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Chemical Reaction Kinetics

Chemical Reaction Kinetics - BME100L:Topic5...

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1 BME 100L: Topic 5 Chemical Reaction Kinetics 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 surroundings >0) for spontaneous processes • At constant T, P (as is 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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2 For example ADP + P i ATP + H 2 O ATPase ADP + P (1) 0' 31 / G kJ mol Δ = − ATP + H2O -ATPase i ATP + H 2 O (2) • The difference between the reactions is the rate! The rate is determined by (a) the mechanisms of reactions. (b) th f t l ti b ff th t ti f ATP th ADP + Pi +ATPase other factors. e.g., solution buffer, the concentration of ATPase, the activitiy of ATPase, and the type of ATPase. • Virtually all metabolic reactions are too slow to support 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 I. 1 Stoichiometry : I. Concepts & Definitions how many molecules of each reactant are converted to how many molecules of each product? a A + b B Æ c C + d D Stoichiometry vector: [ -a -b c d ] Stoichiometric coefficient
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3 Reaction network Æ matrix Reactions The stoichiometric matrix ν A Convention: Products Î positive coefficients Reactants Î negative coefficients or 0 = ν A I.2 Reaction rate: How fast? 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. 1 [ ] 1 [ ] 1 [ ] 1 [ ] d A d B d C d D a A + b B Æ c C + d D R a dt b dt c dt d dt = − = − = = rate of A consumption rate of C production Reflects mass balance
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4 I.3 Rate law: How the rate depends on concentrations of reactants and products It is determined either experimentally or theoretically. For complex reactions, the reaction rate can depend on concentrations of both reactants and products. When the rate depends on the concentration of a product , there’s feedback. ADP + P i ATP + H 2 O ATPase (1) ] ATP [ K ] ATP [ ] E [ k R m 0 + = ( b d) (2) 2HBr H 2 + Br 2 ] Br /[ ] HBr [ 1 ] Br [ ] H [ k R 2 2 2 + = (observed) (observed) Rate of elemenary reaction frequency or probability of simultaneous collisions between reacting molecules product of concentrations of reactants. That is, for an elementary chemical reaction, a A + b B P R = k C A a C B b R : rate of reaction or rate of production of compound P k : rate constant a + b = n , order of reaction . k in general depends on temperature, pressure, electric field, pH, and other quantities, but in general independent of the concentration and time.
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