CHEM 113 9/12 Lecture 8 Outline of Last Lecture I. Using Example 1 to practice problems of reaction mechanisms Outline of Current Lecture II. More practice of reaction mechanismsCurrent LectureIn class, more practice with reaction mechanisms were discussed. All practice problems and solutions can be found on the course website.Here is an outline of the types of problems we have been doing Here are the elementary steps of a reaction1). A + B X(fast)2). X + C Y (slow)3). Y D (fast)a). What is the overall balanced equation?By canceling out the intermediates and adding up the reactants and products the following equation was determinedA+B+C Db). Identify the intermediates.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.X & Y are variables that act as both reactants and products and are therefore the intermediates.Some problems may ask about transition states, which are determined by n+1, where n is the number of intermediates present in the reaction.c). What is the molecularity of each step?The molecularity is how many molecules are interacting at each step of the reactionStep 1: bimolecular because there are two variables, A & BStep 2: also bimolecularStep 3: Unimoleculard). Is this consistent with the overall observed rate law?Here we are comparing the observed rate law and the rate law of the rate-determining step to make sure they are consistent. So our observed rate law is Rate= k[A][B][C]This can be deduced using the overall balanced equation.Now we take out rate law for step 2, which is the rate-determining step because it is the slowest.Rate= k2[X][C]However we need to rearrange this because there are intermediates included. To do this we usethe rate law for step 1.Since the first step is described with , we can set the two sides equal to each other.k1[A][B]= k-1[X]Then we manipulate the equation to equal [X], or the intermediate concentration.[X]= k1[A][B]/ k-1We then substitute this into the rate law of the rate-determining step.Rate 2= k2 (k1[A][B]/ k-1) [C]Rate 2= ((k2*k1)/k-1) [A][B][C]Because k is a constant, (k2*k1)/k-1 = k and therefore our equation matches the overall observed rate
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