Which of the following best defines an elementary reaction in chemical kinetics?

• A. A reaction that occurs in a single step and whose rate law can be written directly from its molecularity.
• B. A reaction that reaches equilibrium rapidly.
• C. A reaction that involves multiple steps and intermediates.
• D. A reaction whose rate depends only on the concentration of the products.

Answer: (A)

Verified step by step guidance

1. Understand that an elementary reaction is a single-step process in a chemical reaction mechanism, meaning it occurs in one molecular event without any intermediates.
2. Recall that the rate law for an elementary reaction can be directly written from its molecularity, which is the number of reactant molecules involved in that single step.
3. Recognize that reactions involving multiple steps and intermediates are called complex or overall reactions, not elementary reactions.
4. Note that the rate law of an elementary reaction depends on the concentration of reactants, not products, and it reflects the molecularity of the step.
5. Conclude that the best definition of an elementary reaction is: a reaction that occurs in a single step and whose rate law can be written directly from its molecularity.