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Thinking Like a Chemist About Electrochemistry III Potential, Free - - PowerPoint PPT Presentation
Thinking Like a Chemist About Electrochemistry III Potential, Free - - PowerPoint PPT Presentation
Thinking Like a Chemist About Electrochemistry III Potential, Free Energy & K UNIT 8 DAY 6 What are we going to learn today? Determine Voltage in Electrochemical Cells Containing Different Concentrations of Reactants Relationship between
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Relationship between E and ∆G ∆G is energy E is electrical potential Electric work (energy) = charge X potential work = -charge X E ∆G = workmax ∆G = - charge X Emax From now on we’ll know the Potential we calculate is the theoretical maximum Real world never actually that good
REVIEW FROM LAST CLASS
∆G = - nFE
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Work on PART 2 of “Extracting Work from Chemical Change” Activity, starting on #7
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#7: What is the maximum amount of electrical work that can be extracted from running this cell under standard conditions.
- A. 2316 kJ/mol
- B. 1158 kJ/mol
- C. 579 kJ/mol
- D. 239 kJ/mol
Poll: Clicker Question
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#10: What can you say about Q?
- A. Q<K and reaction will proceed towards
products.
- B. Q<K and reaction will proceed towards
reactants.
- C. Q>K and reaction will proceed towards
products.
- D. Q>K and reaction will proceed towards
reactants.
Poll: Clicker Question
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- nFE = -nFE° + RTlnQ
DERIVE NERNST EQUATION
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E = Eº - (0.0591/n) log (Q) #12: Calculate the emf of the cell: Al(s)|Al3+(aq, 0.001 M) ||Cu2+(aq, 0.01 M) |Cu(s)
- A. 1.8 V
- B. 1.9 V
- C. 2 V
- D. 2.1 V
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#12: Calculate the emf of the cell: Al(s)|Al3+(aq, 1 M) ||Cu2+(aq, 1 x 10-8 M) |Cu(s)
- A. 1.55 V
- B. 1.76 V
- C. 2 V
- D. 2.24 V
E = Eº - (0.0591/n) log (Q)
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Nernst Equation – Dependence of Cell Potential on Concentration Think about what happens to the value of E when the value of Q changes!
E = Eº - (0.0591/n) log (Q)
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NERNST EQUATION USED TO DETERMINE CONCENTRATION
Cu (s) I Cu2+ (.001M) II Cu2+ (1M) I Cu (s)
E = Eº - 0.0591 log (Q) n
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Nernst Equation – Dependence of Cell Potential on Concentration Calculate the emf of the cell: Cu(s)|Cu2+(aq, .001 M) ||Cu2+(aq,1 M) |Cu(s)
- A. +0.176 V
- B. -0.176 V
- C. +0.088 V
- D. -0.088 V
- E. zero
Poll: Clicker Question
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Think about why this cell produces a voltage: Cu(s)|Cu2+(aq, .001 M) ||Cu2+(aq,1 M) |Cu(s)
EXPLAIN IN TERMS OF FREE ENERGY HOW THIS CELL PRODUCES A VOLTAGE a) More concentrated cell lower free energy b) Less concentrated cell lower free energy c) Chemical reaction is moving in a direction to maximize free energy
Poll: Clicker Question
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What did we learn today?
Calculate the cell potential for a nonstandard cell. Describe fully the relationship between the free energy and the cell potential. Describe fully the relationship between cell potential and the equilibrium constant. Explain thermodynamically the operation of a concentration cell, and be able to predict the concentration in the cell based
- n the cell potential.
Understand the relationship between charge delivered or produced and the amount of reactant used or product formed for both galvanic and electrolytic cells.
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