Indian Forest Service (Mains)
Chemistry optional
- 2 papers
- 200 marks each
- 3 h per paper
Paper I covers physical and inorganic chemistry.
Thermodynamics and statistical thermodynamics: every question, 2021 to 2025
17 parts worth 163 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.
Thermodynamic systems, states and processes, work, heat and internal energy; first law of thermodynamics, work done on the systems and heat absorbed in different types of processes; calorimetry, energy and enthalpy changes in various processes and their temperature dependence. Second law of thermodynamics; entropy as a state function, entropy changes in various processes, entropy–reversibility and irreversibility, free energy functions; criteria for equilibrium, relation between equilibrium constant and thermodynamic quantities; Nernst heat theorem and third law of thermodynamics. Micro and macro states; canonical ensemble and canonical partition function; electronic, rotational and vibrational partition functions and thermodynamic quantities; chemical equilibrium in ideal gas reactions.
Notes: Second and third laws: entropy, Gibbs and Helmholtz energies, Maxwell relations (full notes) · short notes
Notes: Chemical potential, partial molar quantities, Gibbs–Duhem equation, fugacity and activity (full notes) · short notes
Notes: Chemical equilibrium: ΔG° and K, Kp, Kc and Kx, van ’t Hoff isochore and isobar (full notes) · short notes
Notes: First law of thermodynamics: work, heat, enthalpy, adiabatic changes, Joule–Thomson effect, thermochemistry (full notes) · short notes
Notes: Statistical thermodynamics: Boltzmann distribution, partition functions, Sackur–Tetrode equation (full notes) · short notes
2025
- Q1(c) Formation free energy of uranium hydride8 marks Answered
- Q1(d) Pressure dependence of solid Gibbs energy8 marks Answered
- Q3(b)(ii) Entropy change along two paths10 marks Answered
- Q3(c) Three-state nuclear-spin partition function10 marks Answered
2024
- Q1(b) Entropy of water-vapour formation at 373 K8 marks Answered
- Q3(b) Heat capacity of an Einstein crystal10 marks Question only
- Q8(c) Entropy comparison of neon and argon10 marks Answered
2023
- Q1(d) Derivatives of thermodynamic potentials8 marks Answered
- Q3(d) Pressure as a state function10 marks Question only
- Q4(a) Translational entropy of nitrogen10 marks Answered
2022
- Q1(d) Neutral pH at body temperature8 marks Answered
- Q3(b)(i) Adiabatic mixing of ice and hot water10 marks Question only
- Q3(b)(ii) Trouton rule5 marks Question only
- Q4(b) Rotational partition function15 marks Answered
2021
- Q1(b) Changing the enthalpy reference8 marks Answered
- Q3(b) Temperature and decomposition of silver oxide15 marks Question only
- Q4(b) Canonical partition function and heat capacity10 marks Answered
