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UT CH 302 - Random Musings
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CH302 Random Musings April 9, 2010—All the Extra Credits 0. Etiquette Corner. It is amazing how as we grow more comfortable in a setting we tend to forget what makes it possible for human beings to exist in each other’s company without wanting to tear them apart limb from limb. Yes, etiquette is what keeps us civil and the loss of it makes us, at best, not very nice to each other. I can’t control your ability to be civil in the rest of your life, but I can do my best with respect to this course. So a simple reminder that will serve as a guide to perfect classroom behavior, just remember the following and let it guide your actions: You are not the center of the universe. If you remember this, then while I am lecturing you will know that if you talk to your friend, hug in the aisles, develop a sudden urge to leave, decide to update your facebook page, or eat a bag of potato chips, you are keeping someone else from learning. And that isn’t right. Thank you. 1. The score for exam 2 was a 78 for the Thursday exam, the highest in the history of the equilibrium exam in this course. The make-up exam score was not so good—actually it was a perfectly bimodal distribution with the half of the students who knew the material earning an average a little over 80 and the half who did not having an average around 50. I still haven’t had time to address individual concerns about questions—my time is really stretched right now, but I will get to it soon. Sorry about the delay. 2. This is where I remind you to never give up. Many of you came to see me in preparing for the second exam after struggling on the first—some did much better. Some are still getting used to how to do well on this kind of exam. But you have to keep after it. All it takes is getting everything under control and in your head for just one glorious 3 hour period during the final exam in May, and you can have your A for the course as well. To help you prepare, I provide the question types from the final exam at the bottom of the musings. 3. Some good news--the last third of the semester prepares you for the last exam of the semester, one that typically has the highest averages, often in the mid to high 80s. Why? There is a lot of descriptive chemistry to end the course-- a lot of qualitative material that students tend to manage well. To help you get started studying for exam 3, the question types are found at the bottom of the musings. 4. Of course another reason students did well on the second exam is that the electrochem wasn’t included. But it is material to be found on the third exam and makes up the entire fifth quiz which is one week from today. It concerns me that office hour attendance has has very poor this week as folks decompress from the second exam and work in other courses. But this coming week will really need some hard work on the electrochemistry material. 5. The 8 electrochemistry question types are listed below. As always I will provide an electrochemistry practice quiz this weekend and the TAs will provide another Sunday or Monday. • Identifying oxidation and reduction in a chemical reaction • Balancing a chemical reaction in acid or base • Assigning cell convention in an electrochemical cell • Understanding the table of standard half cell reduction potentials • Calculating a standard cell potential • Nernst equation calculation • Ranking oxidizing and reducing agents • Stoichiometry calculation using the Faraday6. We are on to kinetics so as we start, here is an example of kinetics from my own life involving kinetics: Dave figures out how to save hundreds of dollars on potatoes over his lifetime using kinetics concepts Often I shop at WalMart for groceries because they are so darn cheap. Consequently I end up being able to buy a 10 pound bag of potatoes for the cost of a 5 pound bag elsewhere. The problem is that I don’t like making mashed potatoes every night of the week, so the potatoes end up sitting around. Before I know if, they have grown those nasty tentacles, which are so disgusting I end up throwing the potatoes away. Like clockwork, every second week, boom, five pounds of tentacled left-over potatoes tossed—I might as well be shopping at Randall's. Then one day I remembered my kinetics and how maybe all that stuff about rates of reactions of chemicals applied to potatoes as well. I stuck a bag of potatoes in the refrigerator in the garage, and have kept it there for 3 months— no tentacles at all. The only problem is that they are in the garage so I forget I have them and the rate of eating mashed potatoes has gone way down as storage time has soared. 2 months in a refrigerator --yummy mashed potatoes 2 months in the pantry--too gross for words What is particularly enlightening here is that the data that I collected for this kinetics experiments-- concentration versus time data at two different temperatures The data: Day tentacle length (78oF) tentacle length (35oF) 1 0 0 2 0 0 3 0 0 4 0 0 5 2 0 6 3 0 7 5 0 8 7 0 Rate of tentacle growth between days 7 and 8: (35oF) 0 mm per day = (0-0)/(8-7) (78oF) 2 mm per day = (7-5)/(8-7) is exactly the kind of kinetics data that you collect for any kind of kinetics experiment--see worksheet 12 from 2008 which is a really good worksheet to do: http://laude.cm.utexas.edu/courses/ch302/ws12s08.pdf and the source material for next Tuesday's lecture. Note that the data sets are just like the potato data:concentration versus time data at two different temperatures The data: Seconds 300K 310K 0 Unknown starting [C] Unknown starting [C] 1 .12 M .074 M 2 .074 M .027 M 3 .044 M .009 M 4 .027 M .0036 M 5 .016 M .0013 M 6 .009 M .0005 M 8 .0036 M .000067 M 10 .0013 M .0000091 M 7. A bit of advice on what makes kinetics so challenging. In a word: vocabulary. Unlike acid base equilibrium where I spent 2 months teaching you how to reduce the problems to simple common forms like A- or BH+ , the material in kinetics is very broadly and quickly covered and involves concepts that will be unfamiliar even to people who had a lot of chemistry in high school. And to top it off, look at why it all seems like such a blur as you consider trying to distinguish the following phrases from one another: • Rate • Rate expression • Rate constant • Differential rate law • Integrated rate law • Method of initial rate • Rate determining step


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UT CH 302 - Random Musings

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