Which theoretical framework most directly explains the mechanism of catalysis and the associated rate enhancement?

Introduction / Context:
Catalysis accelerates reactions by lowering the free energy of activation. Understanding which theoretical framework best captures this mechanism is crucial for reaction engineering and kinetics interpretation.

Given Data / Assumptions:

• We compare different theories: activated complex theory, collision theory, and thermodynamics.
• We focus on mechanistic explanation of rate enhancement.

Concept / Approach:
Activated complex theory (transition state theory) posits that reactants pass through an activated complex with free energy ΔG‡. Catalysts provide an alternate pathway with a lower ΔG‡, raising k via k = (kB*T/h)exp(-ΔG‡/(RT)). Collision theory addresses frequency and energy of collisions but lacks a robust transition state formalism for catalysis. Thermodynamics defines equilibrium, not rates.

Step-by-Step Solution:
1) Identify the need: a model relating rate to an energy barrier and how catalysts change that barrier.2) Activated complex theory provides a quantitative expression linking rate constant and ΔG‡.3) A catalyst lowers ΔG‡ for the alternative pathway, increasing k at the same temperature.4) Collision theory cannot by itself describe surface intermediates or modified transition states.

Verification / Alternative check:
Empirical observation: catalysts change rate constants without changing equilibrium constants. This matches a lowered ΔG‡ picture from transition state theory, not pure thermodynamics.

Why Other Options Are Wrong:
Option b: Collision theory is qualitative for gas-phase collisions and does not capture catalytic pathways in detail.
Option c: Thermodynamics sets equilibrium, not kinetics.
Option d: Not applicable because a well-established framework exists.
Option e: Modern view incorporates a transition state; an “intermediate-only” view is incomplete.

Common Pitfalls:
Confusing equilibrium (thermodynamics) with rate (kinetics) and overlooking the role of ΔG‡.

Final Answer:
Activated complex (transition state) theory.