From Chemistry to Electricity Galvanic Cells From Chemistry to Electricity

From Chemistry to Electricity . . . And back again! Electrolytic Cells From Chemistry to Electricity . . . And back again!

Recall: the Galvanic Cell Zn2+ Cu2+ Cu(s) Zn(s) Zn2+ Zn2+ Cu2+ Cu2+

Recall: the Galvanic Cell  Load Current → Conductor Salt Bridge Zn2+ Cu2+ Cu(s) Zn(s) Electrolyte Anode Cathode Zn2+ Cu(s) Zn2+ Cu2+ Oxidation happens here Reduction happens here

Questions: Which way did the electrons go? Why? What happens when we use a different pair of metals?

 Voltage Voltage is also known as electromotive force and potential difference It is a measure of how much energy electrons have to get them moving It is related to the distance between two metals are on the activity series

Analogy Potential Difference e- e- Lithium Potassium Barium Calcium Sodium Magnesium Aluminium Zinc Iron Nickel Lead (Hydrogen) Copper Silver Gold Analogy e- e- Potential Difference

Question: Can we push the electrons back up again?

 The Electrolytic Cell + - External Voltage Na+ Anode Cl- Cathode Electrolyte: eg. NaCl

 The Electrolytic Cell + - External Voltage Cl2(g) Na(s) Anode Cathode Electrolyte: eg. NaCl

Similarities and Differences  Similarities and Differences Galvanic Cells Oxidation occurs at the anode Reduction occurs at the cathode Anode is negative Cathode is positive Does not require external voltage source Changes chemical reactions into electrical energy Electrolytic Cells Oxidation occurs at the anode Reduction occurs at the cathode Anode is positive Cathode is negative Requires external voltage source Changes electrical energy into chemical reactions

Etymology Electrolysis comes from two Greek words: electron and lysis (meaning to break.) Therefore, the word means “breaking apart using electrons

Water Reaction 2 H2O(l) → O2(g) + 4 H+(aq) + 4 e- 2 H2O(l) + 2 e- → H2(g) + 2 OH-(aq)

Water Reaction 2 H2O(l) → O2(g) + 4 H+(aq) + 4 e- 4 H2O(l) + 4 e- → 2 H2(g) + 4 OH-(aq) 6 H2O(l) → 2 H2(g) + O2(g) + 4 H+ + 4 OH-(aq)

The Electrolytic Cell + - O2(g) H2(g) External Voltage Anode Cathode Electrolyte

Practice Where would the hydrolysis reaction be useful? Draw an electrolytic cell for AgBr(l). Draw a galvanic cell for the reaction Au+3 (aq) + Ag(s)  Ag+1 (aq) + Au (s)