What must you do to the sign of the Eoxidation reaction when calculating Ecell?

What must you do to the sign of the Eoxidation reaction when calculating Ecell?

• A. Leave unchanged
• B. Take the absolute value
• C. Reverse the sign
• D. Multiply by n

Answer: (C)

Standard electrode potentials are listed for reduction directions. When you combine two half-reactions to find E°cell, you use the reduction potentials for both halves. If you write the oxidation half-reaction, its potential corresponds to the opposite direction, so you must flip its sign. In other words, the oxidation potential is the negative of the reduction potential for the same couple, E°ox = -E°red. Therefore, to use the oxidation half in the E°cell calculation, you reverse its sign so that you’re effectively using the corresponding reduction potential in the E°cell formula (E°cell = E°cathode − E°anode).

Standard electrode potentials are listed for reduction directions. When you combine two half-reactions to find E°cell, you use the reduction potentials for both halves. If you write the oxidation half-reaction, its potential corresponds to the opposite direction, so you must flip its sign. In other words, the oxidation potential is the negative of the reduction potential for the same couple, E°ox = -E°red. Therefore, to use the oxidation half in the E°cell calculation, you reverse its sign so that you’re effectively using the corresponding reduction potential in the E°cell formula (E°cell = E°cathode − E°anode).