Electrochemistry
The study of chemical reactions that
produce electrical current or are
driven to occur by applying an
electrical current.
Chemical
potential
energy
galvanic cell
Electrical
potential
energy
electrolytic cell
Where is the chemical potential energy stored?
Reactions
• In aqueous solution or molten salts
(ionic reactions)
• Heterogeneous – at electrode
surfaces
– Gases formation
– Plating of metals/eroding (dissolving)
metals
Solutions
• Homogeneous mixtures – variable
composition
• Two components:
– Solute
– Solvent (usually water – aqueous
solutions)
• Molarity – unit of concentration
– M = moles of solute/VL of solution
– Moles = M x VL
Types of solutes
• Non-electrolytes – do not dissociate,
remain as molecules in solution (all
molecules) such as sugars, alcohols
sugar (s)  sugar (aq)
Types of solutes continued
• Electrolytes – dissociate in solution
– Strong electrolytes -100% dissociation
into ions – high conductivity (all ions)
NaCl (s)  Na+ (aq) + Cl- (aq)
– Weak electrolytes – partial dissociation
into ions – poor/low conductivity (ions and
molecules)
CH3COOH (aq) H+ (aq) + CH3COO- (aq)
Solubility
• “like dissolves like”
– Ionic salts - Water
– Molecular compounds – non-aqueous
solvents
• Usually solubility increases with
increasing temperature
• Solubility rules
Types of conduction movement of charged particles
• Metallic conduction - electrons in metals
• ionic or electrolytic conduction - ions in
molten salts or aqueous solutions
• gaseous conduction - ions and electrons
in the gas phase (atomic plasmas)
Geiger-Muller Tube for radioactive
decay particles
Redox Processes electron transfer
• oxidation -
– loss of electrons
– oxidation number increases
Ag  Ag+ + e-
• reduction -
– gain in electrons
– decrease in oxidation number
Fe+2 + 2e-  Fe
Redox Reactions
Both oxidation and reduction MUST
occur in the reaction and the number of
electrons exchanged MUST be balanced
Consider silver plating a copper penny
Cu + 2Ag+
 Cu+2 + 2 Ag
What is being oxidized?
Cu  Cu+2 + 2e-
What is being reduced?
Ag+ + e-  Ag
MUST balance number of electrons exchanged
x 2