In galvanic cells, the cathode and anode are separated into two containers or half-cells. The cathode and anode are connected through a wire or other apparatus, and the two solutions are connected through a salt bridge. Electrons flow from the anode, through the wire, and into the cathode. Since the charge distribution is changing, the ions in the solutions redistribute via the salt bridge to equalize the charge. The salt bridge is composed of an inert salt that will not react with the ions passing through the bridge. The electrons are released at the anode through a half cell reaction. An individual half cell reaction represents the oxidation or reduction that occurs at a given electrode. An example of a half cell reaction that occurs at an anode is
The liberated electrons then travel to the cathode, where a reduction occurs:
Equations (1) and (2) in particular describe the half cell reactions of a Daniell cell, in which a zinc rod is placed in an aqueous solution of and a copper rod is
