4.6 CHAPTER 4. ELECTROCHEMICAL REACTIONS
At the anode:
2 O^2 − → O 2 (g) + 4e−
The overall reaction is as follows:
2 Al 2 O 3 → 4 Al + 3O 2
The only problem with this process is that the reaction is endothermic and large amounts
of electricity are neededto drive the reaction. The process is therefore very expensive.
Chapter 4 — Summary
See the summary presentation ( Presentation: VPmyw atwww.everythingscience.co.za)
- An electrochemical reaction is one where either a chemical reaction produces
an external voltage, or where an external voltagecauses a chemical reaction to
take place.
- In a galvanic cell a chemical reaction produces a current in the external circuit.
An example is the zinc-copper cell.
- A galvanic cell has a number of components. It consists of two electrodes, each
of which is placed in aseparate beaker in an electrolyte solution. The two elec-
trolytes are connected by a salt bridge. The electrodes are connected two each
other by an external circuit wire.
- One of the electrodes is the anode, where oxidation takes place. The cathode is
the electrode where reduction takes place.
- In a galvanic cell, thebuild up of electrons at the anode sets up a potential
difference between thetwo electrodes, and thiscauses a current to flow in the
external circuit.
- A galvanic cell is therefore an electrochemical cell that uses a chemical reaction
between two dissimilar electrodes dipped in an electrolyte to generate anelectric
current.
- The standard notation for a galvanic cell such asthe zinc-copper cell is asfollows:
Zn|Zn2+||Cu2+|Cu
where
| = a phase boundary (solid/aqueous)
|| = the salt bridge
- The galvanic cell is used in batteries and in electroplating.
- An electrolytic cell is an electrochemical cell that uses electricity todrive a non-
spontaneous reaction. In an electrolytic cell, electrolysis occurs, which is a pro-
cess of separating elements and compounds using an electric current.
