Previously in Chem104: It’s not all about Batteries: The Great Cycle of Energy Not at Standard? Membrane Potentials Today in Chem104: Electron Transfer Concepts overview Why we need electrochemical cells Cell notation conventions

Electron Transfer Reactions: The BIG PICTURE Major Concepts and Equations 2. The Thermodynamic view:  G = -n F E rxn But only at 1.0 M and 25 deg C And DON’T multiply by coefficients! At any other concentration or temperature: E rxn = E o rxn – (RT/nF) ln Q 1. E rxn = E red + E ox but also: ln K= (nF/RT) E o rxn 3. A corollary from the Thermodynamic view: The more positive the potential (E o rxn, E o red, E o ox ) the more thermodynamically favored it is.

Why we need Electrochemical Cells (First a demo...) To convert Energy to (useful) Work How does a cell do that? Separate the two half reactions To convert electron transfer (movement) to an electrical current

Electrochemical Cells: how do we make them?

Cell Notation Reaction: Cu o + 2 Ag +  Cu Ag o Cell notation: Cu | Cu 2+ || Ag + | Ag o E- flow anodecathode

What will happen for this cell? Cu o + Fe 3+  Cu 2+ + Fe o reagents products

TABLE OF STANDARD REDUCTION POTENTIALS E o (V) Cu e-  Cu+0.34 I2I2 + 2e-  2 I Zn e-  Zn-0.76 stronger reducing ability Ag + + e-  Ag+0.80 Fe 3+ + e-  Fe Pb e-  Pb-0.13 Fe e-  Fe-0.04 Al e-  Al-1.66Na + + e-  Na+2.71 K + + e-  K H + + 2e-  H stronger oxidizing ability

What will happen for this cell? Cu o + Fe 3+  Cu 2+ + Fe o reagents products

Electrochemical Cells: terms to know Cells that do Spontaneous Electron Transfer: Galvanic or Voltaic Cells for Non-Spontaneous Electron Transfer: Electrolytic *these require another energy source, a battery Cell Components: Anode – where oxidation —anodic rxn—occurs, (-) charged; Cathode – where reduction occurs—cathodic rxn—occurs, (+) charged Cell Potential (EMF): E cell = E cathode - E anode Note difference !!! E rxn = E red + E ox

Electrochemical Cells: how do we make them?

Electrochemical Cells in your lifeAlkaline Dry Cell

Electrochemical Cells in your life Lead –Acid Battery

The Great Cycle of Energy GG EK eq  G = -RTlnK  G = -n F E rxn lnK = (nF/RT)E rxn