Lecture 3-eq calcs_1

Lecture 3-eq calcs_1 - Chemistry 271 Fall 2009 General...

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09/09/09 1 Chemistry 271, Fall 2009 General Chemistry and Energetics Lecture #3: Equilibrium Constants, Calculations, Intro to Acid-Base Jason D. Kahn Dept. of Chemistry and Biochemistry [email protected]
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Lecture 3, Chemistry 271, Fall 2009, Jason Kahn Course Mechanics Discussion sections have started. Old exams are/will be available at http://www.biochem.umd.edu/biochem/kahn/previous_exams/index.html Dan’s office hours are not part of the gen-chem office hour pool, and vice versa. You need not contact me about missing class unless you will miss an exam or a quiz. Any issues with getting hold of the textbook/e-book? The first SmartWork assignment is available, due 9/14/09. Questions from Chapters 6 and 15. Ungraded intro questions are also available for training. You have unlimited retries on homework problems.
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Lecture 3, Chemistry 271, Fall 2009, Jason Kahn Lecture 2, Chemistry 271, Fall 2009, Jason Kahn Slide 3 What is LeChatelier’s Principle Good For, or Not? It guides intuition. It’s a reality check on the results of computations. Practicing chemists and biochemists talk about driving a reaction by adding reactants, removing product, or changing the conditions all the time. But there is nothing you can learn from LeChatelier that can’t be made more quantitative using real thermodynamics. Leonard K. Nash, Elements of Chemical Thermodynamics , p. 108, referring to the ability to carry out a numerical calculation of a change in the composition of an equilibrium mixture: “…And this is everywhere the superior relationship in which quantitative thermodynamics stands to the purely qualitative Le Chatelier principle.”
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Lecture 3, Chemistry 271, Fall 2009, Jason Kahn Review Equilibrium and LeChatelier Equilibrium is dynamic: forward and reverse reactions both occur, but at the same rate. LeChatelier’s principle is that upon a change in the conditions, the system will respond to reduce the imposed change. Adding reactants drives the reaction toward products to decrease the reactant concentration. The equilibrium constant puts this idea on a quantitative basis: at equilibrium, the “reaction quotient” of reactant and product concentrations is equal to K eq .
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Fall 2009, Jason Kahn Lecture 2, Chemistry 271, Fall 2009, Jason Kahn Slide 5 The Reaction Quotient Q On the way to making LeChatelier quantitative For the general reaction a A + b B c C + d D Q has the same form as the equilibrium constant, but it is calculated from the concentrations actually present, without regard to whether the system is at equilibrium. LeChatelier just says that Q will change to approach K! Q
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This note was uploaded on 01/24/2011 for the course CHEM 271 taught by Professor Staff during the Spring '08 term at Maryland.

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Lecture 3-eq calcs_1 - Chemistry 271 Fall 2009 General...

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