Electrolysis and Cell Voltage

Electrolysis Process where a nonspontaneous redox rxn occurs from an external energy source Ex: a flashlight powered by batteries Aluminum ore Gold mining Metal plating

Predicting spontaneous rxns Use a metal activity series to predict. Connect the metals, if the line goes down  spontaneous if the line goes up  nonspontaneous

What about Ag and Cu 2+? spontaneous nonspontaneous

Prevention of damage from spontaneous rxns Can be damaging Rust, corrosion How can we prevent the damage? Coating Painting, coating with grease Galvanzing Coating with another easily oxidized metal Cathodic protection Placing a more easily oxidized metal on fuel tanks, pipelines, ship hulls

Cell Voltages Standard Reduction Potential Chart used to determine if a redox rxn is spontaneous (pg. 667 in textbook) If positive, then its spontaneous If negative, then its nonspontaneous

How to calculate Look up reactions on a chart. Record the ε ˚, change the sign if the rxn is oxidized Add the reactions and the voltages Zn  Zn 2+ + 2e- ε ˚ox = 2e- + Cu 2+  Cu ε ˚red = Zn + Cu2+  Zn 2+ + Cu ε ˚cell = 0.76 0.34 1.10V

+ spontaneous - nonspontaneous The voltages are never multiplied by a number can only change the sign of the voltage

Calculate the voltage for Cu + Ag+  Cu2+ + Ag ε ˚ox = ε ˚red = ε ˚cell= Cu  Cu2+ -0.34 0.80 (1e- + Ag +  Ag)2 Cu + 2Ag+  Cu2+ + 2Ag 0.46V

Spontaneous redox rxns Statue of liberty Rusting Batteries (corrosion)