| What is the First Law of Thermodynamics? | Q = ΔU + W. Heat absorbed = change in internal energy + work done by gas. All quantities in joules [ML^{2}$$T^{-2}]. |
| Sign convention for NEET? | Q > 0 (absorbed), Q < 0 (released); W > 0 (expansion), W < 0 (compression); ΔU > 0 (temperature rises). |
| What is the Zeroth Law? | If A is in thermal equilibrium with B and B with C, then A is in thermal equilibrium with C. Defines temperature. |
| What is the Second Law (Kelvin-Planck)? | No cyclic engine can convert ALL absorbed heat into work. Efficiency < 100% always. |
| What is the Second Law (Clausius)? | Heat cannot spontaneously flow from cold to hot without external work. |
| Carnot efficiency formula? | η = 1 − T2/T1, where T1 = hot reservoir (K), T2 = cold reservoir (K). Kelvin ONLY. |
| What is the COP of a refrigerator? | COP = Q2/W = T2/(T1 − T2). Can be > 1. |
| Ideal gas equation? | PV = nRT = Nk_BT. k_B = 1.38×10−2^{3} J/K. R = 8.314 J mol−1 K−1. |
| Three molecular speeds in order? | v_mp < v_avg < v_rms. Ratio = √2 : √(8/π) : √3 ≈ 1 : 1.128 : 1.224. |
| Degrees of freedom and gamma? | Monoatomic: f = 3, γ = 5/3. Diatomic: f = 5, γ = 7/5. Polyatomic: f = 6, γ = 4/3. |