(b) What is the difference between a unimolecular and a bimolecular elementary reaction?

Verified step by step guidance

1. Understand that an elementary reaction is a single step reaction with a specific molecularity, which refers to the number of reactant molecules involved in the reaction.
2. A unimolecular reaction involves a single reactant molecule undergoing a transformation to form products. An example is the decomposition of a single molecule, such as the isomerization of cyclopropane to propene.
3. A bimolecular reaction involves two reactant molecules colliding and reacting to form products. An example is the reaction between two molecules of hydrogen gas and one molecule of oxygen gas to form water.
4. Recognize that the molecularity of a reaction is determined by the number of molecules that come together to react in an elementary step, and it is always a whole number.
5. Note that the rate law for an elementary reaction can be directly written from its molecularity: unimolecular reactions have a first-order rate law, while bimolecular reactions have a second-order rate law.

Key Concepts

Elementary Reactions

Elementary reactions are the simplest types of chemical reactions that occur in a single step, involving a direct interaction between reactants. They are characterized by their molecularity, which indicates the number of reactant molecules involved in the reaction. Understanding elementary reactions is crucial for analyzing reaction mechanisms and kinetics.

Unimolecular Reactions

Unimolecular reactions involve a single reactant molecule that undergoes a transformation to form products. This type of reaction typically follows first-order kinetics, where the rate of reaction depends solely on the concentration of the single reactant. An example is the isomerization of a molecule, where one molecule rearranges to form another without the involvement of other reactants.

Bimolecular Reactions

Bimolecular reactions involve two reactant molecules that collide and react to form products. These reactions can be either two molecules of the same species or two different species. Bimolecular reactions generally follow second-order kinetics, where the rate of reaction depends on the concentrations of both reactants. An example is the reaction between two different gases to form a product.