505Electrolysis

505Electrolysis - Cell potentials and equilibrium constants...

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Lesson 25 1 Lesson 25 Cell potentials and equilibrium constants What happens when a galvanic cell achieves equilibrium? Q nF RT E E cell cell ln 0 Nernst equation for non-equilibrium conditions: Nernst equation when chemical equilibrium is reached ( Q = K c ): RT nF E K K nF RT E cell c c cell 0 0 exp ln 0 Use this expression to calculate equilibrium constants using galvanic cells Lesson 25 Example 1 Is Cu + a stable ion in aqueous solution? To decide this, first determine the equilibrium constant for the reaction: 2 Cu + = Cu 2+ + Cu Use two different pairs of half-reactions in your calculation. Note that they have different E 0 values but the same K c value. Lesson 25 Example 2 Knowing that, Fe 3+ + e → Fe 2+ E o Fe3+/Fe2+ = 0.77 V Fe 2+ + 2 e → Fe E o Fe2+/Fe = –0.44 V calculate the value of E o Fe3+/Fe for: Fe 3+ + 3 e → Fe
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Lesson 25 2 Lesson 25 Electrolysis If an opposing external potential causes the reaction in a galvanic
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505Electrolysis - Cell potentials and equilibrium constants...

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