CHEM 1120 Edition 1nd Lecture 7 Outline of Last Lecture I Half Life a Equations for each order II How can we control the rate of a chemical reaction III Temperature and Rate a Collision Model b Activation Energy c Arrhenius Equation Outline of Current Lecture I Arrhenius Equation a How do we know it is true II Reaction Mechanisms a Elementary step b Molecularity c Current Lecture I II Arrhenius Equation a How do we know it is true i Measure k at different temperatures ii Plot k vs temp iii Must be exponential iv Plot ln k E R 1 T ln A should be linear 1 Slope E R Reaction Mechanisms a Reaction mechanism the sequence of elementary steps resulting in an overall chemical reaction b Elementary step a simple reaction having no intermediates and having only one transition state also elementary reaction or elementary process These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute c If you are going to write a rate law only want to write it in terms of things you know things that go in and go out don t measure intermediates i Intermediates NOT an elementary step ii A B B C B would be an intermediate step d If a reaction equation represents an elementary step then the reaction coefficients are related to the orders of the rate law e How is a mechanism judged as acceptable i Sum of elementary steps must result in overall reaction ii Mechanism must be consistent with the experimentally determined rate law f Since elementary steps are simple collision processes their rate laws are determined by their molecularity i Unimolecular A products Rate k A ii Bimolecular A A or A B products Rate k A 2 or k A B iii Termolecular A A A or A A B or A B C products g Rate determining step a mechanism s slowest step i Determines the overall reaction rate ii Larger activation energy slower step h
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