Activated Complex Theory and Transition State Theory are often considered synonymous, as both describe the same fundamental concept in chemical kinetics. The activated complex is a transient arrangement of atoms that occurs at the transition state during a reaction. While some argue they are interchangeable, others emphasize subtle distinctions in their applications and interpretations. The activated complex represents the highest energy state along the reaction pathway, which is crucial for understanding reaction mechanisms. Ultimately, both theories provide insights into the energy changes and molecular interactions during chemical reactions.