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Calculate The Value of E Cell for The Following Reaction

Reviewed by Calculator Editorial Team

The standard cell potential (E cell) is a measure of the tendency of a chemical reaction to occur spontaneously. It's calculated using the Nernst equation, which accounts for the activities of the reactants and products. This guide explains how to calculate E cell for a given redox reaction.

What is E Cell?

The standard cell potential (E cell) represents the maximum electrical potential difference that can be generated by a galvanic cell under standard conditions (25°C, 1 atm pressure, and 1 M concentration for all reactants and products).

For a spontaneous reaction (one that occurs naturally), E cell is positive. For a non-spontaneous reaction, E cell is negative. The magnitude of E cell indicates the driving force of the reaction.

How to Calculate E Cell

The standard cell potential is calculated using the Nernst equation:

Ecell = E0cell - (RT/nF) * ln(Q)

Where:

  • Ecell = Cell potential (V)
  • E0cell = Standard cell potential (V)
  • R = Gas constant (8.314 J/mol·K)
  • T = Temperature (K)
  • n = Number of moles of electrons transferred
  • F = Faraday constant (96,485 C/mol)
  • Q = Reaction quotient

For standard conditions (Q = 1), the equation simplifies to Ecell = E0cell.

Example Calculation

Consider the reaction:

Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)

Given:

  • E0cell = 1.10 V
  • T = 298 K (25°C)
  • n = 2 moles of electrons
  • Initial concentrations: [Cu2+] = 0.01 M, [Zn2+] = 0.01 M

First, calculate the reaction quotient (Q):

Q = [Zn2+]/[Cu2+] = 0.01/0.01 = 1

Since Q = 1, the reaction is at equilibrium and Ecell = E0cell = 1.10 V.

Interpreting Results

The calculated E cell value indicates:

  • If E cell > 0: The reaction is spontaneous and will occur naturally.
  • If E cell = 0: The reaction is at equilibrium.
  • If E cell < 0: The reaction is non-spontaneous and requires energy input to proceed.

The magnitude of E cell shows the voltage produced by the cell. Higher values indicate a stronger driving force for the reaction.

Frequently Asked Questions

What is the difference between standard cell potential and cell potential?

The standard cell potential (E0cell) is measured under standard conditions (1 M concentration, 25°C). The cell potential (Ecell) accounts for actual concentrations and temperature.

How do I find standard reduction potentials?

Standard reduction potentials can be found in chemistry textbooks or online databases like the NIST Chemistry WebBook or the Laidler-Krouse tables.

What units are used for E cell?

E cell is measured in volts (V), which is the standard unit for electrical potential difference.