Ea = R × ln(k2/k1) / (1/T1 - 1/T2)
Activation energy (Ea) is the minimum energy required for reactant molecules to undergo a chemical reaction. The Arrhenius equation k = A × e^(-Ea/RT) relates the rate constant to temperature. By measuring k at two temperatures, Ea can be calculated: Ea = R × ln(k2/k1) / (1/T1 - 1/T2). R is the gas constant (8.314 J/mol·K). Typical Ea values range from 40-200 kJ/mol. Catalysts work by lowering Ea, providing an alternative reaction pathway. Enzymes in biological systems lower Ea dramatically — often by 50-70%, increasing reaction rates by factors of 10^6 to 10^12.