VKC ScienceChemistry for written exams Telegram

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 · 2025 · Paper I

Q6(c). Langmuir adsorption isotherm

Question

Mentioning the requisite assumptions, derive the equation of the Langmuir adsorption isotherm. Show that the Langmuir isotherm holds at low pressure but fails at high pressure.

Answer in brief

θ = Kp/(1 + Kp) with K = ka/kd; at low pressure θ = Kp, as observed, while at high pressure it predicts a constant monolayer though real adsorption goes on rising.

Part of VKC Basic

Read the key points and the full model answer with VKC Basic

VKC Basic (₹999 for 6 months) opens every solved answer, the notes, the handbook and the daily answer archive. Every Mains test series includes it.

See what is included Already a member? Sign in

The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

The handwritten model answer pages open with the VKC plan.
Read the whole 2025 solution2025 question paper

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

CoversLangmuir adsorption isothermmonolayer adsorptionsurface coverageBET isothermchemisorption

All parts of Question 6