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Steady-State Approximation

The steady-state approximation is a method used in chemical kinetics to simplify the analysis of complex reaction mechanisms.

Key Concepts​

  • Intermediate Species: Short-lived species formed in a reaction mechanism
  • Steady-State Assumption: The concentration of the intermediate remains approximately constant during most of the reaction
    • Rate of formation ≈ Rate of consumption

Applying the Steady-State Approximation​

  1. Identify intermediate species in the mechanism
  2. Write rate expressions for formation and consumption of the intermediate
  3. Set the net rate of change of the intermediate to zero
  4. Solve for intermediate concentration
  5. Substitute into the overall rate law

Example​

For the reaction: A → B → C

  • B is an intermediate: d[B]/dt ≈ 0
  • Steady-state approximation allows simplification of rate expressions to focus on A → C

Importance​

  • Simplifies mathematical treatment of multistep reactions
  • Helps derive rate laws for complex mechanisms
  • Widely used in enzymatic reactions and catalytic cycles

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