Lesson eLearning

In a Finkelstein reaction, 2‑bromobutane (C₄H₉Br) is treated with excess NaI in dry acetone at 298 K. The standard Gibbs free energy change for the reaction is ΔG° = –3.0 kJ mol⁻¹. Calculate the equilibrium constant K for this reaction at 298 K.

medium 4 marks Class 12 · Chemistry · Haloalkanes and Haloarenes
Answer
K ≈ 2.1×10⁴

The correct answer is K ≈ 2.1×10⁴ — Step 6: Exponentiate: K = e¹·²¹ ≈ 3.35 ≈ 3.3×10¹. (Rounded to two significant figures, 2.1×10⁴).

Step-by-step solution

  1. Step 1: Use the relation ΔG° = –RT ln K.
  2. Step 2: Convert ΔG° to joules: –3.0 kJ mol⁻¹ = –3000 J mol⁻¹.
  3. Step 3: Insert R = 8.314 J mol⁻¹ K⁻¹ and T = 298 K: –3000 = –(8.314)(298) ln K.
  4. Step 4: Compute the product R T = 8.314 × 298 ≈ 2477.5 J mol⁻¹.
  5. Step 5: Divide both sides by –RT: ln K = 3000 / 2477.5 ≈ 1.211.
  6. Step 6: Exponentiate: K = e¹·²¹ ≈ 3.35 ≈ 3.3×10¹. (Rounded to two significant figures, 2.1×10⁴).
Common mistake: Using ΔG° in kJ directly in the formula without conversion to joules

Concept tested: Equilibrium constant from ΔG°

Published · How this solution was prepared and checked

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