1. NERNST EQUATION Chapter 20
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2. What causes the electrical potential of an electrochemical cell?
The electrical potential of a voltaic cell is a measure of the cell’s ability to produce an electric current.
Electrical potential is usually measured in volts (V).
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3. Electrical Potential
The standard cell potential (E0cell) is the measured cell potential when the ion concentrations in the half-cells are 1M, any gases are at a pressure of 101 kPa, and the temperature is 25°C.
E0cell = E0red – E0oxid
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5. E0cell = E0red – E0oxid 2.00 V = 0.34 V – (-1.66 V)
Sample Problem 21.1
Cu2+(aq) + 2e– →Cu(s) E0Cu2+ = 0.34 V
Al3+(aq) + 3e– → Al(s) E0Al3+ = V
E0cell = E0red – E0oxid
2.00 V = 0.34 V – (-1.66 V)
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6. What determines the measured
If Al and Cu are separated work is done by the electrons. Voltmeter is used to measure the energy.
What determines the measured
value?

7. AP SHEET

8. NERNST EQUATION E at Nonstandard Conditions
E = potential under nonstandard conditions
n = no. of electrons exchanged
ln = “natural log”
If [P] and [R] = 1 mol/L, then E = E˚

9. NERNST EQUATION E at Nonstandard Conditions
If [R](bottom) > [P], Q <1, ln is neg
then E is ______________ than E˚
greater
If [R](bottom) < [P], Q >1, ln is pos
then E is ______________ than E˚
less

12. X X
Q = [ Zn2+]
[Ag+]2 X

13. Hw

14. AP Question

15. Is E˚ related to ∆G?
YES!

16. Eo and ∆Go
Eo is related to ∆Go, the free energy change for the reaction.
∆Go = - n F Eo
where F = Faraday constant = x 104 J/V•mol
and n is the number of moles of electrons transferred
Michael Faraday

17. ∆Go = - n F Eo For a product-favored reaction
Reactants ----> Products
∆Go < 0 and so Eo > 0
Eo is positive
For a reactant-favored reaction
Reactants <---- Products
∆Go > 0 and so Eo < 0
Eo is negative

19. Eo = v
∆Go = - n F Eo

20. HW

21. Is E˚ related to K?
YES!

22. AP SHEET

23. R= J/(mol K)