Impact of NON-Standard Conditions on Voltaic Cells

Using NERST Eqn

Help ! Help! My battery is dead!

• As redox rxn progresses, concentrations of ions in anode + cathode cell changes.

• Eventually, flow of e- stops, E = 0 and … cell is dead.

• Cell will discharge e- until it reaches equilibrium, termed the dead cell, Q = K and E = 0.

At equilibrium, G = 0.

Effect of [Concentration] on Ecell

• NERST Eqn takes into account solns NOT at 1M:Gibbs Free Energy G

Gas Constant R (8.31 J/mol-K)

Temperature in (K)elvin

Mol n

Faraday’s Constant F

Cell Potential Ecell

Reaction Quotient Q [Products]/[Reactants]

The NERST Equation

• Use NERST to explore ion concentration changes during redox reactions.

@ 25 °C

Sample Exercise 20.11 p. 850

Sample Exercise 20.12 p. 850

TAKE HOME MESSAGE p. 850

• Increasing [reactants] or decreasing [products] results in HIGH E!

• Decreasing [reactants] or increasing [products] results in LOW E!

• In comparison with E at Standard Conditions.