Chapter 14: Electrochemistry & Thermodynamics

Electrochemistry & Thermodynamics on Electrochemistry introduces the core concepts of chemical reactions involving changes in oxidation state (valence state), driven by the transfer of electrons. The resultant thermodynamic driving force is measured as an electric voltage, known as the electromotive force (EMF), which can be measured when the reaction is conducted in a galvanic cell—a system designed to convert chemical energy into electrical work. The crucial quantitative link between the Gibbs free energy change (change in G) for the cell reaction and the EMF is established by the Nernst equation (though the equation itself is not written here) and depends on the charge transferred and Faraday’s constant (96,487 coulombs per mole). The text explains how charge separation and potential differences develop at the interface between a metal and an electrolyte. Specific examples of cells include the classic Daniell cell (zinc and copper electrodes) and various concentration cells, where electrodes are identical but solutions differ in composition. A critical practical example is the oxygen concentration cell, which utilizes lime-stabilized zirconia as a solid electrolyte, functioning only via the transport of oxygen ions, allowing for the measurement of oxygen pressures or activities. Further thermodynamic properties, such as the molar entropy change (change in S) and the molar enthalpy change (change in H) associated with the cell reaction, can be derived directly from the temperature coefficient of the EMF. For solutions, the chapter defines composition scales like molality and molarity and introduces concepts necessary for describing non-ideal aqueous solutions, such as the mean ionic molality and the mean ion activity coefficient. To quantify potentials, the Standard Hydrogen Electrode (SHE) is arbitrarily assigned a zero potential, enabling the compilation of the electrochemical series, which lists standard reduction potentials useful for predicting reaction spontaneity and calculating the solubility product (Ksp). Practical applications are detailed in the section on batteries (including non-rechargeable primary cells and rechargeable secondary cells), specifically discussing the Lead-Acid, Nickel-Cadmium, and modern Lithium-ion batteries, noting the important process of Lithium ion intercalation into solid electrodes during charging and discharging. The chapter concludes with Pourbaix diagrams (potential-pH diagrams), which graphically map the thermodynamic stability domains of solids and ions in aqueous solutions, demonstrated through the complex equilibria of aluminum and used to define the boundaries of water’s thermodynamic stability.