During a classroom demonstration the instructor places a catalyst pellet into a sealed flask containing the equilibrium mixture
CO (g) + H_2O (g) ⇌ CO_2 (g) + H_2 (g)
The colourless gases make visual observation difficult, so the instructor connects the flask to a pressure sensor that records the total pressure over time at constant temperature and volume. The sensor trace shows a rapid change in pressure immediately after the catalyst is introduced, followed by a plateau identical to the original equilibrium pressure.
A group of students concludes that the catalyst must have shifted the equilibrium to the right because the pressure changed. Another group argues that equilibrium was unaffected.
Respond to the prompts below, providing a coherent, structured argument.
(a) Explain, at the molecular level, why the total pressure in the flask changes immediately upon addition of the catalyst even though temperature and volume are constant.
(b) Construct a logical rebuttal to the claim that "the catalyst shifted the equilibrium position." Your answer must reference both kinetic and thermodynamic considerations.
(c) Propose a follow-up experiment (other than monitoring total pressure) that would allow the class to decide conclusively whether the catalyst altered the equilibrium position. Outline the data you would expect for both scenarios: catalyst affects equilibrium vs. catalyst affects only rate.
(d) Reflect on common misconceptions about catalysts in equilibrium systems. Identify two such misconceptions and correct each with precise chemical reasoning.