k = A × e^(-Ea/RT)
Proposed by Svante Arrhenius in 1889, k = A × e^(-Ea/RT) describes how reaction rates depend on temperature. A (the pre-exponential factor) represents the frequency of molecular collisions with correct orientation — typically 10^10 to 10^13 s⁻¹. Ea is the activation energy barrier. R = 8.314 J/mol·K. A 10°C temperature increase typically doubles the reaction rate (for Ea ≈ 50-75 kJ/mol). An Arrhenius plot (ln k vs 1/T) gives a straight line with slope = -Ea/R, allowing graphical determination of Ea. The equation explains why refrigeration preserves food (lower T → exponentially slower bacterial reactions) and why enzymes are so effective (they lower Ea without changing T).