JEE Main Thermodynamics: Physics + Chemistry Complete Guide
Thermodynamics appears in both Physics and Chemistry in JEE Main — making it a chapter where double preparation pays off. Here is a unified guide covering both Physics and Chemistry thermodynamics.
Physics Thermodynamics (2-3 questions)
Zeroth, First, and Second Laws. Isothermal, adiabatic, isochoric, isobaric processes and their PV diagrams. Carnot engine efficiency = 1 - T_cold/T_hot. Entropy statement of Second Law. JEE Main: area under PV diagram = work done.
Kinetic Theory of Gases
Often tested with Thermodynamics. Key: average, rms, most probable speeds. Degrees of freedom, equipartition theorem (energy = f/2 × kT per molecule). Real vs ideal gas behavior. van der Waals equation.
Chemistry Thermodynamics (2-3 questions)
Hess's Law for enthalpy calculations. Bond enthalpies for ΔH of reaction. Gibbs free energy: ΔG = ΔH - TΔS. Spontaneity conditions (ΔG < 0). Relationship between ΔG° and equilibrium constant Kp.
Entropy and Spontaneity
JEE Main tests: Given ΔH and ΔS, find temperature above/below which reaction is spontaneous. This is a direct application of ΔG = ΔH - TΔS = 0. Also: entropy change for phase transitions (melting, vaporization).
High-Yield Formulas to Memorize
Physics: η(Carnot) = 1 - T₂/T₁, ΔU = nCvΔT (always), W = P(V₂-V₁) for isobaric. Chemistry: ΔG° = -RT ln K, ΔG = ΔG° + RT ln Q, ΔH_rxn = Σ(bond energies broken) - Σ(bond energies formed).
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