Oxidation: Zn(s) → Zn2+(aq) + 2e−; E^0 ox = 0.76 V
Reduction: Cu2+(aq) + 2e− → Cu(s); E^0 red = 0.34 VFor the above reaction, E^0 cell is 0.76 V + 0.34 V = 1.10 V. Since E^0 cell > 0, this
redox reaction is spontaneous, which means that we can turn the energy that this
reaction releases into electrical energy. But how?
If we simply drop some zinc metal into an aqueous solution of Cu2+ ion (say, a
water solution of Cu(NO 3 ) 2 , this spontaneous redox reaction will happen.
Electrons will leave the zinc metal as it is oxidized and be captured by the Cu2+
ions, which will be reduced. All of this will happen, yet we will get no electrical
energy out of the reaction. Why not? Because the electrons will immediately
travel from the zinc atoms to the Cu2+ ions. Electrical energy involves the flow
of electrons, so if we want to derive electrical energy from this reaction, we must
force the electrons that leave zinc to flow through a wire in order to reach Cu2+.
This is precisely what the electrochemical cell does. In an electrochemical cell,
the oxidation and reduction half-reactions occur in separate vessels. Each vessel
contains an aqueous solution containing the ions participating (as reactants or
products) in the reaction. For example, we can use Zn(NO 3 ) 2 (aq) and
Cu(NO 3 ) 2 (aq) for the redox reaction shown on the previous page. A strip of
metal called an electrode is placed in each solution; each electrode is made out
of a metal that also participates in the reaction. The electrode in the vessel in
which oxidation occurs is called the anode. The cathode is the electrode in the
vessel in which reduction takes place. Each electrode is made out of a metal that
also participates in the reaction. In our electrochemical cell, the anode is a strip
of zinc metal, and the cathode is a strip of copper metal.
AN OX and RED CATOxidation occurs at the anode.Reduction occurs at the cathode.