17.2 Galvanic Cells

• It is often convenient to separate oxidation-reduction reactions into half-reactions in order to balance the equation and emphasize the actual chemical transformations.

• When a clean piece of copper metal is placed in a solution of silver nitrate, silver metal begins to form and copper ion pass into the solution.
• The blue color of the solution shows the presence of copper.
• The reaction may be split into two parts.

• Each reaction can be considered individually, because half-reactions separate oxidation from the reduction.

• An oxidation reduction reaction occurs when a piece of copper is placed into a solution of silver nitrate.
• As the reaction proceeds, the solution becomes blue because of the copper ion present, and silver metal is deposited on the copper strip as the silver ion are removed from solution.
• There is a metal in this picture.
• The anode is connected to a wire and the other terminal is connected to a silver electrode.
• There is no current flow at this point because the circuit is open.
• The circuit is closed using a bridge.
• The salt bridge consists of a concentrated, nonreactive, electrolyte solution.
• When electrons flow from left to right through the wire, they pass through a porous plug on the left into the copper nitrate solution.
• The beaker on the left is neutral by the charge on the copper(II) ion that are produced in the solution.

• The added cations keep the beaker on the neutral side.

• Without the bridge, the compartments wouldn't stay neutral and the current wouldn't flow.
• There is no need for a salt bridge if the two compartments are in direct contact.
• The energy per unit charge available from the oxidation-reduction reaction is a measure of the cell potential.

• A is the current in amperes and C is the charge in coulombs.
• The energy in joules can be obtained if the charge in coulombs is multiplied by the volts.

• In a standard galvanic cell, the half-cells are separated and the electrons can flow through an external wire.

• There is a lot going on in this system so it is useful to summarize things.

• oxidation occurs in the left half-cell and the anode is in the left half-cell.

• The right half-cell has the cathode because reduction occurs here.

• The left half-cell isOxidation in the figure.

• The right half-cell is where the reduction occurs.

• The inherent differences in the nature of the materials used to make the two half-cells lead to the cell potential being +0.46 V.

• The salt bridge must be present to close the circuit and both an oxidation and reduction must occur for the current to flow.

• A shorthand notation is used to describe galvanic cells.
• It works for other types of cells as well.
• A double line and a phase boundary are marked by a vertical line.
• Information about the anode is written to the left, followed by the solution, then the bridge, and finally the solution to the right.
• The initial concentrations of the various ion are usually included.

• The Daniell cell is one of the least complicated cells.
• It is possible to make a battery by placing a copper electrode at the bottom of a jar and covering the metal with a copper sulfate solution.
• A zinc sulfate solution is floated on top of a copper sulfate solution and a zinc electrode is placed in the zinc sulfate solution.
• An electric current can flow if the copper and zinc are connected.
• An example of a cell without a salt bridge is this one.

• Some oxidation-reduction reactions involve species that are poor conductors of electricity, and so an electrode is used that does not participate in the reactions.
• There are many chemical reactions in which the gold, Platinum, and Graphite are not present.
• At the anode on the left, magnesium undergoes oxidation, while hydrogen ion reduction takes place on the right.

• Platinum and gold are generally unreactive.

• The oxidation and reduction half-reactions can be written using cell notation.

• When three electrons are lost to form Cu, Cu is reduced as it gains two electrons to form Cu.
• Oxidation occurs at the anode.

• When one electron is lost to form Fe3+, and five electrons are gained to form Mn2+, it undergoes oxidation.

• Oxidation occurs at the anode.

• The galvanic cell is where copper and zinc are reduced to copper and zinc, respectively.