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Multistep Reaction Energy Profile

A multistep reaction occurs in several elementary steps, each with its own activation energy. The energy profile helps visualize the energy changes during the reaction.

Key Concepts​

  • Elementary Steps: Individual reactions that make up the overall reaction
  • Activation Energy (Ea): Energy required to reach the transition state for each step
  • Intermediates: Species formed temporarily during the reaction
  • Transition State: High-energy state during the conversion from reactants to products
  • Rate-Determining Step (RDS): Slowest step that controls the overall reaction rate

Energy Profile Diagram​

  • Reactants → Peaks (transition states) → Intermediates → Final Products
  • The highest peak corresponds to the RDS
  • ΔH (enthalpy change) = Energy of products − Energy of reactants
    • ΔH < 0: Exothermic
    • ΔH > 0: Endothermic

Example​

A → B → C → D

  • Step 1: A → B, Ea₁ = 50 kJ/mol
  • Step 2: B → C, Ea₂ = 75 kJ/mol (RDS)
  • Step 3: C → D, Ea₃ = 30 kJ/mol
  • Overall reaction: A → D, net ΔH = −40 kJ/mol

Importance​

  • Helps understand reaction kinetics
  • Visualizes intermediate formation and energy barriers
  • Essential for designing catalysts and reaction conditions

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