A reaction has E°cell = -0.25 V. Under standard conditions, is it spontaneous as written?

• A. No; E°cell < 0 indicates nonspontaneous as written
• B. Yes; E°cell > 0 indicates spontaneous
• C. It depends on concentrations
• D. Spontaneous only at high temperatures

Answer: (A)

Spontaneity of a redox reaction under standard conditions is determined by the sign of E°cell: a positive value means the reaction proceeds spontaneously in the written direction, while a negative value means it does not. With E°cell = -0.25 V, the forward (written) direction has a negative driving force, so it is nonspontaneous under standard conditions (ΔG° = -nF E°cell would be positive). The reverse direction, however, would have a positive E°cell (+0.25 V) and would be spontaneous. Since the question specifies standard conditions, the given negative E°cell confirms nonspontaneity in the written direction; the other options don’t apply under these standard conditions.