The Arrhenius equation & activation energy
Activation energy (Ea) is the minimum energy required for a reaction to occur. The Arrhenius equation relates rate constants to temperature:
k = A · e^(−Ea / RT)
Using two rate constants at two temperatures, Ea can be found with:
Ea = R · ln(k₂/k₁) / (1/T₁ − 1/T₂)
Effect of activation energy
- Low Ea (<40 kJ/mol): Very fast reactions (radical reactions, enzyme-catalyzed)
- Medium Ea (40–150 kJ/mol): Typical organic reactions
- High Ea (>150 kJ/mol): Very slow reactions at room temperature
Catalysts work by lowering the activation energy, providing an alternative reaction pathway.