As demonstration of spontaneous chemical change, the image shows the result of
immersing a coiled wire of copper into an aqueous solution of silver nitrate. A gradual
but visually impressive change spontaneously occurs as the initially colorless solution
becomes increasingly blue, and the initially smooth copper wire becomes covered with
a porous gray solid.
A copper wire and an aqueous solution of silver nitrate (left) are brought into contact
(center) and a spontaneous transfer of electrons occurs, creating blue Cu (aq) and gray
2+
Ag(s) (right).
These observations are consistent with (i) the oxidation of elemental copper to yield
copper(II) ions, Cu2+(aq), which impart a blue color to the solution, and (ii) the reduction
of silver(I) ions to yield elemental silver, which deposits as a fluffy solid on the copper
wire surface. And so, the direct transfer of electrons from the copper wire to the
aqueous silver ions is spontaneous under the employed conditions. A summary of this
redox system is provided by these equations:
overall reaction:oxidation half-reaction:reduction half-
reaction:Cu(s)+2Ag+(aq)⟶Cu2+(aq)+2Ag(s)Cu(s)⟶Cu2+(aq)
+2e−2Ag+(aq)+2e−⟶2Ag(s)overall reaction:Cu(s)+2Ag+(aq)⟶Cu2+(aq)
+2Ag(s)oxidation half-reaction:Cu(s)⟶Cu2+(aq)+2e−reduction half-reaction:2Ag+(aq)
+2e−⟶2Ag(s)
Consider the construction of a device that contains all the reactants and products of a
redox system like the one here, but prevents physical contact between the reactants.
Direct transfer of electrons is, therefore, prevented; transfer, instead, takes place
indirectly through an external circuit that contacts the separated reactants. Devices of
this sort are generally referred to as electrochemical cells, and those in which a
spontaneous redox reaction takes place are called galvanic cells (or voltaic cells).
A galvanic cell based on the spontaneous reaction between copper and silver(I) is
depicted in the above image. The cell is comprised of two half-cells, each containing
the redox conjugate pair (“couple”) of a single reactant. The half-cell shown at the left
contains the Cu(0)/Cu(II) couple in the form of a solid copper foil and an aqueous
solution of copper nitrate. The right half-cell contains the Ag(I)/Ag(0) couple as solid
silver foil and an aqueous silver nitrate solution. An external circuit is connected to each
half-cell at its solid foil, meaning the Cu and Ag foil each function as an electrode . By
definition, the anode of an electrochemical cell is the electrode at which oxidation
immersing a coiled wire of copper into an aqueous solution of silver nitrate. A gradual
but visually impressive change spontaneously occurs as the initially colorless solution
becomes increasingly blue, and the initially smooth copper wire becomes covered with
a porous gray solid.
A copper wire and an aqueous solution of silver nitrate (left) are brought into contact
(center) and a spontaneous transfer of electrons occurs, creating blue Cu (aq) and gray
2+
Ag(s) (right).
These observations are consistent with (i) the oxidation of elemental copper to yield
copper(II) ions, Cu2+(aq), which impart a blue color to the solution, and (ii) the reduction
of silver(I) ions to yield elemental silver, which deposits as a fluffy solid on the copper
wire surface. And so, the direct transfer of electrons from the copper wire to the
aqueous silver ions is spontaneous under the employed conditions. A summary of this
redox system is provided by these equations:
overall reaction:oxidation half-reaction:reduction half-
reaction:Cu(s)+2Ag+(aq)⟶Cu2+(aq)+2Ag(s)Cu(s)⟶Cu2+(aq)
+2e−2Ag+(aq)+2e−⟶2Ag(s)overall reaction:Cu(s)+2Ag+(aq)⟶Cu2+(aq)
+2Ag(s)oxidation half-reaction:Cu(s)⟶Cu2+(aq)+2e−reduction half-reaction:2Ag+(aq)
+2e−⟶2Ag(s)
Consider the construction of a device that contains all the reactants and products of a
redox system like the one here, but prevents physical contact between the reactants.
Direct transfer of electrons is, therefore, prevented; transfer, instead, takes place
indirectly through an external circuit that contacts the separated reactants. Devices of
this sort are generally referred to as electrochemical cells, and those in which a
spontaneous redox reaction takes place are called galvanic cells (or voltaic cells).
A galvanic cell based on the spontaneous reaction between copper and silver(I) is
depicted in the above image. The cell is comprised of two half-cells, each containing
the redox conjugate pair (“couple”) of a single reactant. The half-cell shown at the left
contains the Cu(0)/Cu(II) couple in the form of a solid copper foil and an aqueous
solution of copper nitrate. The right half-cell contains the Ag(I)/Ag(0) couple as solid
silver foil and an aqueous silver nitrate solution. An external circuit is connected to each
half-cell at its solid foil, meaning the Cu and Ag foil each function as an electrode . By
definition, the anode of an electrochemical cell is the electrode at which oxidation
