What is the Difference Between Unimolecular and Bimolecular Reactions?

The main difference between unimolecular and bimolecular reactions lies in the number of reactant molecules involved in the reactions.

• Unimolecular reactions involve only one molecule as a reactant, meaning that a single molecule undergoes a reaction and is converted to products. These reactions can be represented by the chemical equation A -> P, where A is the reactant and P is the product. An example of a unimolecular reaction is the decomposition of ozone (O3) to oxygen (O2) and a free radical (O): $$\ce{O3} \rightarrow \ce{O2} + \ce{O}$$.
• Bimolecular reactions involve two molecules as reactants, which collide with each other to form products. These reactions can be represented by the chemical equation A + B -> P, where A and B are reactants and P is the product. Bimolecular reactions can be further classified into two types:

1. Reactions between two molecules of the same compound (A + A -> P), such as the reaction between two NOCl molecules.
2. Reactions between two different compounds (A + B -> P), such as the reaction between CO and NO3.

In summary, unimolecular reactions involve only one reactant molecule, while bimolecular reactions involve two reactant molecules that collide with each other to form products.

Comparative Table: Unimolecular vs Bimolecular Reactions

Here is a table comparing the differences between unimolecular and bimolecular reactions:

Unimolecular reactions involve the transformation of a single molecule, while bimolecular reactions involve the collision and interaction of two molecules. In unimolecular reactions, one molecule of reactant is converted to products. On the other hand, bimolecular reactions have two reactant molecules colliding with each other, and they could be the same molecule (A + A to P) or different (A + B to P). The rate law for unimolecular reactions is Rate = k[A], where k is the rate constant and [A] is the concentration of the reactant. In contrast, bimolecular reactions follow a rate law of Rate = k[A]^2 or Rate = k[A][B], where [A] and [B] are the concentrations of the two reactants.