As electrons leave the vessel in which oxidation is occurring, a net positive
charge accumulates in the vessel. A net negative charge grows in the reduction
vessel, where the electrons are ending up. If these charge buildups were not
neutralized, then the redox reaction would be short-lived, since electrons will not
readily flow from a region of positive charge to a region of negative charge. So,
what neutralizes any excess charge buildup? The salt bridge does. The salt
bridge contains a cation and an anion that don’t participate in the redox reaction.
As positive charge accumulates in the oxidation vessel, anions flow into it from
the salt bridge. Cations leave the salt bridge to flow into the reduction vessel and
neutralize the negative charge buildup. In our electrochemical cell, we would fill
the salt bridge with an aqueous solution of potassium chloride (KCl). K+ ions
flow into the reduction vessel, and Cl− ions flow into the oxidation vessel.
We can connect a voltmeter to the wire to measure the voltage (electric
potential) of the electrochemical cell. The actual electric potential is theoretically
equal to E^0 cell; however, electrical resistance in the wire always causes the actual
electric potential to be less than E^0 cell. As an electrochemical cell runs, its
voltage decreases. When the voltage becomes 0, the spontaneous redox reaction
has attained equilibrium, and the electrochemical cell is “dead.”
Electrolysis
Electrolysis is the process by which electrical energy is put into a
nonspontaneous redox reaction to force it to occur. This means that, during
electrolysis, electrical energy is converted into chemical energy. Electrolysis is a
useful way to separate ionic compounds into their constituent elements. For
example, running electricity through a sample of molten NaCl can produce
sodium metal (Na) and chlorine gas (Cl 2 ).
Electroplating is a type of electrolysis in which one metal is deposited on
another. For instance, a coating of silver can be electroplated onto a cheaper
metal to make quality silverware.
Electrochemical CellsGalvanic Cells—If the sum of the standard electrode potentials for the
oxidation half-reaction and the reduction half-reaction is greater than zero,