Electrochemistry Chemical Change and Electrical Work

Oxidation-reduction (redox) reactions Involve the movement of electrons. The half-reaction method of balancing a redox reaction separates the overall reaction into two half-reactions. This reflects the actual separation of the two half-cells in an electrochemical cell 

In a voltaic cell, a spontaneous redox reaction (AG 0) is separated into an oxidation half-reaction (anode half-cell] and a reduction halfreaction (cathode half-celf). Electrons flow from anode to cathode through an external circuit, releasing electrical energy, and ions flow through a salt bridge to complete the circuit and balance the charge within the celi. 

The anode has a greater abiiity to give up eiectrons than the cathode, and the cell potential, or voltage (fceii), is related to this difference. A negative AG correiates with a positive Eceii- Under standard-state conditions, each haif-reaction is associated with a standard electrode potential (Ehaif -cell)- 

The standard free energy change (AG°), the standard ceii potentiai (Ey, and the equiiibrium constant (K) are interreiated. 

Ceil potential (Eceii) changes during operation of the cell. The Nemst equation shows that Eceii depends on Ecew and a term for the potential at nonstandard-state concentrations. During the operation of a typical voltaic cell, reactant concentration starts out higher than product concentration, gradually becomes equal to it, and then less than it, until Q = K and the cell can do no more work. 

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CHAPTER 21 Electrochemistry Chemical Change and Electrical Work... 

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