Electrolysis and Cell Voltage Electrolysis Process where a

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 2+ + 2 eε ˚ox = 0. 76 2 e- + Cu 2+ Cu ε ˚red = 0. 34 Zn + Cu 2+ Zn 2+ + Cu ε ˚cell = 1. 10 V

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

Calculate the voltage for Cu + Ag+ Cu 2+ + Ag Cu 2+ + 2 e(1 e- + Ag + Ag)2 Cu + 2 Ag+ Cu 2+ + 2 Ag ε ˚ox = -0. 34 ε ˚red = 0. 80 ε ˚cell= 0. 46 V

Spontaneous redox rxns Statue of liberty Rusting Batteries (corrosion)