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AP Chemistry Practice Quiz: Cell Potential and Free Energy

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 10 questions to check your progress.

Question 1 of 10

According to the principles of electrochemistry, a redox reaction in a cell is considered thermodynamically favored when it exhibits which of the following characteristics?

All Questions (10)

According to the principles of electrochemistry, a redox reaction in a cell is considered thermodynamically favored when it exhibits which of the following characteristics?

A) A negative voltage, requiring an external potential.

B) A positive voltage.

C) A standard cell potential of zero.

D) A positive standard Gibbs free energy change.

Correct Answer: B

The provided content states that reactions are thermodynamically favored if they have a positive voltage. A negative voltage indicates an unfavored reaction, and a positive Gibbs free energy change also corresponds to an unfavored reaction.

Which statement correctly describes the relationship between the standard cell potential (E°) and the thermodynamic favorability of a reaction?

A) A positive E° indicates a thermodynamically unfavored reaction.

B) A negative E° indicates a thermodynamically favored reaction.

C) A positive E° indicates a thermodynamically favored reaction.

D) The sign of E° is unrelated to thermodynamic favorability.

Correct Answer: C

The content explicitly states that a positive E° means a favored reaction, while a negative E° means an unfavored reaction.

Based on the equation ΔG° = −nFE°, what is the relationship between standard Gibbs free energy (ΔG°) and standard cell potential (E°) for a thermodynamically favored electrochemical reaction?

A) E° is positive, and ΔG° is positive.

B) E° is negative, and ΔG° is negative.

C) E° is positive, and ΔG° is negative.

D) E° is negative, and ΔG° is positive.

Correct Answer: C

A thermodynamically favored reaction has a positive E°. According to the equation ΔG° = −nFE°, if E° is positive, the negative sign in the formula ensures that ΔG° will be negative (since n and F are positive constants).

An electrochemical cell is constructed and found to have a negative standard cell potential (E°). What can be concluded about this cell?

A) The reaction is thermodynamically favored and will proceed spontaneously.

B) The standard Gibbs free energy change (ΔG°) is negative.

C) The reaction is thermodynamically unfavored and requires an external potential.

D) The cell has reached equilibrium.

Correct Answer: C

The content specifies that a negative voltage (negative E°) corresponds to a thermodynamically unfavored reaction that requires an external potential to proceed.

The equation ΔG° = −nFE° demonstrates that the standard Gibbs free energy change is proportional to what?

A) The number of moles of electrons (n) only.

B) The positive value of the cell potential (E°).

C) The negative of the cell potential (−E°).

D) Faraday's constant (F) only.

Correct Answer: C

The equation ΔG° = −nFE° shows a direct proportionality between ΔG° and the term −E°. As E° becomes more positive, ΔG° becomes more negative.

How is the overall standard cell potential (E°) for an electrochemical cell calculated?

A) By measuring the final temperature of the cell.

B) By identifying the oxidation and reduction half-reactions and using their standard reduction potentials.

C) By dividing the Gibbs free energy by Faraday's constant.

D) By measuring the pressure of any gases produced in the cell.

Correct Answer: B

The provided content explicitly states that the standard cell potential is calculated by identifying the oxidation and reduction half-reactions and their respective standard reduction potentials.

If a redox reaction in an electrochemical cell has a positive standard Gibbs free energy change (ΔG° > 0), what must be true about its standard cell potential (E°)?

A) E° must be positive.

B) E° must be negative.

C) E° must be zero.

D) The sign of E° cannot be determined from ΔG°.

Correct Answer: B

From the relationship ΔG° = −nFE°, if ΔG° is positive, then −nFE° must be positive. Since n and F are positive constants, E° must be negative for the entire term to be positive.

Which of the following correctly explains the thermodynamic implications of the equation ΔG° = −nFE°?

A) A reaction becomes more favored as its standard cell potential becomes less positive.

B) A positive standard cell potential results in a negative standard Gibbs free energy change, signifying a favored reaction.

C) A negative standard cell potential results in a negative standard Gibbs free energy change, signifying a favored reaction.

D) The thermodynamic favorability is determined by n and F, not the cell potential E°.

Correct Answer: B

The equation links a positive E° to a negative ΔG°. The content confirms that a positive E° and a negative ΔG° are both indicators of a thermodynamically favored reaction.

A student claims that an electrochemical cell with a negative ΔG° is thermodynamically unfavored. Why is this claim incorrect?

A) The claim is correct; a negative ΔG° means the reaction requires energy input.

B) A negative ΔG° corresponds to a negative E°, which means the reaction is unfavored.

C) A negative ΔG° indicates a thermodynamically favored reaction.

D) The sign of ΔG° is not related to whether a reaction is favored or unfavored.

Correct Answer: C

The provided content explicitly states that a favored reaction has a negative ΔG°. Therefore, the student's claim is incorrect.

To determine if an electrochemical cell is thermodynamically favored, one must evaluate its standard cell potential (E°) and the constituent half-reactions. A favored reaction will always have:

A) A negative E° and a positive ΔG°.

B) A positive E° and a positive ΔG°.

C) A negative E° and a negative ΔG°.

D) A positive E° and a negative ΔG°.

Correct Answer: D

This question synthesizes the core concepts. A thermodynamically favored reaction is defined by having a positive standard cell potential (E°) and, consequently, a negative standard Gibbs free energy change (ΔG°), as dictated by the relationship ΔG° = −nFE°.