Q7(c). Opposing first-order reactions: time to form half the equilibrium amount
The reaction cis-2-butene ⇌ trans-2-butene (k₁ forward, k₋₁ reverse) is first order in both directions. At 25 °C, the equilibrium constant is 0.406 and the forward reaction rate constant is 4.21 × 10⁻⁴ s⁻¹. Starting with a sample of pure cis isomer with [cis]₀ = 0.115 mol dm⁻³, how long will it take to form half of the equilibrium amount of the trans isomer from the cis isomer?
Answer in brief
t = ln 2/(k₁ + k₋₁) = 0.6931/1.458 × 10⁻³ s⁻¹ = 475 s (about 7.9 min).
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Coversopposing reactionsreversible first-order kineticsrelaxationcis–trans isomerisationequilibrium constant
All parts of Question 7
- 7(a) An optically active square-planar complex10 marks
- 7(b) Aqueous LaCl₃ and LuCl₃: which is more acidic10 marks
- 7(c) Opposing first-order reactions: time to form half the equilibrium amount10 marks
- 7(d) Surface area of an adsorbent from the nitrogen monolayer10 marks
- 7(e) Magnetic behaviour of copper(II) acetate and [Cu(CN)₄]³⁻10 marks