Chapter 10.7 Electrolysis

Electrolytic Cell Recall the galvanic cell: Spontaneous overall reaction Cell potential has a positive value Converts chemical energy into electrical energy Electrons flow from a higher potential energy to a lower potential energy Electrical energy can be used to move electrons from a lower potential energy to a higher potential energy A cell that uses energy to do this is called an electrolytic cell

Electrolytic Cell Converts electrical energy into chemical energy Process is called electrolysis Overall reaction is non-spontaneous, requires energy Includes electrodes, at least one electrolyte, an external source of electricity, and external circuit Possible for electrolytic cells to have the two half-reactions take place in the same container

Galvanic Cell vs. Electrolytic Cell Spontaneous reaction Converts chemical energy to electrical energy Anode (negative): zinc Cathode (positive): copper Oxidation at anode: Zn  Zn2+ + 2e- Reduction at cathode: Cu2+ + 2e-  Cu Cell Reaction: Zn + Cu2+  Zn2+ + Cu Electrons move to cathode Anions move to anode Cations move to cathode Non-spontaneous reaction Converts electrical energy to chemical energy Anode (positive): copper Cathode (negative): zinc Oxidation at anode: Cu  Cu2+ + 2e- Reduction at cathode: Zn2+ + 2e-  Zn Cell Reaction: Cu + Zn2+  Cu2+ + Zn Electrons move to cathode Anions move to anode Cations move to cathode

Predicting Products of Electrolysis Make a list of all substances present. Label all possible oxidizing and reducing agents present. (Don’t forget water for aqueous solutions) Use the redox table to identify the strongest oxidizing agent. Write the equation for the reduction half-reaction that occurs at the cathode, including the reduction potential Use the redox table to identify the strongest reducing agent. Write the equation for the oxidation half-reaction that occurs at the anode, including the reduction potential Balance electrons and write the equation for the overall (or net) reaction. Calculate the cell potential: Eor(cell) = Eor(cathode) – Eor(anode)

Practice Predict the products and find the cell potential for the electrolysis of 1 mol/L LiBr(aq).

HOMEWORK Read p.667 – 669 and make notes P.670 #1-9