Lecture5 - Chemical kinetics Physical Chemistry Lecture 5...

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1 Physical Chemistry Lecture 5 Theoretical chemical kinetics Chemical kinetics Understand the nature of reactions Predict reaction outcomes based on Reactants Conditions Requires integration of theory and experimental results Temperature dependence of rate constants Empirical theory of Arrhenius gives a useful way to parameterize rate constants A pre-exponential factor E a activation energy Often seen in analysis of kinetic data ) / exp( ) ( RT E A T k a Non-Arrhenius behavior Arrhenius behavior is empirical For some reactions the temperature dependence of the rate constant is not exponential Theory does not easily predict Arrhenius form Amazing that Arrhenius behavior is so often seen Elementary reactions Chemical reactions are often more complex than presented and do not occur as a single step Some reactions do occur in a single step -- elementary reactions Generally involve simple mono- or bimolecular interactions Order in elementary reactions is the stoichiometry number, called molecularity 1 1 2 1 2 2 2 2 ] [ ] [ ] [ ] [ 2 Br H k v HBr Br H O H k v O H O H Simple collision theory of gas- phase kinetics To participate in a bimolecular reaction, molecules must approach each other SCT: gas-phase reaction rate proportional to collision frequency SCT does not generally agree with experimental rates Points out how to think about theory of chemical reactions B A AB B A AB AB AB AB C C kT L n n v Z v Z v
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Lecture5 - Chemical kinetics Physical Chemistry Lecture 5...

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