Chapter 18: Introduction to Electrochemistry CHE 321: Quantitative Chemical Analysis Dr. Jerome Williams, Ph.D. Saint 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)

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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) + Cl 2 (g) → 2 Na + Cl – (s) Na is oxidized, Cl is reduced Na is the reducing agent, Cl 2 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

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Table 18-1 p464

Figure 18-9 p466

Figure p469

Nernst Equation