CH116lecture23P

CH116lecture23P - UMass Boston Chem 116 CHEM 116...

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UMass Boston, Chem 116 ©H.Sev ian CHEM 116 Electrochemistry at Non-Standard Conditions, and Intro to Thermodynamics Lecture 23 Prof. Sevian Important announcement: If you borrowed a clicker from me this semester, return it to me at the end of next lecture or at the final exam If you do not return it, you will receive an INC for your grade Today’s agenda z Big picture of electrochemistry z Redox reactions and oxidation numbers (last lecture) z Charge flow in electrochemical cells and diagramming a cell z Using the mathematical model to predict current and voltage under standard and non-standard conditions z Important points of thermodynamics for general chemistry z Enthalpy change (+endothermic, –exothermic) z Entropy change (+more disorder, –more order) z Gibbs free energy (+non-spontaneous, –spontaneous) z Connection to equilibrium z Connection to electrochemistry Announcements z Final exam is Tuesday, Dec 16, 3:00-6:00pm in S-1-006
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UMass Boston, Chem 116 ©H.Sev ian Predicting voltage under standard conditions z Voltage = cell potential ( E o cell ) = related to Δ G , which is related to H , T , and S z Table of reference voltages, all referenced to the hydrogen half-cell z All reference voltages are reduction potentials, so if you need an oxidation potential you just take the opposite z See table of standard reduction potentials z Example of using standard reduction potentials to predict E o cell Non-standard conditions: Nernst equation z Concentrations of solutions not at standard 1.0 M z Temperature not at standard 25 ºC where F is the Faraday constant: F = 96,500 C/mol Q n E Q n E E o cell o cell cell log 0592 . 0 ln 0257 . 0 = = Q n RT E E o cell cell ln = Least common multiple of electrons exchanged in the redox reaction Reaction quotient http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/electroChem /voltaicCellEMF.html set up Cu|Cu 2+ (0.001M)||Ag + (2.0M)|Ag cell
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UMass Boston, Chem 116 ©H.Sev ian Electrolysis: electrochemical cell forced to run backwards (against its will) z Note: sections 20.7 and 20.8 in the text book are fascinating reading, but they are not required reading. However, section 20.9 is required reading. z Electroplating : The longer you run the cell, the more metal electroplate builds up z Current means how many electrons pass by per second z If you know how much metal electroplate you want to make, then stoichiometry tells you how many electrons are required z Cu 2+ ( aq ) + 2 e¯ Cu ( s ) z Au 3+ ( aq ) + 3 e¯ Au ( s ) z Ag + ( aq ) + 1 e¯ Ag ( s ) z If you know what current is being applied (e.g., 0.800 amperes = 0.800 Coulombs/second), then you can figure out how much time you must run the cell for in order to build the amount of electroplated metal that you want Electrolysis example Similar to Sample Exercise 20.14, pp. 885-886 Calculate the mass of O 2 produced in the electrolysis of water, using a current of 0.445 A for a period of 45 minutes.
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UMass Boston, Chem 116 ©H.Sev ian Overview of thermodynamics Thermodynamics Reaction extent Reaction direction predicts Equilibrium constant, K Calculated using Δ G o = - RT ln K
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CH116lecture23P - UMass Boston Chem 116 CHEM 116...

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