kinetics

kinetics - Introduction to reaction kinetics Lingchong You...

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Introduction to reaction kinetics Lingchong You
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Thermodynamics is the study and understanding of whether a process can occur, regardless how long it takes. •The 2 nd law dS isolated > 0 (or dS sys + dS surrondings >0) for spontaneous processes • At constant T, P (as true for many chemical reactions) dG < 0 for spontaneous processes Kinetics is the study of how fast things happen. Concepts of this lecture: • Simple chemical kinetics • Relaxation methods
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For example ADP + P i ATP + H 2 O ATPase ADP + P i ATP + H 2 O (1) 0' 31 / Gk J m o l ∆= (2) • The difference between the reactions is the rate! The rate is determined by (a) the mechanisms of reactions. (b) other factors. e.g., solution buffer, the concentration of ATPase, the activitiy of ATPase, and the type of ATPase. ATP + H2O ADP + Pi -ATPase +ATPase • Virtually all metabolic reactions are too slow to support the life in the absence of enzymes. • Further, enzymes provide a way to control biological processes, so that they proceed at appropriate rates and under appropriate conditions
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Key elements in kinetic analysis of chemical reactions stoichiometry: how many molecules of each reactant are converted to how many molecules of each product? rate of chemical reactions : how fast? conservations of mass and energy.
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Types of reactions Most reactions are complex reactions which involve multiple steps elementary reactions . Each elementary reaction occurs through direct interactions between reactants. Example: enzymatic conversion of substrate (S) to product (P) S+ E Æ P + E often consists of two elementary steps: 1. S + E ¤ ES 2. ES Æ P +E Irreversible reaction: A Æ B Reversible reaction: A B
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I. Rate of chemical reactions Reaction rate R rate of concentration change divided by the stoichiometric coefficient in the balanced chemical reaction and is positive for products and negative for reactants. a A+ b B Æ c C+ d D 1[] 1[] 1[] 1[] dA dB dC dD R a dt b dt c dt d dt =− = = Reflects mass balance rate of C production rate of A consumption
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Rate law • It is determined either experimentally or theoretically. For complex reactions, the reaction rate can depend on concentrations of both reactants and products. ADP + P i ATP + H 2 O ATPase ] ATP [ K ] ATP [ ] E [ k R m 0 + = (1) (observed) ] Br /[ ] HBr [ 1 ] Br [ ] H [ k R 2 2 2 + = (observed) (2) 2HBr H 2 + Br 2
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For a complex dynamic system, the kinetic model consists of differential equations describing the rate law of each species of interest ( , , ,. .., , , ,. ..) dx f xyz pqr dt = System composition parameters Write down an equation for each species (x, y, z, …) Kinetic modeling: 1) Construction of rate equations based on prior knowledge 2) Estimation of parameters 3) Prediction of dynamics and validation 4) Model refinement
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Rate of elemenary reaction frequency or probability of simultaneous collisions between reacting molecules product of concentrations of reactants.
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This note was uploaded on 08/03/2009 for the course BME 100 taught by Professor Yuan during the Spring '07 term at Duke.

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kinetics - Introduction to reaction kinetics Lingchong You...

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