The heterogeneous catalytic reaction A(g) + B(g) → C(g) proceeds according to the rate expression -rA = k·KA·pA·PB / (1 + KA·PA + Kc·pc). What represents the rate-controlling step for this mechanism_______________?
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Answer: C. Surface reaction between absorbed A and B in the gas phase
Explanation
When a gas phase species reacts directly with an adsorbed species, unadsorbed pressure terms appear in the rate numerator. Langmuir Hinshelwood mechanisms derive these specific surface reaction rate expressions based on adsorption steps. The presence of gas phase reactant pressure in the numerator confirms surface reaction between adsorbed and gas species. Heterogeneous catalytic mechanisms include Eley Rideal pathways where gas phase molecules react with adsorbed species. Surface reaction rate equations depend heavily on which elementary step controls the overall process speed. Adsorption equilibrium constants quantify surface coverage fractions for participating reactants and products.
Industrial catalytic hydrogenation reactions frequently involve complex dual path or Eley Rideal kinetic mechanisms. Understanding specific surface mechanisms helps chemical engineers optimize catalytic reactor operating pressures. Reactor simulation software relies on detailed Langmuir Hinshelwood rate expressions for accurate predictions. Option A suggests absorption control, which yields different denominator and numerator dependencies. Option B describes dual site surface reaction between two adsorbed species, featuring only adsorbed terms. Option D reverses the adsorbed and gas phase roles, which would alter the mathematical structure of the rate law.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
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