Indian Forest Service (Mains)
Chemistry optional
- 2 papers
- 200 marks each
- 3 h per paper
Paper I covers physical and inorganic chemistry.
Chemical kinetics: every question, 2021 to 2025
12 parts worth 122 marks have been set on this unit in UPSC IFoS Chemistry Paper I from 2021 to 2025. Each one opens on its own page with the question, the answer in brief and the key points.
Concentration dependence of rate of reaction; differential and integral rate equations for zeroth, first, second and fractional order reactions. Rate equations involving reverse, parallel, consecutive and chain reactions; effect of temperature and pressure on rate constant. Study of fast reactions by stop-flow and relaxation methods. Collisions and transition state theories.
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
- Q5(a) Order from total-pressure measurements8 marks Answered
- Q6(a)(i) Ozone decomposition10 marks Answered
- Q6(b)(i) Arrhenius temperature from half-life10 marks Answered
2024
- Q2(c) Arrhenius parameters from a logarithmic law10 marks Answered
- Q3(a) Thermodynamic transition-state theory15 marks Question only
2023
- Q5(a) Integration of a reversible first-order reaction8 marks Answered
- Q6(a) Initial-rate analysis15 marks Answered
2022
- Q5(a) Two mechanisms of HI formation8 marks Answered
- Q8(c)(i) Equilibrium and relaxation of an isomerisation10 marks Question only
- Q8(c)(ii) Zero or negative activation energy5 marks Question only
2021
- Q5(a) Second-order conversion after 60 minutes8 marks Answered
- Q6(a) Reversible first-order reaction15 marks Answered
UPSC Indian Forest Service (Main) Chemistry Paper I: Model Answers 2021 to 2025
- All eight questions of each paper, with the question printed above its answer
- Physical chemistry numericals worked with units; inorganic structures drawn
- Topic-wise weightage and a topic-wise index