Cell Potential and Free Energy - AP Chemistry

1. What is Faraday's constant value?

   $96485 \text{ C/mol}$. Conversion factor between moles of electrons and electric charge.

2. Why is the standard hydrogen electrode used as a reference?

   Assigned a potential of 0.00 V. Provides a universal standard for comparing electrode potentials.

3. What is the effect of a catalyst on cell potential?

   No effect on cell potential. Catalysts affect reaction rate but not thermodynamic quantities.

4. Determine the spontaneity: $E^0_\text{cell} = -0.76 \text{ V}$.

   Non-spontaneous reaction. Negative standard cell potential indicates $\triangle G^0 > 0$, non-spontaneous.

5. What is the effect of increasing reactant concentration on cell potential?

   Increases cell potential. Higher reactant concentration makes $Q$ smaller, increasing $E$.

6. Determine the effect on $E$ when product concentration increases.

   Decreases cell potential. Higher product concentration increases $Q$, reducing cell potential.

7. What is the relationship between $\triangle G^0$ and reaction spontaneity?

   $\triangle G^0 < 0$ indicates spontaneity. Negative standard free energy indicates spontaneous process under standard conditions.

8. What is the concentration of ions in a standard solution?

   $1 \text{ M}$. Standard concentration for aqueous ionic solutions in electrochemistry.

9. What is the standard cell potential for a galvanic cell?

   The cell potential under standard conditions. Measured when all species are at standard conditions (1 M, 1 atm, 25°C).

10. What is the direction of electron flow in a galvanic cell?

    From anode to cathode. Electrons move from negative anode to positive cathode through external circuit.

11. Calculate $\triangle G$ for a cell with $n=2$, $F=96485 \text{ C/mol}$, and $E=1.5 \text{ V}$.

    $\triangle G = -289455 \text{ J/mol}$. Using $\triangle G = -nFE$ with given values: $-(2)(96485)(1.5)$.

12. State the unit of cell potential.

    Volts (V). Standard SI unit for electric potential difference.

13. What does a zero cell potential mean in a galvanic cell?

    The cell is at equilibrium. No potential difference means equilibrium between electrodes.

14. What does a negative $\triangle G$ indicate about a reaction?

    The reaction is spontaneous. Negative free energy change indicates thermodynamically favorable process.

15. What does a negative cell potential indicate about a reaction's spontaneity?

    The reaction is non-spontaneous. Negative $E$ means $\triangle G > 0$, thermodynamically unfavorable.

16. Calculate $E$ for $E^0_\text{cell} = 1.10 \text{ V}$, $T = 298 \text{ K}$, $n=2$, $Q=0.1$.

    $E > 1.10 \text{ V}$. When $Q < 1$, the Nernst equation predicts $E > E^0$.

17. What is the $\triangle G^0$ for a reaction at equilibrium?

    $\triangle G^0 = 0$. At equilibrium, forward and reverse reactions have equal rates.

18. State the Nernst equation for electrochemical cells.

    $E = E^0 - \frac{RT}{nF} \times \text{ln}Q$. Relates cell potential to standard potential and reaction quotient.

19. What is the standard reduction potential of a hydrogen electrode?

    0.00 V. Serves as the reference point for measuring all other electrode potentials.

20. Identify the temperature used for standard conditions in electrochemistry.

    $298 \text{ K}$. Standard temperature for electrochemical measurements (25°C).

21. State the relationship between $K_{eq}$ and $E^0_\text{cell}$.

    $E^0_\text{cell} = \frac{RT}{nF} \times \ln K_{eq}$. Equilibrium constant relates to standard cell potential through thermodynamics.

22. Which factor affects cell potential according to the Nernst equation?

    Concentration of reactants and products. The reaction quotient $Q$ in the Nernst equation depends on species concentrations.

23. Calculate $\triangle G^0$ given $n=3$, $F=96485 \text{ C/mol}$, $E^0_\text{cell}=1.2 \text{ V}$.

    $\triangle G^0 = -347346 \text{ J/mol}$. Using $\triangle G^0 = -nFE^0$ with given values: $-(3)(96485)(1.2)$.

24. Calculate the cell potential given $E^0_\text{cell} = 1.10 \text{ V}$ and $Q = 1.0$ at $298 \text{ K}$.

    $E = E^0_\text{cell} = 1.10 \text{ V}$. When $Q = 1$, the Nernst equation reduces to $E = E^0$.

25. Calculate the equilibrium constant, $K_{eq}$, for $E^0_\text{cell} = 0.0592 \text{ V}$ at $298 \text{ K}$.

    $K_{eq} \text{ is large (spontaneous)}$. Positive $E^0$ indicates large equilibrium constant favoring products.

26. What is the standard condition for pressure in electrochemistry?

    1 atm. Standard atmospheric pressure for electrochemical measurements.

27. What is the equation for standard free energy change, $\triangle G^0$?

    $\triangle G^0 = -nFE^0_\text{cell}$. Standard free energy relates to standard cell potential through Faraday's constant.

28. Find the cell potential with $E^0_\text{cell} = 0.44 \text{ V}$ and $Q = 10$ at $298 \text{ K}$.

    $E < 0.44 \text{ V}$. Nernst equation shows $E$ decreases when $Q > 1$ compared to $E^0$.

29. Identify the relationship between free energy and cell potential.

    $\Delta G = -nFE$. Shows Gibbs free energy is proportional to cell potential times electrons and Faraday's constant.

30. State the relationship between $E^0_\text{cell}$ and $\triangle G^0$ for spontaneous reactions.

    $E^0_\text{cell} > 0, \triangle G^0 < 0$. Spontaneous reactions have positive cell potential and negative free energy.

31. Identify the formula for the change in Gibbs free energy, $\triangle G$, in terms of $E$.

    $\triangle G = -nFE$. Direct relationship between free energy change and electrochemical potential.

32. How does temperature affect cell potential?

    Alters $E$ via the Nernst equation. Temperature appears in the $RT/nF$ term of the Nernst equation.

33. What is the formula for the equilibrium constant in terms of $\triangle G^0$?

    $\triangle G^0 = -RT \times \text{ln}K_{eq}$. Connects equilibrium constant to standard free energy change.

34. State the condition under which $E^0_\text{cell} = 0$.

    Equilibrium is established. Zero cell potential means no driving force for electron flow.

35. What is the role of the salt bridge in a galvanic cell?

    To maintain electrical neutrality. Allows ion migration to balance charge buildup at electrodes.

36. What does a positive cell potential indicate about a reaction's spontaneity?

    The reaction is spontaneous. Positive $E$ means $\triangle G < 0$, indicating thermodynamic favorability.

37. What is the primary purpose of the Nernst equation?

    To calculate cell potential under non-standard conditions. Adjusts standard cell potential for actual concentration and temperature conditions.

38. Determine the spontaneity: $\triangle G = 0$.

    Reaction is at equilibrium. Zero free energy change indicates no net driving force for reaction.

39. What is the standard reduction potential of a hydrogen electrode?

    0.00 V. Serves as the reference point for measuring all other electrode potentials.

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