Questions: What conditions will cause a redox reaction to be nonspontaneous? A. The reduced element is higher on the potential list than the oxidized element. B. The sum of the voltages of the oxidation and reduction halfreactions is positive. C. The half-reaction for the reduced element has a negative standard potential. D. The sum of the voltages of the oxidation and reduction halfreactions is negative.

Solution Steps

• A redox reaction is spontaneous if the overall cell potential (\(E_{\text{cell}}\)) is positive.
• The cell potential is calculated by summing the standard reduction potentials of the oxidation and reduction half-reactions.

• Option A: The position of elements on the potential list does not directly determine spontaneity; it is the sign of the overall cell potential that matters.
• Option B: A positive sum of the voltages indicates a spontaneous reaction, not a nonspontaneous one.
• Option C: A negative standard potential for a half-reaction does not necessarily make the overall reaction nonspontaneous; it depends on the combination with the other half-reaction.
• Option D: A negative sum of the voltages of the oxidation and reduction half-reactions indicates a nonspontaneous reaction.

• The condition that causes a redox reaction to be nonspontaneous is when the sum of the voltages of the oxidation and reduction half-reactions is negative, as stated in Option D.

Final Answer