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Calculate E Cell for The Following Equation

Reviewed by Calculator Editorial Team

The electromotive force (E cell) is a measure of the potential difference between the two half-cells in an electrochemical cell. This calculator helps you determine the E cell for any given redox reaction by using standard reduction potentials.

What is E Cell?

The electromotive force (E cell) represents the maximum electrical potential difference between the two electrodes of an electrochemical cell when no current is flowing. It's calculated using the standard reduction potentials of the half-reactions involved.

For a spontaneous reaction (where E cell is positive), the cell will produce electricity. For a non-spontaneous reaction (where E cell is negative), the cell will require an external power source to operate.

How to Calculate E Cell

The E cell is calculated using the Nernst equation for standard conditions:

Ecell = Ered - Eox

Where:

  • Ecell is the cell potential (V)
  • Ered is the standard reduction potential of the reduction half-reaction (V)
  • Eox is the standard reduction potential of the oxidation half-reaction (V)

To use this formula:

  1. Identify the oxidation and reduction half-reactions
  2. Find the standard reduction potentials for each half-reaction
  3. Subtract the oxidation potential from the reduction potential

Standard Reduction Potentials

Standard reduction potentials are measured in volts (V) and represent the potential difference when the reaction is at standard conditions (1 M concentration, 25°C, 1 atm pressure).

Common standard reduction potentials include:

Half-Reaction Standard Reduction Potential (V)
F2(g) + 2e- → 2F-(aq) +2.87
Cl2(g) + 2e- → 2Cl-(aq) +1.36
Br2(l) + 2e- → 2Br-(aq) +1.09
I2(s) + 2e- → 2I-(aq) +0.54
2H+(aq) + 2e- → H2(g) 0.00

Example Calculation

Let's calculate the E cell for the following reaction:

2Ag+(aq) + Cu(s) → 2Ag(s) + Cu2+(aq)

Step 1: Identify the half-reactions

  • Oxidation: Cu(s) → Cu2+(aq) + 2e-
  • Reduction: 2Ag+(aq) + 2e- → 2Ag(s)

Step 2: Find the standard reduction potentials

  • Ered for Ag+/Ag: +0.80 V
  • Eox for Cu2+/Cu: +0.34 V

Step 3: Calculate E cell

Ecell = Ered - Eox = 0.80 V - 0.34 V = 0.46 V

The calculated E cell is 0.46 volts, indicating this is a spontaneous reaction.

FAQ

What is the difference between E cell and E° cell?
E cell is the actual cell potential under specific conditions, while E° cell is the standard cell potential at standard conditions (1 M concentration, 25°C).
How do I know if a reaction is spontaneous?
A reaction is spontaneous if the E cell is positive. If E cell is negative, the reaction is non-spontaneous and requires an external power source.
What factors affect the E cell?
Temperature, concentration of reactants/products, and pressure can all affect the E cell from its standard value.
Can I use this calculator for non-standard conditions?
This calculator provides standard cell potentials. For non-standard conditions, you would need to use the Nernst equation with activity coefficients.