Which statement correctly describes the standard reduction potential and how to compute a cell potential?

• A. E° is the intrinsic tendency to gain electrons under standard conditions; the cell potential is calculated by E°cell = E°cathode − E°anode.
• B. E° is the rate constant for electron transfer; E°cell = E°cathode − E°anode.
• C. E° is the intrinsic tendency to gain electrons under standard conditions; E°cell = E°cathode − E°anode; balance electrons when combining half-reactions.
• D. E° is a measure of pH; E°cell = E°cathode + E°anode.

Answer: (C)

The main idea here is that E° tells you how much a species wants to gain electrons under standard conditions (it measures the tendency to be reduced). When you form a galvanic cell, the species with the higher tendency to be reduced becomes the cathode, and the one with the lower tendency to be reduced becomes the anode.

To get the standard cell potential, you use the reduction potentials of the two half-reactions: E°cell = E°red(cathode) − E°red(anode). This difference gives you the overall driving force for the cell under standard conditions. If E°cell is positive, the reaction is spontaneous under those conditions.

When you actually combine the half-reactions to write the full cell equation, you must balance electrons so that the number of electrons lost equals the number gained. This balancing ensures you have a correct overall reaction, even though the numerical value of E°cell comes from the reduction potentials themselves.

The other statements aren’t correct because E° is not a rate constant and it is not a measure of pH; it represents the tendency to gain electrons, and the cell potential uses the reduction potentials of the cathode and anode with the electrons-balanced half-reactions in mind.