Cell Potential Under Nonstandard Conditions

Cell Potential Under Nonstandard Conditions

Overview

  • The cell potential under nonstandard conditions is similarly determined like cell potential under standard conditions, yet it allows for the fact that charge, temperature, and chemical concentration can vary.
  • The Nernst equation modifies the standard cell potential based on changes in these factors.

Nernst Equation

  • The Nernst equation connects the observed cell potential to the standard cell potential, reaction quotient, temperature, and number of electrons transferred in the redox reaction.
  • The formula is E = E° - (RT/nF) * lnQ, where:
    • E is the non-standard cell potential,
    • E° is the standard cell potential,
    • R is the universal gas constant (8.314 J K^-1 mol^-1),
    • T is the temperature in Kelvin,
    • n is the number of electrons exchanged per molecule,
    • F is the Faraday constant (96485 C mol^-1),
    • Q is the reaction quotient.

Effects of Variables on the Nernst Equation

  • Temperature: The temperature within the Nernst equation is always stated in Kelvin. As the temperature increases, the cell potential reduces due to the increase in the entropy of the system.
  • Reaction Quotient (Q): Charged species within half reactions, in either gas or aqueous phase, influence Q. As Q rises, the cell potential tends to reduce. If Q is less than one, the cell runs more strongly than the standard potential would predict.

Calculating Q - Reaction Quotient

  • The calculation of Q is similar to that of the equilibrium constant, K. It is the ratio of products to reactants, with each concentration or pressure raised to the power of its coefficient in the balanced chemical equation. However, Q can be calculated at any time in the course of the reaction, not just at equilibrium.

Significance of Nernst Equation in Real World

  • The Nernst equation is critical in calculating the accurate cell potential under nonstandard conditions, which are usually encountered in real-life, making it an essential tool for chemists and engineers.
  • This equation is also vital for understanding and predicting the behaviour of batteries, fuel cells, electrolysis systems, and other electrochemical systems.