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Indian Forest Service (Mains)

Chemistry optional

  • 2 papers
  • 200 marks each
  • 3 h per paper

Paper I covers physical and inorganic chemistry.

Indian Forest Service (Mains), Chemistry optional · 2022 · Paper I

Q5(a). Two mechanisms of HI formation

Question

Consider two possible mechanisms for the synthesis of HI. The first is H₂ + I₂ → 2HI (rate constant k) and the second is I₂ → 2I (k₁), 2I → I₂ (k₂), 2I + H₂ → 2HI (k₃). Derive the expressions for the rate of formation of HI for both mechanisms. Under what conditions will both the mechanisms lead to the same type of kinetic equation?

Answer in brief

The direct mechanism gives d[HI]/dt = 2k[H₂][I₂]; the atomic mechanism has the same concentration dependence when k₂ ≫ k₃[H₂].

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Topic notes: Arrhenius equation, collision theory and transition-state theory, with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversH2 + I2 kineticssteady-state approximationHI formation mechanismrate lawatomic mechanism

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