UPSC Combined Geo-Scientist
Chemist
- 3 descriptive papers
- 200 marks each
- 3 h per paper
Mains Paper II covers physical chemistry.
Chemical kinetics and catalysis: every question, 2016 to 2025
56 parts worth 386 marks have been set on this unit in UPSC Geo-Scientist Chemistry Mains Paper II from 2016 to 2025. Each one opens on its own page with the question, the answer in brief and the key points.
Second order reactions. Determination of order of reactions. Parallel and consecutive reactions. Temperature dependence of reaction rate, energy of activation. Collision theory and transition state theory of reaction rates. Enthalpy of activation, entropy of activation, effect of dielectric constant and ionic strength on reaction rate, kinetic isotope effect. Physisorption and chemisorption, adsorption isotherms, Freundlich and Langmuir adsorption isotherms, BET equation, surface area determination; colloids, electrical double layer and colloid stability, electrokinetic phenomenon. Elementary ideas about soaps and detergents, micelles, emulsions.
Notes: Adsorption, heterogeneous catalysis and colloids (full notes) · short notes
Notes: Theories of reaction rate: Arrhenius, collision and transition-state theory (full notes) · short notes
Notes: Rate laws and order: integrated rate equations, half-life, reversible, parallel and consecutive reactions (full notes) · short notes
2025
- Q1(g) Overall equation and the role of each species5 marks Answered
- Q1(h) log k against pH for specific H⁺ catalysis5 marks Answered
- Q6 Surface area of a catalyst from a nitrogen monolayer10 marks Answered
- Q12(a) t₀.₇₅ = 3 t₀.₅ for a second-order reaction5 marks Answered
- Q12(b) Orders in sucrose and H⁺ from half-lives10 marks Answered
- Q12(c) Pressures for a given coverage on a Langmuir surface5 marks Answered
2024
- Q1(g) Rate constant in dm³ mol⁻¹ s⁻¹5 marks Answered
- Q1(h) BET equation and its terms5 marks Answered
- Q5(a) Order of a gas decomposition from two rates5 marks Answered
- Q5(b) Temperature and adsorption; detergent and surface tension5 marks Answered
- Q7(a) Assumptions of the Langmuir adsorption isotherm5 marks Question only
- Q11(a) Time for 99 % and 99.9 % completion of a first-order reaction10 marks Question only
- Q11(b) Activation energy from the slope of an Arrhenius plot5 marks Question only
2023
- Q1(g) Activation energy of 2HI → H₂ + I₂5 marks Answered
- Q1(h) Best coagulant for the Sb₂S₃ sol5 marks Answered
- Q5 Enthalpy and entropy of activation from the Arrhenius parameters10 marks Question only
- Q9(a) Half-life method for the order of reaction2 marks Question only
- Q9(b) Primary salt effect for persulfate and iodide2 marks Question only
- Q9(c) Entropy change on adsorption2 marks Question only
- Q13(a) Consecutive first-order reactions: [A], [B] and [C] against time15 marks Answered
- Q13(b) Time at which [B] is a maximum5 marks Answered
2022
- Q1(g) Half-life of a second-order reaction5 marks Answered
- Q1(h) Brownian movement and Tyndall effect: why only colloids5 marks Answered
- Q5 Ionic strength and the rate constant: primary salt effect10 marks Question only
- Q13(a) Parallel (side) reactions: rate equation and k₁, k₂10 marks Answered
- Q14(a) BET equation and the surface area of a powdered catalyst10 marks Question only
2021
- Q1(g) Why a finely powdered adsorbent works better5 marks Answered
- Q1(h) Half-life of a first order reaction5 marks Answered
- Q5 Collision theory of bimolecular gas reactions10 marks Question only
- Q12(b) Activation energy of N₂O₅ decomposition from A and k10 marks Answered
2020
- Q1(g) Reaction order and rate constant5 marks Answered
- Q1(h) Catalytic rate enhancement5 marks Answered
- Q5 Opposing first-order reactions10 marks Answered
- Q6(a) Molar conductivity of a surfactant solution with concentration5 marks Question only
- Q6(b) Added NaCl lowers the CMC of SDS5 marks Question only
- Q13(a) Unequal-concentration second-order kinetics10 marks Answered
- Q13(b) Numerical second-order rate constant10 marks Answered
2019
- Q1(j) Zero-order half-life5 marks Answered
- Q1(k) Physical and chemical adsorption5 marks Answered
- Q8(a) Adsorption isotherm and gas volume5 marks Answered
- Q14 Consecutive reactions A → B → C20 marks Question only
2018
- Q1(j) Primary kinetic salt effect5 marks Answered
- Q1(k) Heat of spontaneous adsorption5 marks Answered
- Q6(a) Second-order half-life5 marks Answered
- Q6(b) Time for HI pressure decrease5 marks Answered
- Q8(b) Langmuir constant from adsorption data5 marks Answered
- Q14(c) Half-life of a second-order reaction5 marks Question only
2017
- Q1(f) Zero-order integrated law6 marks Answered
- Q8(a) Time for 99.9 percent completion5 marks Answered
- Q14(a) Langmuir isotherm for dissociative adsorption of O₂10 marks Question only
- Q15(c) Arrhenius equation units4 marks Answered
2016
- Q1(i) Rate-law determination5 marks Answered
- Q1(j) Monolayer surface area5 marks Answered
- Q5 Parallel first-order reactions10 marks Answered
- Q6 Dissociative Langmuir adsorption10 marks Answered
- Q11 Zeta potential: significance and measurement20 marks Question only
UPSC Combined Geo-Scientist (Main) Chemistry Paper II: Model Answers 2021 to 2025
- All fifteen questions of each paper, with the question printed above its answer
- Numericals worked from formula to result with units; graphs with labelled axes
- Topic-wise weightage and a topic-wise index