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Question #44069

Difficulty: 8/10 | 🟢 Free

The Question

The gas-phase reaction \ce{A(g) + 2B(g) <=> C(g)} has an equilibrium constant Kc=2500 M−2K_c = 2500 \text{ M}^{-2} at 600 K600 \text{ K}. The activation energy for the forward uncatalyzed reaction is 80 kJ mol−180 \text{ kJ mol}^{-1}.

To improve the rate of product formation, a solid catalyst is introduced, which alters the reaction pathway to the following mechanism: Step 1: \ce{A(g) + B(g) <=> I(g)} (Fast equilibrium) Step 2: \ce{I(g) + B(g) <=> C(g)} (Slow, rate-determining step)

The catalyst lowers the activation energy of the forward reaction by 11.5 kJ mol−111.5 \text{ kJ mol}^{-1}. Assuming ideal gas behavior and that the concentration of the intermediate \ce{I(g)} is negligible at macroscopic equilibrium, what is the value of the equilibrium constant KpK_p for the catalyzed reaction at 600 K600 \text{ K}?

(Given: R≈112 L bar K−1 mol−1R \approx \frac{1}{12} \text{ L bar K}^{-1} \text{ mol}^{-1} for pressure calculations, R=8.314 J K−1 mol−1R = 8.314 \text{ J K}^{-1} \text{ mol}^{-1} for energy calculations, and e2.3≈10e^{2.3} \approx 10)

Options

  • A.

    1 bar−21 \text{ bar}^{-2}

  • B.

    10 bar−210 \text{ bar}^{-2}

  • C.

    50 bar−150 \text{ bar}^{-1}

  • D.

    500 bar−1500 \text{ bar}^{-1}

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Relationship between Kp and Kc|Reaction Progress Coordinate

Why This Question Is Tricky

Common Mistakes

This problem tests the student's ability to distinguish between kinetic parameters (which change with mechanism) and thermodynamic parameters (which remain invariant).

The primary trap is the assumption that a catalyst, by lowering the activation energy or altering the reaction mechanism, changes the equilibrium constant.

Students often erroneously adjust KcK_c using the Arrhenius factor eΔEa/RTe^{\Delta E_a / RT} (Option B), forgetting that the backward activation energy is lowered equally.

Additionally, the problem presents a multi-step mechanism to bait students into using the Δng\Delta n_g of the rate-determining step (Option C) rather than the overall macroscopic stoichiometry required for the Kp/KcK_p/K_c relationship.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterEquilibrium - Class 11 Part 1
ConceptRelationship between Kp and Kc
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree