Question

For a complex reaction _______________

• A. order of overall reaction is greater than molecularity of the slowest step.
• B. order of overall reaction is same as molecularity of the slowest step.
• C. order of overall reaction is less than the molecularity of the slowest step.
• D. Molecularity of the slowest step is never zero or non-integer.

Answer 1

Answer: (B), (D)

Molecularity of the slowest step is never zero or non-integer.

Complex reaction refers to a reaction whose mechanism consists of more than one elementary step. In simpler terms, when the whole reaction does not complete in one step, it means it occurs as a complex reaction or in many steps, in which order may not be equal to molecularity of reaction.

Order of a complex reaction can be determined experimentally by the slowest step. Order of a reaction is an experimental quantity. It can be zero and even a fraction but molecularity cannot be zero or a non-integer.

For a complex reaction, order of overall reaction = molecularity of slowest step. The rate of overall reaction depends upon the total number of molecules involved in the slowest step of the reaction. Hence, the molecularity of the slowest step is equal to the order of overall reaction.

The molecularity is the number of the reacting species (atoms, molecules) in a reaction occurring in a single step. These are the species that collide to form a product. Thus, the molecularity of a complete reaction can never be zero or non-integer.

Hence, options (A) and (D) are correct.