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)

p443

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

Figure 18-2a p447

Figure 18-2b p447

Figure 18-2c p447

Figure 18-4a p453

Figure 18-4b p453

Figure 18-4c p453

Figure 18-5 p455

Figure 18-6 p457

Figure 18-7 p458

Figure 18-8 p459

Table 18-1 p464

Figure 18-9 p466

Figure 18-10 p469

Nernst Equation