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In a Finkelstein reaction, 1‑iodobutane (CH3CH2CH2CH2I) is treated with excess NaBr in dry acetone at 298 K. The standard Gibbs free energy change for the reaction is ΔG° = +5.2 kJ mol⁻¹. What is the equilibrium constant K for this reaction at 298 K?

medium MCQ 4 marks Class 12 · Chemistry · Haloalkanes and Haloarenes
  1. 0.12
  2. 1.00
  3. 3.00
  4. 12.0
Answer
0.12

The correct answer is 0.12 — Step 5: Therefore the equilibrium constant is approximately 0.12.

Step-by-step solution

  1. Step 1: Convert ΔG° to joules: 5.2 kJ mol⁻¹ = 5200 J mol⁻¹.
  2. Step 2: Use the relationship ΔG° = –RT ln K, where R = 8.314 J mol⁻¹ K⁻¹ and T = 298 K.
  3. Step 3: Rearrange to ln K = –ΔG°/(RT) = –5200/(8.314×298) = –2.098.
  4. Step 4: Exponentiate: K = e^(–2.098) ≈ 0.12.
  5. Step 5: Therefore the equilibrium constant is approximately 0.12.
Common mistake: Using ΔG° = +RT ln K instead of –RT ln K, which gives an incorrect sign

Concept tested: Calculating equilibrium constants from Gibbs free energy

Published · How this solution was prepared and checked

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