$word_{count}$: 200

Thermodynamics typically contributes 1-2 questions in JEE Main (approximately 4.7% weightage). Common question types: (1) Hess's law calculation using formation or bond enthalpies — straightforward application, 2-3 minutes. (2) Spontaneity prediction — given $delta_H$ and $delta_S$, find the temperature range for spontaneity. T = $\frac{delta_H}{delta_S}$. Watch unit conversion (kJ vs J). (3) Born-Haber cycle — calculate lattice energy. Set up the cycle carefully, include all steps. (4) $delta_H$ vs $delta_U$ — count only gaseous species for $delta_{ngas}$. (5) Work calculations — know when to use -$P_{ext}$*$delta_V$ vs -nRT ln$\frac{V2}{V1}$. Common traps: mixing up kJ and J in T = $\frac{delta_H}{delta_S}$; forgetting that H2O(l) is not counted in $delta_{ngas}$; using products-reactants for bond energies (it's broken-formed); confusing $delta_G$ = 0 (equilibrium) with delta_G_{standard} = 0 (K = 1). Quick checks: exothermic + entropy increase = always spontaneous; endothermic + entropy decrease = never spontaneous. At the boiling/melting point, $delta_G$ = 0 (equilibrium between phases). Memorise: neutralisation enthalpy = -57.1 kJ/mol for strong acid-strong base.