What is Electrochemistry?
Electrochemistry is the study of electrical charges moving between electrodes (usually a metal) and aqueous ionic solutions (electrolytes - containing the cations of the metals used in the electrodes). Certain chemical reactions, namely oxidation-reduction reactions, are responsible for spontaneously exchanging electrons between species. When this exchange is setup in an electrochemical cell, ions move in specific directions, allowing for a voltage (electrical potential) to be measured.
Voltaic or Galvanic Cells
Pictured above is the Daniel cell, a common voltaic cell that utilizes an exchange of electrons between copper and zinc. In a voltaic cell, the redox reaction proceeds spontaneously, with electrons lost from the more reactive metal, causing it to be oxidized. Electrons are then transferred to the less active metal, causing it to be reduced.
The Nernst equation gives the overall voltage (or electromotive force, emf) by summing the individual half-cell potentials of the oxidation and reduction process. The concentration of the electrolytes, as well as temperature and reaction quotient (Q) must be factored into the calculation. When performing problems, it is usually assumed that the temperature is 298.15 K and that the electrolytes have a concentration of 1 M.