Elementary Reactions and Mechanisms Quiz

Elementary Reactions

• An elementary reaction is a single-step reaction characterized by a single transition state, lacking intermediates.
• Unimolecular reactions involve one species transforming into products; an example includes O2 decomposing into O3.
• Bimolecular reactions involve two species reacting; examples include O2 and another reactant yielding products.

Reaction Mechanisms

• A reaction mechanism outlines the step-by-step sequence of elementary reactions leading to an overall chemical change.
• The molecularity of a reaction refers to the number of molecules involved in an elementary reaction step.
• Unimolecular: represented as A → products; Bimolecular: represented as A + B → products or 2A → products.

Termolecular Reactions

• Termolecular reactions involve three molecules colliding simultaneously, making them rare due to the low probability of correct orientation and collision.
• When they do occur, termolecular reactions are typically slow.

Rate Laws and Mechanisms

• The reaction 2 NO(g) + Cl2(g) → 2 NOCl(g) follows the rate law: rate = k[NO]²[Cl2].
• A proposed mechanism includes two steps: NO + Cl2 → NOCl2 and NOCl2 + NO → 2 NOCl.
• If the first step is rate-determining, the rate law would be based solely on its reactants.
• The observed rate law indicates that the proposed mechanism aligns with experimental data, confirming the participation of the specified reactants.