First-order half-life: $t_{1/2} = 0.693/k$ — independent of initial concentration; 75% completion $= 2 \times t_{1/2}$; 87.5% $= 3 \times t_{1/2}$.

Arrhenius two-temperature form: $\log(k_2/k_1) = (E_a/2.303R)(1/T_1 - 1/T_2)$ — always use Kelvin; slope of $\ln k$ vs $1/T$ $= -E_a/R$.

Order vs Molecularity: Order is experimental (can be 0, fractional, integer); molecularity is theoretical (positive integer 1/2/3 only; never 0 or fractional).

Catalyst effect: Lowers $E_a$ only — does not change $\Delta H$, equilibrium constant $K$, or reaction enthalpy.

Units of $k$: Zero order $= mol\,L^{-1}\,s^{-1}$; First order $= s^{-1}$; Second order $= L\,mol^{-1}\,s^{-1}$; General: $(mol\,L^{-1})^{1-n}\,s^{-1}$.