The standard cell potential, denoted as E°cell, is calculated under standard conditions (298 K or 25°C, 1 atm pressure, and 1M concentrations). It represents the voltage of an electrochemical cell when all reactants and products are in their standard states. According to the provided reference, you determine E°cell by subtracting the standard reduction potential (E°) of the anode from the standard reduction potential (E°) of the cathode.
Understanding E°cell Calculation
Key Concepts
- Standard Conditions: These are specific conditions used for measuring and comparing electrochemical data.
- Anode: The electrode where oxidation occurs (loss of electrons).
- Cathode: The electrode where reduction occurs (gain of electrons).
- Standard Reduction Potential (E°): The potential of a half-cell measured under standard conditions, with respect to the standard hydrogen electrode (SHE), which is assigned a value of 0V. These are usually provided in a table of standard reduction potentials.
Formula for E°cell Calculation
E°cell = E°(cathode) - E°(anode)
Step-by-Step Calculation
- Identify the Anode and Cathode: Determine which half-reaction is oxidation (anode) and which is reduction (cathode) in the overall electrochemical reaction.
- Find Standard Reduction Potentials: Locate the standard reduction potentials (E°) for both half-reactions in a table of standard reduction potentials.
- Apply the Formula: Use the formula E°cell = E°(cathode) - E°(anode) to calculate the standard cell potential.
Example Calculation
Let's say we have a cell with the following half-reactions:
- Zn2+(aq) + 2e- → Zn(s) E° = -0.76 V (Anode)
- Cu2+(aq) + 2e- → Cu(s) E° = +0.34 V (Cathode)
Then, the E°cell is calculated as:
E°cell = +0.34 V - (-0.76 V) = +1.10 V
Key Difference: E°cell vs. Ecell
It is important to note, as the reference states, the difference between E°cell and Ecell. E°cell (standard cell potential) is calculated under standard conditions, whereas Ecell refers to the cell potential under non-standard conditions (e.g. different temperatures or concentrations). For Ecell you have to use the Nernst equation.
Summary Table
| Property | E°cell (Standard Cell Potential) | Ecell (Cell Potential) |
|---|---|---|
| Conditions | Standard (298K, 1 atm, 1 M concentrations) | Non-standard |
| Calculation Method | E°(cathode) - E°(anode) | Nernst equation |
| Use | Theoretical potential under ideal conditions | Potential of cell under non-standard conditions |
