notes_Lecture_13_110310

notes_Lecture_13_110310 - Lecture 13: Cell Potential and G...

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Lecture 13: Cell Potential and Δ G Announcements: – HW #4 due today (by 11pm)! – HW #5 posted, due Nov. 10 Reading: Outline – “Line notation” for electrochemical cells (not in book) – Cell potential, electrical work, and free energy (11.3, 10.12) – E o cell and K (11.4) Problems for Extra Practice – 21, 35, 37, 41, 43 (Chapter 11)
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Galvanic Cell Shorthand Shorthand Notation Zn(s)|Zn +2 (aq)||Cu +2 (aq)|Cu(s) Anode Cathode Salt bridge Phase boundaries are indicated by a single line.
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How do you write the line-notation for a galvanic cell that has an aqueous or gaseous component instead of a solid metal? Ag(s)|Ag + (aq)||H + (aq)|O 2 (g)|Pt(s) Ag + Ag OH Pt O 2 - (aq) Salt Bridge V > 0 H + (aq) Pt(s)|Fe 2+ (aq), Fe 3+ (aq)||Ag + (aq)|Ag(s)
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Cell potential and work • We have seen how to construct an electrochemical cell that is capable of generating a spontaneous flow of electrons. ..such a cell is called galvanic . • The flow of electrons (current) can be used to perform work on the surroundings. • Recall the definition of electromotive force (emf): Volt = work (J)/charge (C) • In English: 1 J of work is done when 1 C of charge is transferred between two points in the circuit that differ by a potential of 1V.
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• Recall, we have a system-based perspective. This means that work done by the system is negative : • Rearranging: w = work done by system (J) q = charge (C) (not heat!!) cell w E q - = cell qE w = - The E cell measured by a potentiometer gives the maximum potential at zero current flow. Once electrons are allowed to flow through the circuit, the actual potential they experience changes with time, because the driving force for the reaction decreases as the system approaches equilibrium. So the time-averaged potential the electrons actually experience is less
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notes_Lecture_13_110310 - Lecture 13: Cell Potential and G...

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