Chapter 18: Introduction to Chapter 18: Introduction to ElectrochemistryElectrochemistry
CHE 321: Quantitative Chemical AnalysisCHE 321: Quantitative Chemical AnalysisDr. Jerome Williams, Ph.D.Dr. Jerome Williams, Ph.D.
Saint Leo UniversitySaint Leo University
Overview
• Electrochemistry
• Electrochemical Cells– Oxidation & Reduction– Electrodes
• Oxidation & Reduction
• Current, Voltage, & Cell Potential
• Cell Notation
Electrochemistry• Electrochemistry is the study of oxidation-
reduction (redox) reactions that produce or require an electric current
• Conversion between chemical energy and electrical energy is carried out in an electrochemical cell
Electrochemical Cells• Two types of Electrochemical cells
• Voltaic (Galvanic) cells -spontaneous redox reactions take place
• Electrolytic cells are where non-spontaneous redox reactions can be made to occur by the addition of electrical energy (process is termed electrolysis)
Oxidation & Reduction• Oxidation is the process that occurs when
– oxidation number of an element increases– element loses electrons– compound adds oxygen– compound loses hydrogen– half-reaction has electrons as products
• Reduction is the process that occurs when– oxidation number of an element decreases– element gains electrons– compound loses oxygen– compound gains hydrogen– half-reactions have electrons as reactants
Oxidation–Reduction• oxidation and reduction must occur simultaneously
– if an atom loses electrons another atom must take them
• the reactant that reduces an element in another reactant is called the reducing agent– the reducing agent contains the element that is oxidized
• the reactant that oxidizes an element in another reactant is called the oxidizing agent– the oxidizing agent contains the element that is reduced
2 Na(s) + Cl2(g) → 2 Na+Cl–(s)Na is oxidized, Cl is reduced
Na is the reducing agent, Cl2 is the oxidizing agent
Electrodes• Anode
– electrode where oxidation occurs– anions attracted to it– connected to positive end of battery in
electrolytic cell– loses weight in electrolytic cell
• Cathode– electrode where reduction occurs– cations attracted to it– connected to negative end of battery in
electrolytic cell– gains weight in electrolytic cell
• electrode where plating takes place in electroplating