First Law: Q = $\Delta U$ + W. Process zero: isothermal → $\Delta U$ = 0; adiabatic → Q = 0; isochoric → W = 0; isobaric → nothing zero.

Carnot efficiency: η = 1 − $T_{2}$/$T_{1}$ (kelvin only!). COP_refrigerator = $T_{2}$/($T_{1}$ − $T_{2}$). η < 1 always; COP can exceed 1.

Molecular speeds (ascending): v_mp < v_avg < v_rms. Formulas: √(2RT/M) : √(8RT/πM) : √(3RT/M). Ratio ≈ 1 : 1.128 : 1.224.

Gas DOF and γ: Monoatomic f = 3, γ = 5/3. Diatomic f = 5, γ = 7/5. Polyatomic f = 6, γ = 4/3. U = (f/2)nRT.

NEET golden rules: Always convert °C to K for Carnot. Adiabatic ≠ isothermal (Q = 0 ≠ $\Delta T$ = 0). Adiabatic curve is steeper than isothermal on PV diagram. v_mp is smallest, v_rms is largest.