Question

question 2 of 25
what property characterizes a spontaneous redox reaction?
a. a negative sum of the two half - reactions standard potentials
b. a positive reduction potential for the reduction half - reaction
c. a positive sum of the two half - reactions standard potentials
d. a positive oxidation potential for the oxidation half - reaction

Explanation:

Step1: Recall redox - reaction principle

For a spontaneous redox reaction, the cell potential ($E_{cell}^{\circ}$) is positive. The cell potential is calculated as the sum of the standard reduction potential of the reduction half - reaction and the standard oxidation potential of the oxidation half - reaction. Mathematically, $E_{cell}^{\circ}=E_{cathode}^{\circ}+E_{anode}^{\circ}$, where $E_{cathode}^{\circ}$ is the standard reduction potential of the reduction half - reaction and $E_{anode}^{\circ}$ is the standard oxidation potential of the oxidation half - reaction. Another way to write it is $E_{cell}^{\circ}=E_{red}^{\circ}-E_{ox}^{\circ}$ (where $E_{red}^{\circ}$ and $E_{ox}^{\circ}$ are the standard reduction potentials of the reduction and oxidation half - reactions respectively). A positive $E_{cell}^{\circ}$ indicates a spontaneous reaction.

Step2: Analyze each option

• Option A: A negative sum of the two half - reactions' standard potentials means $E_{cell}^{\circ}<0$, which indicates a non - spontaneous reaction.
• Option B: Just having a positive reduction potential for the reduction half - reaction is not sufficient to determine spontaneity. We need to consider both half - reactions.
• Option C: A positive sum of the two half - reactions' standard potentials means $E_{cell}^{\circ}>0$, which characterizes a spontaneous redox reaction.
• Option D: Just having a positive oxidation potential for the oxidation half - reaction is not sufficient to determine spontaneity. We need to consider both half - reactions.

Answer:

C. A positive sum of the two half - reactions' standard potentials