S10_Student_Lecture_06

# S10_Student_Lecture_06 - Announcements HW4 due this Fri(HW5...

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Announcements 2/1/10 HW4 due this Fri. (HW5 released). Exam I NEXT Monday night, Feb. 8. 8 PM Practice questions will be (are) posted Check Blackboard for your seat assignment in Elliott Lab this week: Be Prepared (see next slides!)

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Using Spectroscopy to Using Spectroscopy to Determine Concentration Determine Concentration BEER-LAMBERT LAW: There is a linear relation between A and c for a given path length and compound. A = absorbance l = path length ε = molar absorptivity c = concentration This means you can find unknown solution concentration if A is measured. A c
Determining the Rate Law Determining the Rate Law for a Reaction in the Laboratory for a Reaction in the Laboratory You will: find λmax for crystal violet calibrate the Spec20 using standards of known concentration use the Spec20 and LabView to measure and collect concentration vs. time data write the rate law for the reaction of crystal violet with sodium hydroxide READ: Chapter 4 in the lab manual. Complete the prelab questions found on p. 33. CV + + OH - W CVOH violet colorless

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Writing the Rate Law Writing the Rate Law Using Experimental Data Using Experimental Data CV + + OH - W CVOH violet colorless Determine the reaction order in CV + : Plot [CV + ] vs. time, ln[CV + ] vs. time, and 1/[CV + ]. Wwhich plot is linear? Repeat the reaction with 2 other concentrations of OH - . Calculate the order of the reaction in OH - . Calculate k. Write the rate law. Read the entire experiment before you come to lab. An outline of the experiment will be helpful.
Reaction Mechanisms Mechanism : The stepwise changes the reactant molecules actually undergo during a reaction. Intermediates : do not appear in overall reaction but are essential for reaction to occur Elementary Reactions : individual simplest steps Using reaction orders to understand mechanism Intermediates 2A + B E + F (Overall reaction) A +B C C + A D D E + F A + B + C + A + D C + D + E + F 2A + B E + F

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Mechanisms Most rxns. involve a sequence of elementary steps. 2 I - + H 2 O 2 + 2 H + ---> I 2 + 2 H 2 O Rate = k [I - ] [H 2 O 2 ] NOTE: 1.Rate law comes from experiment 2.Order and stoichiometric coefficients not necessarily the same! 3.Rate law reflects all chemistry down to and including the slowest step in multistep reaction.
Elementary Reactions Molecularity: # of reactant molecules involved in the elementary reaction 1. ___________ One molecule or ion collides with a unreactive molecule or the wall of the container and gives products. 2. ___________

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S10_Student_Lecture_06 - Announcements HW4 due this Fri(HW5...

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