Galvanic cells are electrochemical devices used to generate energy from chemical reactions. The reactions of galvanic cells are spontaneous, and by harnessing the energy of oxidation and reduction half-reactions, the cell supplies electrical energy to do work.
The voltage (E) of a given galvanic cell varies with changes to the concentrations of reactants and products in the redox reaction. This can be calculated using the Nernst equation:
In the Nernst equation, E° represents the standard cell voltage, n is the number of moles of electrons exchanged in the balanced equation, and Q is the reaction quotient. As the reaction proceeds, the voltage of a galvanic cell will change. One specific type of galvanic cell is the Daniell cell, which harnesses half-reactions with zinc and copper to generate useful electrical work:
Cu2+(aq) + 2e– → Cu(s) (E° = +0.34 V)
Before attempting to construct a Daniell cell, a student places a solid strip of zinc in a copper sulfate solution. The student observes that the zinc strip dissolves and solid copper replaces it. The student prepares two beakers, one filled with a 1 M copper sulfate solution and another with 1 M zinc sulfate solution. The student then connects the two beakers using a salt bridge. Finally, the student places a copper strip in the copper sulfate solution and a zinc strip in the zinc sulfate solution. The two metal strips are connected via a metal wire. After a few moments, the student uses a voltmeter to measure the reaction progress, and finds that a potential difference exists between the electrodes of the Daniell cell.
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