Redox Reactions and Electrochemical Cells

1 Electrochemical Cells and Redox Reactions Example of Daniell s Galvanic Cell 

An electrochemical cell is a device that consists of two electronic conductors (usually a metal) called electrodes each dipping into separate ionic solutions. They are inserted within an electrical circuit (see Chap. 2 and Figs. 2.1 and 2.2). Hence, a cell consists of two compartments, each of which consists of an electrode and a solution into which it dips. Both electrodes seldom dip into the same electrolytic solution. In the literature, the word electrode may refer to the whole compartment where it stands. In brief, an electrochemical cell is a system in which one of the electronic conductors acts as an electron source for particules in an ionic conductor (the solution) and the other as an electron sink that receives electrons from the ionic conductor. 

From an operational standpoint, electrochemical cells in which faradaic currents are flowing are classified as either galvanic or electrolytic cells (a faradaic current occurs if charges, e.g., electrons, are transferred across the metal-solution interface— see electrochemistry). The example of Daniell s cell permits us to clarify these points. 

Electrochemistry, certainly one of the most important areas of applied thermodynamics, is the study of the relationship between chemical change and electrical work. It is typically investigated through the use of electrochemical cells, systems that incorporate a redox reaction to produce or utilize electrical energy. 

Whether an electrochemical process releases or absorbs free energy, it always involves the movement of electrons from one chemical species to another in an oxidation-reduction (redox) reaction. In this section, we review the redox process and describe the half-reaction method of balancing redox reactions. Then we see how such reactions are used in electrochemical cells. 

Hydrogen ion gains electrons. H ogen Ion Is the oxidizing agent and becomes reduced. The mddation number of H decreases from 4l to 0. 

Half-Reaction Method for Balancing Redox Reactions 

The half-reaction method for balancing redox reactions divides the overall redox reaction into oxidation and reduction half-reactions. Each half-reaction is balanced for atoms and charge. Then, one or both are multiplied by some integer to make electrons gained equal electrons lost, and the half-reactions are recombined to give the balanced redox equation. The half-reaction method is commonly used for studying electrochemistry because 

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Important for understanding oxidation-reduction redox) reactions and electrochemical cells... 

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