Thermodynamics
🟢 Lite — Quick Review (1h–1d)
Rapid summary for last-minute revision.
Thermodynamics — Key Facts for JEE Main • Core formula or law — write the equation: ΔQ = ΔU + ΔW (First Law: ΔU = ΔQ − ΔW) • Core concept — one sentence explanation: Heat energy supplied to a system equals the change in its internal energy plus the work done by the system on the surroundings. • Most common application of this topic: Calculating work done, efficiency of heat engines, and change in entropy for quasi-static processes. • Key numerical value or constant to memorise: Universal gas constant R = 8.314 J mol⁻¹ K⁻¹; for diatomic gases γ = Cp/Cv = 1.4 • Most tested concept in JEE Main: Work done in an isothermal reversible process: W = nRT ln(V₂/V₁) and adiabatic condition: PV^γ = constant • Common mistake students make here: Confusing signs — students often forget that when gas expands (ΔV > 0), work done by gas is positive, but from the system’s perspective W done on the system is negative. Also mixing up Cp and Cv relationships. ⚡ Exam tip: For any cyclic process, ΔU = 0, so ΔQ = ΔW. In P-V diagram area enclosed = net work done. Always check if the process is quasi-static before applying PV = nRT at every step.
🟡 Standard — Regular Study (2d–2mo)
Standard content for students with a few days to months.
Thermodynamics — JEE Main / Advanced Study Guide
Thermodynamics deals with the interconversion of heat and other forms of energy without violating the laws of thermodynamics. It describes macroscopic properties rather than microscopic behaviour.
Core Concepts and Key Equations
The Zeroth Law establishes temperature as a fundamental property — if two systems are each in thermal equilibrium with a third, they are in thermal equilibrium with each other, forming the basis of temperature measurement. The First Law of Thermodynamics is essentially the law of conservation of energy expressed as ΔQ = ΔU + ΔW, where ΔQ is heat added, ΔU is change in internal energy, and ΔW is work done by the system. For an ideal gas, ΔU = nCvΔT, independent of the process. Work done by a gas in a general quasi-static process is W = ∫PdV.
Four fundamental processes are critical:
- Isothermal (T = constant): For ideal gas, W = nRT ln(V₂/V₁), ΔU = 0, so ΔQ = ΔW
- Adiabatic (Q = 0): PV^γ = const, TV^(γ−1) = const, W = (P₁V₁ − P₂V₂)/(γ−1)
- Isochoric (V = constant): W = 0, ΔQ = ΔU
- Isobaric (P = constant): W = P(V₂ − V₁)
Mayer’s relation connects heat capacities: Cp − Cv = R, and Cp/Cv = γ. For monoatomic gas, Cv = (3/2)R, Cp = (5/2)R, γ = 5/3. For diatomic (rigid), Cv = (5/2)R, Cp = (7/2)R, γ = 1.4.
Second Law of Thermodynamics states that heat cannot spontaneously flow from a cold body to a hot body (Clausius statement) and that no heat engine can have 100% efficiency (Kelvin
📊 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 | ~7% (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
🔗 Official Resources
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