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Cover Electrode Potentials

Richard G Compton and Giles H W Sanders

Electrode Potentials provides an introduction to the science of equilibrium electrochemistry, specifically addressing the topics of electrode potentials and their applications. It builds on a knowledge of elementary thermodynamics by giving the reader an appreciation of the origin of electrode potentials, and shows how these are used to deduce a wealth of chemically important information and data such as equilibrium constants; the free energy, enthalpy and entropy changes of chemical reactions; activity coefficients; and the selective sensing of ions. The emphasis throughout is on understanding the foundations of the subject and how it may be used to study problems of chemical interest.


Cover Electrode Potentials

Worked examples and problems  

This chapter includes examples of problems based on standard electrode potentials, such as calculating the equilibrium constants for reactions at 25°C in aqueous solutions. It examines the strategy associated with a formal cell reaction with the cell, which includes the potential determining equilibrium at the right-hand electrode. It also explores a reaction that is thermodynamically downhill, which is the process that would occur if the cell was short circuited. The chapter talks about the spontaneous cell reaction which occurs when the cell is short circuited, and which depends on cell concentrations. It analyses the reaction that involves the pure solid metal chlorides and pure elements in their standard states, in which free energies evaluated are standard free energies regardless of the concentration of hydrochloric acid in the cell.


Cover Electroanalysis

Potentiometric sensors  

This chapter describes the functioning of potentiometric sensors, how they can be usefully employed, and in which experimental situations. Potentiometric sensors work through the measurement of an equilibrium potential, i.e. the potential at zero current, of the sensor versus a suitable reference electrode. These potentials are a function of the activity of the species in solution, not of their concentration. The Debye–Hückel equation relates concentrations to activities and can often be employed; indeed, potentiometric measurements can be used to test the Debye–Hückel theory. For potentiometric sensors to be useful, they must have a sufficiently fast response and be sufficiently selective in media containing various species, besides having a sufficiently good detection limit. The chapter then considers the functioning of ion-selective electrodes; the types of selective electrodes; miniaturisation strategies; and the criteria for choosing a potentiometric sensor.


Cover Molecular Spectroscopy

Vibrational spectroscopy  

This chapter defines vibrational motion, which is a periodic, concerted displacement of the nuclei in a molecule that leaves the centre of mass unaltered in laboratory space. It explains that the appropriate linear combination of the displacements of a nucleus from its equilibrium position is called the vibrational coordinate, which is used to describe a particular vibrational motion. It also mentions the polyatomic molecule. This has several distinct vibrational modes, while the diatomic molecule only has one. The chapter reviews two distinct contributions to energy: the kinetic part that arises from the motion of the nuclei and the potential part that comes from the compression or expansion of the bond from its equilibrium value. It highlights the form of the potential energy curve. This shows that molecular energy increases rapidly as the charged particles in the molecule experience strong repulsive forces.