Electrochemistry: The branch of chemistry that covers the relative strengths of oxidants and reductants, the production of electric current from chemical reactions, and the use of electricity to produce chemical change.
Electrode: A conductor of electricity, commonly a metal or graphite in contact with an electrolyte in an electrochemical cell.
Half-cell: An electrode and the couple it is in contact with
The electrode may be one of the species of the couple or an inert species as with zinc and platinum respectively above. The vertical line represents a phase boundary.
Galvanic cell: an electrochemical cell that produces electricity from a chemical reaction.
Cell potential or electromotive force: symbol E, the electric potential difference between the electrodes of a galvanic cell when no current is flowing. In the above representation of a galvanic cell it is the electrode potential of the right hand electrode minus the electrode potential of the left hand electrode. It is normal to show the negative electrode on the left and the positive electrode on the right and thus express the cell potential as a positive quantity.
Standard hydrogen electrode: symbol she, a reference electrode defined as having zero electrode potential. It consists of a platinum electrode in contact with gaseous dihydrogen and aqueous hydronium ions under defined conditions.
Electrode potential (of a couple): symbol E(oxidised form/reduced form), also called reduction potential or redox potential is the electrode potential of that couple relative to the standard hydrogen electrode. More precisely it is the cell potential of a galvanic cell in which one half-cell is the standard hydrogen electrode, and is negative if the electrode of the couple is the negative electrode of that cell and positive if the electrode is the positive electrode of that cell.
The magnitude of a redox potential is a measure of the relative strength of an oxidant or reductant. The more positive the redox potential the stronger the oxidant (i.e. the greater its potential to oxidise some other species) and the weaker the reductant. Conversely the more negative the redox potential the stronger the reductant and the weaker the oxidant.
Table of electrode potentials: a table which lists the electrode potential of redox couples
Strong oxidant of a redox couple: An oxidant with a large positive redox potential
Strong reductant of a redox couple: A reductant with a large negative redox potential
As electrons flow spontaneously from the negative to the positive electrode the electode potentials can be used to deduce the direction of a redox reaction.
Electrons can flow from Zn to Cu2+ but not from Cu to Zn2+ Thus zinc metal can reduce copper ions to copper metal but copper metal cannot reduce zinc ions to zinc metal.
4. Sn can reduce Br2
5. O2 can oxidise Cl¯
6. Ag can reduce Cu2+
7. Fe3+ can oxidise I¯
For the cell
The cell potential is the difference of the two electrode potentials, i.e. the potential of the positive electrode minus the potential of the negative electrode.
Write the half reaction equations, the chemical equation for the overall cell reaction
8. Zn2+/Zn and Fe3+/Fe2+
Answer 9 10. Ag+/Ag and Cl2/Cl¯