Steady-state and pre-equilibrium kinetic approximations
A low-concentration intermediate can have approximately equal formation and consumption rates after a short transient, allowing its rate equation to be eliminated from a mechanism.
Key knowledge
A low-concentration intermediate can have approximately equal formation and consumption rates after a short transient, allowing its rate equation to be eliminated from a mechanism. A pre-equilibrium approximation instead assumes a fast reversible step maintains its equilibrium ratio before slower conversion. These assumptions are distinct and require compatible timescales.
Conditions and scope
- Test the assumed timescale separation and concentration regime; neither approximation applies to every elementary sequence.
- Agreement with an overall rate law does not uniquely prove a mechanism.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
- Chemistry 2e, 12.6 Reaction MechanismsPaul Flowers, Klaus Theopold, Richard Langley and William R. Robinson — OpenStax, Rice UniversityTextbook chapter
- Lectures 7–8: Enzyme Kinetics and Inhibition, pp. 2–5 and 10–12John Essigmann, Joanne Stubbe and Bogdan Fedeles — MIT OpenCourseWare, Biological Chemistry I (Fall 2013)Textbook chapter · PDF
Evidence and review
Read MIT enzyme derivation pp. 2–5: quasi-steady formation/consumption and the separate k−1≫k2 limit giving an equilibrium dissociation constant; OpenStax supplies elementary/rate-limiting context.
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Entry details
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- uni-chem-steady-state-intermediate
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- core.1
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- University core expansion