Unimolecular reaction

A unimolecular reaction refers to a reaction that occurs in a single step. It involves the decomposition or rearrangement of a single molecule. This type of reaction is also known as an elementary reaction because it is the simplest representation of a chemical reaction.

Key Points:
1. Definition: A unimolecular reaction is a reaction that occurs in a single step and involves the decomposition or rearrangement of a single molecule.
2. Elementary reaction: Unimolecular reactions are also known as elementary reactions because they represent the simplest form of a chemical reaction.
3. Rate: The rate of a unimolecular reaction is determined solely by the concentration of the reactant molecule and follows first-order kinetics.
4. Energy profile: The energy profile of a unimolecular reaction typically consists of a single transition state and does not involve the collision of multiple molecules.
5. Examples: Examples of unimolecular reactions include the decomposition of unstable molecules, such as the isomerization of cyclopropane to propene and the dissociation of molecular chlorine into chlorine radicals.
6. Reaction rate: Since unimolecular reactions occur in a single step, the reaction rate is determined solely by the concentration of the reactant molecule. The rate equation for a unimolecular reaction is given by the equation: rate = k[A], where [A] represents the concentration of the reactant molecule and k is the rate constant.
7. Catalysts: Unimolecular reactions can be influenced by the presence of catalysts, which can increase the rate of the reaction by providing an alternative reaction pathway with a lower activation energy.

In summary, a unimolecular reaction is a reaction that occurs in a single step and involves the decomposition or rearrangement of a single molecule. It is the simplest representation of a chemical reaction and follows first-order kinetics.