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 Erxn

But only at 1.0 M and 25 deg CAnd DON’T multiply by coefficients!

At any other concentration or temperature: Erxn = Eo

rxn – (RT/nF) ln Q

1. Erxn = Ered + Eox

but also: ln K= (nF/RT) Eorxn

3. A corollary from the Thermodynamic view: The more positive the potential (Eo

rxn, Eored, Eo

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: Cuo + 2 Ag+ Cu2+ + 2 Ago

Cell notation: Cu | Cu2+ || Ag+ | Ago

E- flow

anode cathode

What will happen for this cell? Cuo + Fe3+ Cu2+ + Feo

reagents products

TABLE OF STANDARD REDUCTION POTENTIALSTABLE OF STANDARD REDUCTION POTENTIALSTABLE OF STANDARD REDUCTION POTENTIALSTABLE OF STANDARD REDUCTION POTENTIALS

Eo (V)

Cu2+ + 2e- Cu +0.34

I2 + 2e- 2 I- +0.53

Zn2+ + 2e- Zn -0.76

strongerreducing ability

Ag+ + e- Ag +0.80

Fe3+ + e- Fe +0.772+

Pb2+ + 2e- Pb -0.13

Fe3+ + 3e- Fe -0.04

Al3+ + 3e- Al -1.66

Na+ + e- Na +2.71

K+ + e- K +2.93

2 H+ + 2e- H2 0.00

strongeroxidizing ability

What will happen for this cell? Cuo + Fe3+ Cu2+ + Feo

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): Ecell = Ecathode - Eanode Note

difference!!! Erxn = Ered +

Eox

Electrochemical Cells: how do we make them?

Electrochemical Cells in your life AlkalineDry Cell

Electrochemical Cells in your life

Lead –AcidBattery

The Great Cycle of Energy

G

E Keq

G = -RTlnKG = -n F Erxn

lnK = (nF/RT)Erxn