Electrochemistry

Oxidation States

• Neutral compound oxidation state = 0

• Polyatomic ions oxidation state = overall ion charge

Oxidation v. electrons

• Loses e^-

• Acts as the reducing agent

Reduction v. electrons

• Gains e^-

• Acts as the oxidizing agent

Balancing redox reactions:

1. Split into oxidation / reduction half-reactions

2. Balance non-O and non-H elements

3. Balance O using H₂O

4. Balance H using H⁺

5. Balance charge using electrons e^-

What are galvanic (voltaic) cell?

Spontaneous chemical reactions that generate electrical energy.

What are electrolytic cells?

Non-spontaneous reactions driven by an external electrical power source.

What is an anode?

The site of oxidation

What is a cathode?

The site of reduction

Cell Notation

• Anode | Reactant | Product || Reactant | Product | Cathode

• Single bar (|) = Phase boundary

• Double bar (||) = Salt bridge

What is salt bridge?

Purpose of maintaining electrical neutrality by allowing the migration of spectator ions.

Cell potential

• E°_cell = E°_cathode - E°_anode

• + E°_cell

• - E°_cell

Gibbs Free Energy v. cell potential

ΔG° = -nFE°cell

The Nernst equation

E = E° - (0.0592/n)(logQ)

Negative E°_cell

• Nonspontaneous forward reaction

• ΔG > 0

Positive E°_cell

• Spontaneous forward reaction

• ΔG < 0

More reactants (Q < 1)

E_{cell >} E°_cell

More products (Q > 1)

E_{cell <} E°_cell