CHAPTER 16 (pages 776-792) Oxidation and Reduction Galvanic Cells, Half Reactions (E°anode & E°cathode) Standard Reduction Potential (E°) Nernst Equation, and the dependence of Potential on Concentration Relationship between Equilibrium Constant and Standard Potential Driving Force, ΔG and E

REDOX REACTIONS MnO2 + 4 HBr ⇋ MnBr2 + Br2 + 2 H2O 3 H2S + 2 NO3– + 2 H+ ⇋ 3 S + 2 NO + 4 H2O

OBSERVED REDOX PROCESSES

GALVANIC CELLS

INERT ELECTRODES

STANDARD REDUCTION POTENTIALS

MEASURING STANDARD POTENTIALS

CALCULATING STANDARD CELL POTENTIAL Al(s) + NO3−(aq) + 4 H+(aq) ⇋ Al3+(aq) + NO(g) + 2 H2O(l)

ADDITIONAL EXAMPLE Fe(s) + Mg2+(aq) ⇋ Fe2+(aq) + Mg(s)

ox: Fe(s)  Fe2+(aq) + 2 e− E = +0.45 V red: Pb2+(aq) + 2 e−  Pb(s) E = −0.13 V tot: Pb2+(aq) + Fe(s)  Fe2+(aq) + Pb(s) E = +0.32 V

ELECTROMOTIVE POTENTIAL

Figure: 18-10-06UN Title: Thermodynamic terms, with equations Caption: Cell potential, free energy, and the equilibrium constant are all related.

E°CELL, ΔG° AND K Under standard state conditions, a reaction will spontaneously proceeds in the forward direction if: ΔG° < 1 (negative) E° > 1 (positive) K > 1

Design a voltaic cell with the following half cells and complete the calculations: Ag+ (aq) + 1e-  Ag (s) Eo = 0.80 V Pb2+ (aq) + 2e-  Pb (s) Eo = -0.13 V Calculate the Eocell (potential at standard conditions) Calculate Go. Calculate  Calculate the Ecell if [Ag+] = 2.0 M and [Pb2+] = 1.0 x 10-4 M.

Williams, spring 2009 stop here

Design a voltaic cell with the following half cells and complete the calculations: Ag+ (aq) + 1e-  Ag (s) Eo = 0.80 V Pb2+ (aq) + 2e-  Pb (s) Eo = -0.13 V Calculate the Eocell (potential at standard conditions)

Design a voltaic cell with the following half cells and complete the calculations: Ag+ (aq) + 1e-  Ag (s) Eo = 0.80 V Pb2+ (aq) + 2e-  Pb (s) Eo = -0.13 V Calculate Go.

Design a voltaic cell with the following half cells and complete the calculations: Ag+ (aq) + 1e-  Ag (s) Eo = 0.80 V Pb2+ (aq) + 2e-  Pb (s) Eo = -0.13 V Calculate 

Design a voltaic cell with the following half cells and complete the calculations: Ag+ (aq) + 1e-  Ag (s) Eo = 0.80 V Pb2+ (aq) + 2e-  Pb (s) Eo = -0.13 V Calculate the Ecell if [Ag+] = 2.0 M and Pb2+] = 1.0 x 10-4 M.

Figure: 18-12 Title: Cu/Cu2+ Concentration Cell Caption: If the two half-cells have the same Cu2+ concentration, the cell potential is zero. If one half-cell has a greater Cu2+ concentration than the other, a spontaneous reaction occurs. In the reaction, Cu2+ ions in the more concentrated cell are reduced (to solid copper), while Cu2+ ions in the more dilute cell are formed (from solid copper). In effect, the concentration of copper ions in the two half-cells tends toward equality.

OBJECTIVE 11.4: PROVIDE A THOROUGH OVERVIEW OF APPLICATIONS OF ELECTROCHEMICAL CELLS INCLUDING FUEL CELLS, CORROSION, AND OTHER TOPICS AS TIME PERMITS.

CORROSION corrosion is the spontaneous oxidation of a metal by chemicals in the environment since many materials we use are active metals, corrosion can be a very big problem

RUSTING rust is hydrated iron(III) oxide moisture must be present electrolytes promote rusting acids promote rusting lower pH = lower E°red

Dry Cell Batteries Figure: 18-15a,b Title: Dry-Cell Batteries Caption: (a) In a common dry-cell battery, the zinc case acts as the anode and a graphite rod immersed in a moist, slightly acidic paste of MnO2 and NH4Cl acts as the cathode. (b) The longer-lived alkaline batteries now in common use employ a graphite cathode immersed in a paste of MnO2 and a base.

Lead – Acid Storage Battery Figure: 18-16 Title: Lead-Acid Storage Battery Caption: A lead-acid storage battery consists of six cells wired in series. Each cell contains a porous lead anode and a lead oxide cathode, both immersed in sulfuric acid.

Biological Electrochemistry Figure: 18-13 Title: Potential Changes Across the Nerve Cell Membrane Caption: The changes in ion concentrations that take place when a nerve cell is stimulated result in a spike in the electrochemical potential across the membrane.

Lithium Ion Battery Figure: 18-17 Title: Lithium Ion Battery Caption: In the lithium ion battery, the spontaneous flow of lithium ions from the graphite anode to the lithium transition metal oxide cathode causes a corresponding flow of electrons in the external circuit.

Figure: 18-18 Title: Hydrogen-Oxygen Fuel Cell Caption: In this fuel cell, hydrogen and oxygen combine to form water.

Figure: 18-19a,b Title: Fuel-Cell Breathalyzer Caption: The fuel-cell breathalyzer works by oxidizing ethyl alcohol in the breath to acetic acid. The electrical current that is produced is proportional to the concentration of ethyl alcohol in the breath.