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Ch.18 - ElectrochemistryWorksheetSee all chapters

Cell Potential: The Nernst Equation

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Sections
Standard Reduction Potentials
Intro to Electrochemical Cells
Galvanic Cell
Electrolytic Cell
Cell Potential: Standard
Cell Potential: The Nernst Equation
Cell Potential and Gibbs Free Energy
Cell Potential and Equilibrium
Cell Potential: G and K
Cell Notation
Electroplating

The Nernst Equation calculates cell potential under non-standard conditions

The Reaction Quotient

Concept #1: The Reaction Quotient is a ratio of product to reactant concentrations at a particular time.

Example #1: What is the reaction quotient for the following redox reaction with the given concentrations?

Pb2+ (aq) + 2 K (s) ⇌ Pb (s) + 2 K+(aq)                  [Pb2+] = 0.0880 M          [K+] = 0.0015 M

Calculate Nonstandard Cell Potential

Concept #2: The Nernst Equation is used to find the cell potential when ion concentration(s) do not equal 1 M.

Example #2: Calculate the cell potential for a reaction at 25.0ºC when given the following ionic concentrations and standard reduction potentials.

2 Co3+ (aq) + 3 Mg (s) ⇌ 2 Co (s) + 3 Mg2+(aq)                    [Co3+] = 1.0 M    [Mg2+] = 0.0033 M

Standard Reduction Potentials

Co3+ (aq) + 3 e  →. Co (s)                       E°red = + 1.82 V
Mg2+ (aq) + 2 e  →. Mg (s)                     E°red = – 2.37 V

Practice: If [Br –] = 0.010 M and [Al3+] = 0.022 M, predict whether the following reaction would proceed spontaneously as written at 25ºC:

Al (s)  +  Br2 (l)  ⇌. Al3+ (aq) +  Br – (aq)

Standard Reduction Potentials

Al3+ (aq) + 3 e  →  Al (s)               E°red = – 1.66 V

Br2 (l) + 2 e 2  →  Br (aq)          E°red = + 1.09 V

Practice: Determine [Fe2+] for the following galvanic cell at 25ºC if given [Sn2+] = 0.072 M, [Fe3+] = 0.0219 M, and [Sn4+] = 0.00345 M.

Sn2+ (aq) + 2 Fe3+ (aq)  ⇌. Sn4+ (aq) + 2 Fe2+ (aq)     Ecell = + 0.68 V

Standard Reduction Potentials

Sn4+ (aq) + 2 e  →. Sn2+ (aq)      E°red = + 0.151 V

Fe3+ (aq) + e  →  Fe2+ (aq)         E°red = + 0.771 V