Standard cell potential is a fundamental concept in IB Chemistry. It explains how much electrical energy a galvanic or electrolytic cell can produce or require. Understanding standard cell potential helps students predict reaction direction, determine spontaneity, and calculate overall voltage for electrochemical cells. Once mastered, this concept makes redox questions far more intuitive and manageable.
What Is Standard Cell Potential?
Standard cell potential (E°cell) is the voltage produced by an electrochemical cell under standard conditions.
Standard conditions include:
- 1.00 mol dm⁻³ ion concentrations
- 1 atm pressure for gases
- 298 K (25°C) temperature
Standard cell potential represents the electrical driving force of a redox reaction.
How E°cell Is Calculated
A galvanic cell consists of two half-cells:
- One for oxidation
- One for reduction
Each half-reaction has a standard reduction potential (E°) listed in data booklets.
To calculate the overall cell potential:
E°cell = E°cathode – E°anode
Key rules:
- You always subtract the anode value
- Even if the half-reaction is reversed, never change the sign of the E° value
- Coefficients never affect E° values
This formula determines the voltage the cell can produce.
Example Calculation
Given:
Zn²⁺ + 2e⁻ → Zn(s) E° = –0.76 V
Cu²⁺ + 2e⁻ → Cu(s) E° = +0.34 V
