In heterogeneous catalysis (solid catalyst with reactants in a different phase), which statement best describes what happens to activation requirements and the catalyst's state after reaction completion?

Introduction / Context:
Heterogeneous catalysis is central to chemical engineering, where a solid catalyst accelerates reactions of gas or liquid reactants. This question checks your understanding of what a catalyst actually does to activation requirements and what happens to the catalyst after the reaction cycle.

Given Data / Assumptions:

• Reactants and catalyst are in different phases.
• We consider standard catalytic cycles where adsorption and desorption occur.
• No catalyst poisoning or deactivation is assumed.

Concept / Approach:
A catalyst provides an alternative pathway with a lower activation free energy (ΔG‡). It increases the rate constant k without changing the reaction's equilibrium position (ΔG° remains unchanged). In heterogeneous catalysis, surface adsorption and formation of surface intermediates are typical.

Step-by-Step Solution:
1) Rate constant relation: k = A * exp(-ΔG‡ / (R*T)). Lower ΔG‡ increases k at the same T.2) A catalyst alters ΔG‡ but does not alter ΔG°; hence equilibrium composition is unchanged.3) In heterogeneous catalysis, reactants adsorb to the surface, form intermediates, react, then products desorb; the catalyst is regenerated.4) Because the catalyst is regenerated, it is not consumed; small amounts can process large throughput but rate still depends on available active sites (i.e., catalyst amount and surface area matter).

Verification / Alternative check:
If a catalyst changed ΔG° (standard Gibbs energy of reaction), the equilibrium constant K would change. Practically, catalysts speed up reaching equilibrium but do not alter the equilibrium composition—confirming the correct view.

Why Other Options Are Wrong:
Option b: Catalyst loading and surface area influence rate; saying concentration never matters is incorrect.
Option c: Surface intermediates and adsorption are routine in heterogeneous catalysis.
Option d: Surface area, dispersion, and active sites are crucial in practice.
Option e: A catalyst does not change ΔG°; equilibrium is unchanged.

Common Pitfalls:
Confusing rate acceleration (kinetics) with equilibrium shift (thermodynamics), and assuming catalysts are “used up.”

Final Answer:
The free energy barrier is lowered and the catalyst is recovered unchanged.