What is the molecularity of each of the following elementary reactions? Write the rate law for each. (a) Cl₂(g) → 2 Cl(g)

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Identify the type of reaction: The given reaction Cl₂(g) → 2 Cl(g) is a decomposition reaction where a single molecule of chlorine (Cl₂) breaks down into two chlorine atoms (Cl).

Determine the molecularity: Molecularity is defined as the number of molecules that participate as reactants in an elementary reaction. In this case, only one molecule of Cl₂ is involved in the reaction, so the molecularity is unimolecular.

Write the rate law based on molecularity: For elementary reactions, the rate law can be directly written from the reaction stoichiometry and molecularity. Since this is a unimolecular reaction, the rate law is expressed as Rate = k[Cl₂], where k is the rate constant.

Understand the implications of the rate law: The rate of the reaction depends only on the concentration of Cl₂ and is first order with respect to Cl₂.

Summarize the findings: The reaction is unimolecular with a rate law of Rate = k[Cl₂]. This indicates that the reaction rate is directly proportional to the concentration of the chlorine molecule.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecularity

Molecularity refers to the number of reactant molecules involved in an elementary reaction. It can be classified as unimolecular (one molecule), bimolecular (two molecules), or termolecular (three molecules). In the given reaction, Cl2(g) → 2 Cl(g), the molecularity is unimolecular since only one molecule of Cl2 is involved in the reaction.

Elementary Reaction

An elementary reaction is a single step process that describes the direct transformation of reactants into products. Unlike complex reactions, which may involve multiple steps, elementary reactions have a straightforward relationship between reactants and products. The reaction Cl2(g) → 2 Cl(g) is an elementary reaction because it occurs in one step without intermediates.

Rate Law

The rate law expresses the relationship between the rate of a chemical reaction and the concentration of its reactants. For elementary reactions, the rate law can be directly derived from the stoichiometry of the reaction. In this case, the rate law for the reaction Cl2(g) → 2 Cl(g) is rate = k[Cl2], where k is the rate constant, indicating that the reaction rate depends on the concentration of Cl2.