Thermodynamics
Lite Quick Review (1h-1d)
Rapid summary.
Thermodynamics Key Facts for JEE Main
- System: Substance under study; Surroundings: Everything else
- Types: Open (mass & energy exchange), Closed (energy only), Isolated (neither)
- State Functions: U, H, S, G – path independent
- Path Functions: Q, W – depend on path taken
First Law: ΔU = Q − W; Energy can be converted but not destroyed
- Work: W = −P_ext × ΔV (expansion work)
- Heat: Q = n × C × ΔT
Key Equations:
- ΔH = ΔU + Δn_g × RT
- C_p − C_v = R
- ΔU = n × C_v × ΔT
- ΔH = n × C_p × ΔT
Hess’s Law: ΔH independent of path; use enthalpy of formation or bond enthalpies
Second Law: ΔS_universe > 0 for spontaneous processes
- ΔS_sys + ΔS_surr ≥ 0
Entropy: ΔS = q_rev/T; Disorder measure
Third Law: S° = 0 at 0 K (perfect crystal)
Gibbs Free Energy:
- ΔG = ΔH − TΔS
- ΔG < 0: Spontaneous
- ΔG = 0: Equilibrium
- ΔG > 0: Non-spontaneous
Relationships:
- ΔG° = −RT ln K
- ΔG° = −nFE°
Standard Regular Study (2d-2mo)
Standard content.
Thermodynamics JEE Main Study Guide
Thermodynamics deals with energy transformations during physical and chemical processes. The system is the portion being studied, while surroundings constitute everything else. Systems are classified as open (exchange both mass and energy), closed (energy only), or isolated (neither).
The first law establishes energy conservation: ΔU = Q − W. For constant volume processes, W = 0, so ΔU = Q_v. For constant pressure, we define enthalpy H = U + PV, making ΔH = Q_p. The relationship C_p − C_v = R holds for ideal gases.
Consider the reaction: N₂(g) + 3H₂(g) → 2NH₃(g); ΔH = −92 kJ/mol. This negative enthalpy indicates exothermic reaction releasing heat. If 2 moles form, heat released = 184 kJ.
Entropy (S) measures disorder. For the same reaction, ΔS is negative because 4 moles gaseous reactants form 2 moles gaseous products, reducing molecular randomness. However, the reaction is spontaneous at moderate temperatures because the exothermic nature (ΔH negative) drives it.
Gibbs free energy combines both factors: ΔG = ΔH − TΔS. At 298 K for ammonia synthesis with ΔH = −92 kJ and ΔS = −198 J/K, ΔG = −92,000 − (298)(−198) = −33,004 J, confirming spontaneity.
The equilibrium constant relates through ΔG° = −RT ln K. As temperature increases, the TΔS term becomes significant, potentially making ΔG positive and reversing spontaneity.
Extended Deep Study (3mo+)
Comprehensive.
Thermodynamics Comprehensive JEE Notes
Thermodynamics provides fundamental framework for predicting reaction feasibility and equilibrium positions. Understanding requires mastery of three primary laws and their interconnections.
The Zeroth Law establishes temperature as a fundamental property enabling thermal equilibrium concept. The First Law (ΔU = Q − W) establishes energy conservation, with work defined as pressure-volume work for most chemical systems: W = −∫P_ext dV. For reversible processes, W_rev = −nRT ln(V₂/V₁).
Enthalpy (H = U + PV) serves as the heat content at constant pressure. Standard enthalpy of formation (ΔH°_f) allows calculation via Hess’s law: ΔH°
📊 JEE Main Exam Essentials
| Detail | Value |
|---|---|
| Questions | 90 (30 per subject) |
| Sections | Physics, Chemistry, Mathematics |
| Type | MCQ + Numerical Value (NAT) |
| Time | 3 hours |
| Marking | +4 correct, −1 wrong (MCQ); +4 correct, 0 wrong (NAT) |
| Sessions | January + April per year; best score considered |
| Topic Weightage | ~6% (based on 2023–2025 paper analysis) |
🎯 High-Yield Topics for JEE Main
- Coordination Compounds — 8 marks
- Organic Reactions & Mechanisms — 12 marks
- Electrochemistry + Kinetics — 12 marks
- Determinants & Matrices — 10 marks
- Integration (Definite + Indefinite) — 15 marks
- Electrodynamics (Capacitance + Current) — 12 marks
📝 Previous Year Question Patterns
- Q: “Find the area bounded by the curve y = …” [2025 Math — 4 marks NAT]
- Q: “The electrons in a multi-electron atom are removed…” [2025 Chemistry — 3 marks]
- Q: “A particle of mass m is projected with velocity v at angle θ…” [2025 Physics — 4 marks]
💡 Pro Tips
- Mathematics is the highest-scoring subject for students who master it — target 100+ in Math
- In Physics, Alternating Current and EM Waves are easiest to score — rarely out of syllabus
- Organic Chemistry: questions on name reactions (Kolbe electrolysis, Hofmann, etc.) appear every year
- Coordinate Geometry: 60% of JEE Main geometry questions come from Circle + Parabola + Ellipse
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