The rate controlling step for the heterogeneous irreversible catalytic reaction A(g) + B(g) → C(g) is the surface reaction of absorbed A with absorbed B to give adsorbed C. The rate expression for this reaction can then be written as (where, KA, KB and KC are the equilibrium constants and is the rate constant of the rate controlling step) ?

Correct answer: D. k KAKB pApB / (1 + KApA + KBpB + KCpC)2

  • A. k KA pApB / (1 + KApA + KBpB)
  • B. k KAKB pApB / (1 + KApA + KBpB)
  • C. k KAKB pApB / (1 + KApA + KBpB + KCpC)
  • D. k KAKB pApB / (1 + KApA + KBpB + KCpC)2

Explanation

With competitive adsorption, the surface coverages of adsorbed A and B are proportional to K_Ap_A and K_Bp_B, while the vacant-site denominator is 1 + K_Ap_A + K_Bp_B + K_Cp_C. Since the surface reaction requires both adsorbed A and B, the denominator is squared.

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