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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper I covers physical and inorganic chemistry.

UPSC Civil Services (Mains), Chemistry optional · 2021 · Paper I

Q6(c). Langmuir adsorption isotherm; first-order and zero-order limits

Question

Derive an equation for Langmuir's adsorption isotherm. Show that under limiting conditions of pressure, the system follows both first-order and zero-order of adsorption.

Answer in brief

θ = KP/(1 + KP) with K = ka/kd, so x/m = (x/m)max KP/(1 + KP): at low pressure x/m ∝ P¹ (first order), at high pressure x/m ∝ P⁰ (zero order).

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Topic notes: adsorption isotherms, heterogeneous catalysis and colloids, with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversLangmuir adsorption isothermmonolayer adsorptionFreundlich isothermsurface coverageBET isotherm

All parts of Question 6