Home > Chemistry, Uncategorized > Chemistry1A Part Deux: Lecture 29 Notes

Chemistry1A Part Deux: Lecture 29 Notes

Overview

Today is a 52 minute lecture on electrochemistry.  This is a difficult topic, and it takes time to get used to the notations. 

Details

The direction of electron transfer in redox reaction can be determined from electron energies, expressed as electrode potentials.

Combustion reactions heat a gas.  This is how we generate electricity, power for transportation, etc.  The efficiency is only 30%.  Most goes into making the molecules move faster.

LEO goes GER – loss of electrons is oxidation, gain of electrons is reduction.

OIL RIG – oxidation is loss, reduction is gain.

Cu + 2Ag+ = Cu2+ + 2Ag

…two electrons transfer from metallic copper to silver ions.

The direction of electron transfer reactions is dictated by the relative electron energy or redox potential of the reacting species.  In the above case, we go from Cu2+/Cu down to Ag+/Ag.

Zn + Cu2+ = Zn2+ + Cu

Zn + 2Ag+ = Zn2+ + 2Ag

No macroscopic change is seen.  Galvanic cell uses the electron flow.

dEo cell = Eo cathode – Eo anode

Standard Hydrogen Electrode

Reference half cell arbitrarily assigned to 0 volts.  The relevent reaction is:

SHE: 2H+ + e- = H2

Standard Half Cell Potentials

Potential        Half Cell Reaction

-3.05              Li+ + e- = Li

0                     2H+ +2e- = H2

+2.87               F2 + 2e- = 2F+

Half reactions with the most negative potentials are most likely to happen on the anode – proceed in the opposite direction.  Anode – oxidation.

Half reactions with the most positive potentials are most likely to happen on the cathode – proceed as written.  Cathode – reduction.

Review

anode oxidation, cathode reduction

PV = nRT

OIL RIG

k = products/reactants

IGL: point source, random motion, elastic collisions, high temperatures, low pressure

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