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.