Chemistry Clarity · chemistryclarity.com

The Nernst Equation: Flashcards

Revise the Nernst equation, why cell potential falls, concentration cells and the links between E°, ΔG° and K.

10 cardsIntermediate

10 cards

  1. Question
    State the Nernst equation.
    Answer

    E=E°−RTnFln⁡QE = E° - \dfrac{RT}{nF}\ln Q

  2. Question
    Give the Nernst equation at 25 °C with log.
    Answer

    E=E°−0.0592 Vnlog⁡QE = E° - \dfrac{0.0592\ \text{V}}{n}\log Q

  3. Question
    Why does a battery's voltage fall as it is used?
    Answer

    Products build up and reactants are used, so Q increases and E decreases.

  4. Question
    What is E when the cell reaction reaches equilibrium?
    Answer

    Zero: Q = K and the battery is flat.

  5. Question
    What is a concentration cell?
    Answer

    A cell with the same electrode reaction on both sides but different concentrations; E° = 0 but E is not zero.

  6. Question
    In a concentration cell, which side is the anode?
    Answer

    The more dilute side (it is oxidized, raising its concentration).

  7. Question
    Give the relationship between ΔG° and E°.
    Answer

    ΔG°=−nFE°\Delta G° = -nFE°, with F = 96 485 C/mol.

  8. Question
    Give the relationship between E° and K at 25 °C.
    Answer

    log⁡K=nE°0.0592 V\log K = \dfrac{nE°}{0.0592\ \text{V}}

  9. Question
    A cell has E° = 1.10 V and n = 2. What is K at 25 °C?
    Answer

    log K = 2 × 1.10 ÷ 0.0592 = 37.16, so K = 1.5 × 10³⁷.

  10. Question
    If E° is positive, what are the signs of ΔG° and the size of K?
    Answer

    ΔG° negative and K greater than 1: spontaneous, products favoured.