC + dD), the rate law is given by R = k[A]^a[B]^b), where (k) is the rate constant and [⋅] represents concentration.

Are there any exceptions to this principle? Is there an elementary reaction where the rate law is not consistent with the molecularity, i.e., the order is not equal to the molecularity?

a. Yes, there are known cases of elementary reactions where the rate law does not align with the molecularity.
b. No, the rate law for elementary reactions is always consistent with the molecularity.
c. The relationship between rate law and molecularity in elementary reactions is not well-established and can vary.
d. Molecularity and order are terms used interchangeably, so the question itself is based on a misconception.

Answer 1

Yes, there are known cases of elementary reactions where the rate law does not align with the molecularity. Option a

Step-by-step explanation:

The answer to the question is a. Yes, there are known cases of elementary reactions where the rate law does not align with the molecularity. Although the rate law for elementary reactions is generally consistent with the molecularity, there are exceptions.

This means that there are cases where the order of the reaction, as determined experimentally from the rate law, does not match the molecularity of the reaction.

An example of an elementary reaction where the rate law is not consistent with the molecularity is the reaction between nitric oxide (NO) and oxygen (O2):

2 NO + O2 → 2 NO2

In this reaction, the rate law is R = k[NO]2[O2], which is consistent with a bimolecular reaction (molecularity of 2) as indicated by the number of reactant molecules present. However, the order of the reaction is determined experimentally to be second-order overall, which is not consistent with the molecularity. Option a