Lecture 4 - Chemical Kinetics

Lecture 4 - Chemical Kinetics - Reactant and Product vs...

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Reactant and Product vs Time Why Study Chemical Kinetics? Learn how to control and optimize reactions Predict the yield and outcome of a reaction Deduce the molecular mechanism a reaction (i.e. how many steps) What is Chemical Kinetics? Kinetics investigates the rate of chemical reactions and how rate depends on temperature, concentration and catalysts. P R Reactant Product [R](t) [P](t) Time Concentration [] [ ] Δ t P Δ = Δ Δ = t R rate
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Instantaneous Rate of Reaction [] [ ] dt R d dt P d = = rate Reaction rate at specific time point (t 1 ) is called instantaneous rate. [R](t) [P](t) Time Concentration t 1 P R Instantaneous rate equals the slope of the tangent at a specific time (t 1 ). 0 ] [ < dt R d Slope of tangent expressed by a derivative from calculus (e.g. d[P]/dt). Minus sign because Units of rate: M s -1 or M min -1 (i.e. [R] decrease vs t) dP dt dR dt
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Reaction Rate & Rate Law General rate expression determine from balanced eqn: dD cC bB aA + + [ ] [ ] [ ] [ ] dt D d 1 dt C d 1 dt B d 1 dt A d 1 d c b a rate = = = = Divide by stoichiometric coefficient. Add minus sign for each of reactants. Rate law determined empirically: [] [ ] y x B A k rate = [A] vs time Rate vs [A] Reaction order given by x and y
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How to Measure a Rate Law Differential Method (initial rates method) Measure initial reaction rate at several concentrations of reactant. Plot log(rate) vs. log[A] (slope gives reaction order and intercept gives k).
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This note was uploaded on 04/06/2011 for the course CHEM 107B taught by Professor Jamesames during the Winter '09 term at UC Davis.

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Lecture 4 - Chemical Kinetics - Reactant and Product vs...

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