Question

State a condition under which a bimolecular reaction is kinetically first-order reaction. Give an example. For which type of reactions, do order and molecularity have the same value?

Hint:

In elementary reactions, the order and molecularity are always equal, as the order corresponds to the number of molecules involved in the rate-determining step.

Answer 1

For a bimolecular reaction to be first order, the rate of the reaction must be directly proportional to the concentration of one reactant. This occurs in cases like a simple reaction between two molecules where the reaction rate is determined by the concentration of just one of the reactants. An example is the reaction between hydrogen and iodine to form hydrogen iodide, which is first-order with respect to hydrogen and iodine. The order and molecularity of elementary reactions, such as the reaction of two molecules of a reactant, will always be the same.