A galvanic cell is constructed using zinc (E° = −0.76 V) and copper (E° = +0.34 V). What is the standard cell potential, and what does its sign tell you?
AE°cell = +1.10 V; the reaction is spontaneous as written
BE°cell = −1.10 V; the reaction requires external energy to proceed
CE°cell = +0.42 V; the reaction is spontaneous but weakly
DE°cell = −0.42 V; the copper electrode is being oxidized
E°cell = E°cathode − E°anode = +0.34 − (−0.76) = +1.10 V. A positive cell potential means ΔG° is negative (via ΔG° = −nFE°cell), confirming the reaction is spontaneous. Copper is reduced at the cathode; zinc is oxidized at the anode.
Question 2 Multiple Choice
In an electrolytic cell used to electroplate copper onto a metal surface, what must be true about the applied external voltage compared to the reverse cell potential?
AThe applied voltage must exceed the reverse cell potential to force the non-spontaneous reaction to proceed
BAny small voltage will work because electrolytic cells harness spontaneous reactions
CThe applied voltage must equal exactly the standard cell potential of the galvanic cell
DNo external voltage is needed; the salt bridge provides the driving force
Electrolytic cells run non-spontaneous reactions by applying external electrical energy. The applied voltage must exceed the reverse cell potential to overcome the thermodynamic barrier (ΔG > 0). This is the reverse of a galvanic cell, which converts spontaneous chemical energy to electrical work.
Question 3 True / False
In both galvanic and electrolytic cells, oxidation always occurs at the anode.
TTrue
FFalse
Answer: True
By definition, the anode is the electrode where oxidation (loss of electrons) occurs, regardless of cell type. In a galvanic cell the anode is negative (electrons flow out spontaneously); in an electrolytic cell the anode is positive (connected to the + terminal of the power source). The label 'anode' is defined by the chemistry, not the polarity.
Question 4 True / False
A positive standard cell potential (E°cell > 0) means the electrochemical reaction requires energy input from an external source.
TTrue
FFalse
Answer: False
A positive E°cell means the reaction is spontaneous — it releases free energy. This is confirmed by ΔG° = −nFE°cell: positive E°cell gives negative ΔG°, meaning the system can do work. It is negative E°cell that indicates a non-spontaneous reaction requiring external energy, as in electrolytic cells.
Question 5 Short Answer
Why does physically separating the two half-reactions of a redox reaction — as in a galvanic cell — allow you to extract electrical work, even though the overall chemical reaction is the same as if the reactants were mixed directly?
Think about your answer, then reveal below.
Model answer: When reactants are mixed, electrons transfer directly between species and the energy is released as heat. Separating the half-reactions forces electrons to travel through an external circuit to reach the reduction half-cell. This directed electron flow constitutes an electric current, allowing the chemical energy to be converted into useful electrical work rather than dissipated as heat.
The key insight is that the thermodynamics are identical — the same ΔG is available — but the pathway determines whether energy becomes heat or work. A galvanic cell exploits the spatial separation of oxidation and reduction to channel the electron transfer through a circuit, converting chemical potential energy to electrical energy. This is the foundational principle of every battery.