Standard cell potential tells how strongly a galvanic cell can push electrons through an external circuit under standard conditions. It is the voltage, or EMF, produced when oxidation at the anode is paired with reduction at the cathode. This idea matters because it connects electron transfer reactions to measurable electrical energy.
Batteries, corrosion, electroplating, and many sensors all depend on cell potentials.
Key Facts
- Standard conditions are 1.0 M solutions, 1 atm gases, and 25 °C unless stated otherwise.
- Oxidation occurs at the anode, and reduction occurs at the cathode.
- Electrons flow through the wire from anode to cathode in a galvanic cell.
- E°cell = E°cathode - E°anode using standard reduction potentials.
- A positive E°cell means the reaction is spontaneous under standard conditions.
- ΔG° = -nFE°cell, where n is moles of electrons and F = 96485 C/mol e-.
Vocabulary
- Standard cell potential
- The voltage of an electrochemical cell measured under standard conditions.
- EMF
- Electromotive force is the maximum voltage a cell can provide when no current is flowing.
- Anode
- The electrode where oxidation occurs and electrons are produced.
- Cathode
- The electrode where reduction occurs and electrons are consumed.
- Salt bridge
- A connection containing mobile ions that keeps charge balanced in the two half-cells.
Common Mistakes to Avoid
- Adding the two reduction potentials directly is wrong because one half-reaction must be oxidation, so use E°cell = E°cathode - E°anode.
- Changing the sign of a reduction potential after multiplying a half-reaction is wrong because electrode potentials are intensive and do not scale with coefficients.
- Calling the cathode negative in every cell is wrong because the cathode is positive in a galvanic cell but negative in an electrolytic cell.
- Forgetting the salt bridge is wrong because charge buildup would quickly stop electron flow even if the redox reaction is favorable.
Practice Questions
- 1 A galvanic cell uses Zn2+/Zn with E°red = -0.76 V and Cu2+/Cu with E°red = +0.34 V. Identify the anode and cathode, then calculate E°cell.
- 2 For a cell with E°cathode = +0.80 V and E°anode = -0.14 V, calculate E°cell and decide whether the reaction is spontaneous under standard conditions.
- 3 A student reverses the anode and cathode labels in a galvanic cell diagram. Explain how this affects the predicted electron flow, sign of E°cell, and spontaneity.