Voltaic cells agents

A voltaic cell that converts the chemical energy of a fuel and an oxidizing agent directly into electriacl energy on a continuous basis. 

In voltaic cells, it is possible to carry out the oxidation and reduction halfreactions in different places when suitable provision is made for transporting the electrons over a wire from one half-reaction to the other and to transport ions from each half-reaction to the other in order to preserve electrical neutrality. The chemical reaction produces an electric current in the process. Voltaic cells, also called galvanic cells, are introduced in Section 17.1. The tendency for oxidizing agents and reducing agents to react with each other is measured by their standard cell potentials, presented in Section 17.2. In Section 17.3, the Nernst equation is introduced to allow calculation of potentials of cells that are not in their standard states. 

Fig. 3-1. An example of a voltaic cell spontaneously generating current in a wire. The impetus for electron movement in the wire comes from the difference in oxidation potential between Zn,s) and Cu. The reducing agent, Zn(s), gives up electrons at the anode to become Zn ". The oxidising agent, Cu acquires electrons at the cathode and plates-out on the copper electrode as Cu(s). The semi-permeable membrane allows ions to move between the two solutions preventing charge imbalances and completing the electrical circuit (from Hamilton, 1998).

Figure 3-1 shows an example of a voltaic cell. A zinc electrode is immersed in a solution of NaCl and a copper electrode in a solution of CuCl2,with a semi-permeable membrane separating the two solutions. If a wire connects the two electrodes, electrons flow spontaneously from the zinc electrode to the copper electrode because is a stronger oxidising agent than Zn(s). At the copper cathode, Cu in the solution is reduced to CU(s) by electrons that are the product of the simultaneous oxidation of Zn(s) to Zn at the zinc anode. The difference in oxidation potential of the two metals results in a differential of approximately 1.10 volts between the two electrodes (assuming equal concentrations of Cu and Zn ). Across the membrane, Cf ions must move toward or... 

Compare various voltaic cells to determine the relative strengths of oxidizing and reducing agents... 

In Exercise 20.25 you chose from a list of half-reactions to construct voltaic cells of specified, relative emf values. The reaction shown in the Formation of Silver Crystals movie (eChapter 20.2) can be represented with two of the half-reactions listed in Exercise 20.25. (a) Write and balance the equation for the reaction in the movie, (b) Which species is the oxidizing agent and which is the reducing agent in this reaction ... 

The process continues until either all the zinc electrode or all the copper(ii) ions are consumed. The zinc is acting as a reducing agent and copper(ii) ions are acting as an oxidizing agent. By definition, the anode in a voltaic cell is the electrode at which oxidation occurs and the cathode is the electrode at which reduction occurs. 

Any two different half-cells can be combined together to form a voltaic cell and allow the electrons to flow from the reducing agent to the oxidizing agent. The resulting movement of electrons allows useful work to be done and also allows chemists to measure the tendency for a redox reaction to occur. 

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