Chem 113 1st Edition Lecture 12Outline of Last Lecture I. Half-life relationshipsII. Reaction rates, temperature, and the Arrhenius EquationIII. Activation energyIV. Molecular structure and reaction rateOutline of Current LectureI. Multi-step reactionsII. A reaction mechanismCurrent LectureI. Multi-step reactionsa. Many reactions require multiple steps to occurb. Net reactions can have different sets of intermediary reactions that have the same resultsc. One net reaction may be more likely than another version of a net reactionII. A reaction mechanism (step)a. A set of steps that describe molecular interactions to get a total (net) reactionb. Steps are specifically referred to as “elementary steps”, meaning they are the most basic stepi. Describes a collision of molecules of reactants all at onceii. Unimolecular: depends on one reactant molecule1. Example: O3 O2 + O (stratospheric ozone)iii. Bimolecular: depends on two reactant molecules1. Example: O2 + O O3iv. Termolecular: depends on three reactants moleculesThese 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.1. Very rare because it’s hard to make an activated complex out of three piecesc. For an elementary step, the rate law depends on the reactant moleculesi. It matches the stoichiometry of the reactantsii. Rate= k[A]coeffd. Most reactions have several possible mechanisms, experimentally determined rate law can be used to eliminate some mechanismsi. Can’t prove a mechanism, only evidence that supports itii. For a mechanism to be plausible, elementary steps must sum to the next reaction and they have to predict the experimental rate law1. Slow steps in reaction determine the relevance of rate stepsiii. To check the total rate law, we consider all of the steps through the slow
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