Rate = k[A]^m[B]^n. Orders m and n are determined experimentally, NOT from stoichiometry (except for elementary reactions). Overall order = m + n. The rate constant k is specific to a reaction at a given temperature. It does NOT depend on concentration. Units of k depend on overall order n: k has units of $\frac{mol}{L}$^(1-n) $s^{-1}$. Zero order: $\frac{mol}{L.s}$. First order: $s^{-1}$. Second order: $\frac{L}{mol.s}$. Third order: L^$\frac{2}{mol^2.s}$. Higher k means faster reaction. k increases exponentially with temperature (Arrhenius equation). For complex (multi-step) reactions, the rate law is determined by the rate-determining step (slowest step).