Lecture9 - Pre-equilibrium approximation Product formed...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Physical Chemistry Lecture 9 Kinetics of enzymatic reactions Biological reactions Usually occur in aqueous solution Generally multiple-step reactions Can be grouped in classes of reactions that happen by similar mechanisms Enzyme catalysis Photochemically initiated reactions Electron transfer Pre-equilibrium approximation A simple model Assumes the existence of a reactive intermediate Requires a difference in time scale of the elementary processes Fast establishment of equilibrium Slower transformation of intermediate into product Requires a difference in activation energies of the steps slower P I fast B A I fast I B A p r f k k k  Pre-equilibrium approximation Product formed only by second step Elementary rate determined by intermediate’s concentration Assumption of rapid equilibrium Gives the intermediate’s concentration in terms of reactant concentrations Substitution gives an expression for the rate in terms of reactant concentrations Effective rate constant depends on all three rates Effective activation energy depends on all elementary activation energies Example: formation of NO 2 from NO and O 2 slower P I fast B A I fast I B A p r f k k k ] ][ [ ] [ ] ][ [ ] [ ] ][ [ ] [ ] [ ] [ 2 B A k K dt P d B A K I B A I k k K I k dt P d p eq eq r f eq Catalytic action Some reactions proceed with the presence of material that are not Reactants Products Intermediates in the sense of our definition Materials that affect a reaction, but are not among the reactants or products, are Catalysts if they promote a reaction Inhibitors if they slow or stop a reaction
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/02/2012 for the course CHEM 419 taught by Professor Staff during the Fall '10 term at University of Delaware.

Page1 / 3

Lecture9 - Pre-equilibrium approximation Product formed...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online