last chapter! Chapter 19: Electron Transfer Reactions Main Concepts: 1.Redox Reactions consist of two halves, Oxidation and Reduction 2.Reaction Potential, E rxn, in Redox Reactions 3.Nernst Equation adjusts E o rxn to make E rxn 4.Electrochemical Cells (in two flavors) used to get useful work from redox reactions

Electron Transfer Reactions Reaction Potential, E rxn, in Redox Reactions How does this relate to Free Energy? How do you write redox reactions? How can you predict spontaneous redox reaction? Let’s watch one in action!

Electron Transfer Reactions: contrast to Acid/Base AH + B  A- + BH+ thermodynamics Acid: H+ donor K: extent of forward rxn Base: H+ acceptor  G = -RTlnK  G < 0, spont. acid strength: K a base strength: K b Acid/base reactions occur in pairs: need an acid and a base, a H+ donor and a H+ acceptor

Electron Transfer Reactions: parallels to Acid/Base X red + Y ox  X ox + Y red thermodynamics X red = reductant: e- donorE rxn, “EMF”, potential Y ox = oxidant: e- acceptor  G < 0, spont.  G = -n F E rxn reductant strength: E red oxidant strength: E ox Redox reactions occur in pairs: need a reductant and an oxidant, an e- donor and an e- acceptor

Electron Transfer Reactions: contrast to Acid/Base AH + B  A- + BH+ Acid: H+ donor K: extent of forward rxn Base: H+ acceptor  G = -RTlnK  G < 0, spont. acid strength: K a base strength: K b X red + Y ox  X ox + Y red X red = reductant: e- donorE rxn, EMF, potential Y ox = oxidant: e- acceptor  G < 0, spont.  G = -n F E rxn reductant strength: E red oxidant strength: E ox

Electron Transfer Reactions Let’s see one in action! Then answer these questions: What was the reaction? What was the electron transfer? What was the reductant? What was the oxidant? What is the reduction half reaction? What is the oxidation half reaction?

Electron Transfer Reactions Further questions: What is the sum of the ox and red half reactions? Was it spontaneous? What is the sign of  G? What is the sign of E rxn, the reaction potential? What is the magnitude of E rxn ?

Determining Reaction Potential by Calculation E rxn = E red + E ox

Where Do I Find E red + E ox ?

Determining Reaction Potential by Calculation E rxn = E red + E ox Ag+ + e-  Ag E red = V Cu(2+) + 2e-  Cu E red = V Cu  Cu(2+) + 2e- E ox = V 2 Ag+ + Cu  2Ag + Cu(2+) E rxn = V E rxn = E red +E ox = = V

Determining Free Energy from E rxn 2 Ag+ + Cu  2Ag + Cu(2+) E rxn = V  G = -n F E rxn  G = -2 x (9.65 x 10 4 C/mol) e- x E rxn  G = - 89,166 J = -89 kJ 1 volt = 1 Joule/Coulomb